--- a/src/HOL/Library/Float.thy Thu Jul 09 00:39:49 2015 +0200
+++ b/src/HOL/Library/Float.thy Thu Jul 09 00:40:57 2015 +0200
@@ -22,6 +22,7 @@
real_of_float_def[code_unfold]: "real \<equiv> real_of_float"
instance ..
+
end
lemma type_definition_float': "type_definition real float_of float"
@@ -34,7 +35,8 @@
declare [[coercion "real :: float \<Rightarrow> real"]]
lemma real_of_float_eq:
- fixes f1 f2 :: float shows "f1 = f2 \<longleftrightarrow> real f1 = real f2"
+ fixes f1 f2 :: float
+ shows "f1 = f2 \<longleftrightarrow> real f1 = real f2"
unfolding real_of_float_def real_of_float_inject ..
lemma float_of_real[simp]: "float_of (real x) = x"
@@ -43,40 +45,63 @@
lemma real_float[simp]: "x \<in> float \<Longrightarrow> real (float_of x) = x"
unfolding real_of_float_def by (rule float_of_inverse)
+
subsection \<open>Real operations preserving the representation as floating point number\<close>
lemma floatI: fixes m e :: int shows "m * 2 powr e = x \<Longrightarrow> x \<in> float"
by (auto simp: float_def)
-lemma zero_float[simp]: "0 \<in> float" by (auto simp: float_def)
-lemma one_float[simp]: "1 \<in> float" by (intro floatI[of 1 0]) simp
-lemma numeral_float[simp]: "numeral i \<in> float" by (intro floatI[of "numeral i" 0]) simp
-lemma neg_numeral_float[simp]: "- numeral i \<in> float" by (intro floatI[of "- numeral i" 0]) simp
-lemma real_of_int_float[simp]: "real (x :: int) \<in> float" by (intro floatI[of x 0]) simp
-lemma real_of_nat_float[simp]: "real (x :: nat) \<in> float" by (intro floatI[of x 0]) simp
-lemma two_powr_int_float[simp]: "2 powr (real (i::int)) \<in> float" by (intro floatI[of 1 i]) simp
-lemma two_powr_nat_float[simp]: "2 powr (real (i::nat)) \<in> float" by (intro floatI[of 1 i]) simp
-lemma two_powr_minus_int_float[simp]: "2 powr - (real (i::int)) \<in> float" by (intro floatI[of 1 "-i"]) simp
-lemma two_powr_minus_nat_float[simp]: "2 powr - (real (i::nat)) \<in> float" by (intro floatI[of 1 "-i"]) simp
-lemma two_powr_numeral_float[simp]: "2 powr numeral i \<in> float" by (intro floatI[of 1 "numeral i"]) simp
-lemma two_powr_neg_numeral_float[simp]: "2 powr - numeral i \<in> float" by (intro floatI[of 1 "- numeral i"]) simp
-lemma two_pow_float[simp]: "2 ^ n \<in> float" by (intro floatI[of 1 "n"]) (simp add: powr_realpow)
-lemma real_of_float_float[simp]: "real (f::float) \<in> float" by (cases f) simp
+lemma zero_float[simp]: "0 \<in> float"
+ by (auto simp: float_def)
+lemma one_float[simp]: "1 \<in> float"
+ by (intro floatI[of 1 0]) simp
+lemma numeral_float[simp]: "numeral i \<in> float"
+ by (intro floatI[of "numeral i" 0]) simp
+lemma neg_numeral_float[simp]: "- numeral i \<in> float"
+ by (intro floatI[of "- numeral i" 0]) simp
+lemma real_of_int_float[simp]: "real (x :: int) \<in> float"
+ by (intro floatI[of x 0]) simp
+lemma real_of_nat_float[simp]: "real (x :: nat) \<in> float"
+ by (intro floatI[of x 0]) simp
+lemma two_powr_int_float[simp]: "2 powr (real (i::int)) \<in> float"
+ by (intro floatI[of 1 i]) simp
+lemma two_powr_nat_float[simp]: "2 powr (real (i::nat)) \<in> float"
+ by (intro floatI[of 1 i]) simp
+lemma two_powr_minus_int_float[simp]: "2 powr - (real (i::int)) \<in> float"
+ by (intro floatI[of 1 "-i"]) simp
+lemma two_powr_minus_nat_float[simp]: "2 powr - (real (i::nat)) \<in> float"
+ by (intro floatI[of 1 "-i"]) simp
+lemma two_powr_numeral_float[simp]: "2 powr numeral i \<in> float"
+ by (intro floatI[of 1 "numeral i"]) simp
+lemma two_powr_neg_numeral_float[simp]: "2 powr - numeral i \<in> float"
+ by (intro floatI[of 1 "- numeral i"]) simp
+lemma two_pow_float[simp]: "2 ^ n \<in> float"
+ by (intro floatI[of 1 "n"]) (simp add: powr_realpow)
+lemma real_of_float_float[simp]: "real (f::float) \<in> float"
+ by (cases f) simp
lemma plus_float[simp]: "r \<in> float \<Longrightarrow> p \<in> float \<Longrightarrow> r + p \<in> float"
unfolding float_def
proof (safe, simp)
- fix e1 m1 e2 m2 :: int
- { fix e1 m1 e2 m2 :: int assume "e1 \<le> e2"
- then have "m1 * 2 powr e1 + m2 * 2 powr e2 = (m1 + m2 * 2 ^ nat (e2 - e1)) * 2 powr e1"
+ have *: "\<exists>(m::int) (e::int). m1 * 2 powr e1 + m2 * 2 powr e2 = m * 2 powr e"
+ if "e1 \<le> e2" for e1 m1 e2 m2 :: int
+ proof -
+ from that have "m1 * 2 powr e1 + m2 * 2 powr e2 = (m1 + m2 * 2 ^ nat (e2 - e1)) * 2 powr e1"
by (simp add: powr_realpow[symmetric] powr_divide2[symmetric] field_simps)
- then have "\<exists>(m::int) (e::int). m1 * 2 powr e1 + m2 * 2 powr e2 = m * 2 powr e"
- by blast }
- note * = this
- show "\<exists>(m::int) (e::int). m1 * 2 powr e1 + m2 * 2 powr e2 = m * 2 powr e"
- proof (cases e1 e2 rule: linorder_le_cases)
- assume "e2 \<le> e1" from *[OF this, of m2 m1] show ?thesis by (simp add: ac_simps)
- qed (rule *)
+ then show ?thesis
+ by blast
+ qed
+ fix e1 m1 e2 m2 :: int
+ consider "e2 \<le> e1" | "e1 \<le> e2" by (rule linorder_le_cases)
+ then show "\<exists>(m::int) (e::int). m1 * 2 powr e1 + m2 * 2 powr e2 = m * 2 powr e"
+ proof cases
+ case 1
+ from *[OF this, of m2 m1] show ?thesis
+ by (simp add: ac_simps)
+ next
+ case 2
+ then show ?thesis by (rule *)
+ qed
qed
lemma uminus_float[simp]: "x \<in> float \<Longrightarrow> -x \<in> float"
@@ -125,7 +150,8 @@
done
lemma div_numeral_Bit0_float[simp]:
- assumes x: "x / numeral n \<in> float" shows "x / (numeral (Num.Bit0 n)) \<in> float"
+ assumes x: "x / numeral n \<in> float"
+ shows "x / (numeral (Num.Bit0 n)) \<in> float"
proof -
have "(x / numeral n) / 2^1 \<in> float"
by (intro x div_power_2_float)
@@ -135,32 +161,38 @@
qed
lemma div_neg_numeral_Bit0_float[simp]:
- assumes x: "x / numeral n \<in> float" shows "x / (- numeral (Num.Bit0 n)) \<in> float"
+ assumes x: "x / numeral n \<in> float"
+ shows "x / (- numeral (Num.Bit0 n)) \<in> float"
proof -
- have "- (x / numeral (Num.Bit0 n)) \<in> float" using x by simp
+ have "- (x / numeral (Num.Bit0 n)) \<in> float"
+ using x by simp
also have "- (x / numeral (Num.Bit0 n)) = x / - numeral (Num.Bit0 n)"
by simp
finally show ?thesis .
qed
-lemma power_float[simp]: assumes "a \<in> float" shows "a ^ b \<in> float"
+lemma power_float[simp]:
+ assumes "a \<in> float"
+ shows "a ^ b \<in> float"
proof -
- from assms obtain m e::int where "a = m * 2 powr e"
+ from assms obtain m e :: int where "a = m * 2 powr e"
by (auto simp: float_def)
- thus ?thesis
+ then show ?thesis
by (auto intro!: floatI[where m="m^b" and e = "e*b"]
simp: power_mult_distrib powr_realpow[symmetric] powr_powr)
qed
-lift_definition Float :: "int \<Rightarrow> int \<Rightarrow> float" is "\<lambda>(m::int) (e::int). m * 2 powr e" by simp
+lift_definition Float :: "int \<Rightarrow> int \<Rightarrow> float" is "\<lambda>(m::int) (e::int). m * 2 powr e"
+ by simp
declare Float.rep_eq[simp]
lemma compute_real_of_float[code]:
"real_of_float (Float m e) = (if e \<ge> 0 then m * 2 ^ nat e else m / 2 ^ (nat (-e)))"
-by (simp add: real_of_float_def[symmetric] powr_int)
+ by (simp add: real_of_float_def[symmetric] powr_int)
code_datatype Float
+
subsection \<open>Arithmetic operations on floating point numbers\<close>
instantiation float :: "{ring_1, linorder, linordered_ring, linordered_idom, numeral, equal}"
@@ -192,16 +224,20 @@
declare less_float.rep_eq[simp]
instance
- proof qed (transfer, fastforce simp add: field_simps intro: mult_left_mono mult_right_mono)+
+ by (standard; transfer; fastforce simp add: field_simps intro: mult_left_mono mult_right_mono)+
+
end
lemma Float_0_eq_0[simp]: "Float 0 e = 0"
by transfer simp
-lemma real_of_float_power[simp]: fixes f::float shows "real (f^n) = real f^n"
+lemma real_of_float_power[simp]:
+ fixes f :: float
+ shows "real (f^n) = real f^n"
by (induct n) simp_all
-lemma fixes x y::float
+lemma
+ fixes x y :: float
shows real_of_float_min: "real (min x y) = min (real x) (real y)"
and real_of_float_max: "real (max x y) = max (real x) (real y)"
by (simp_all add: min_def max_def)
@@ -219,9 +255,9 @@
apply transfer
apply simp
done
- assume "a < b"
- then show "\<exists>c. a < c \<and> c < b"
- apply (intro exI[of _ "(a + b) * Float 1 (- 1)"])
+ show "\<exists>c. a < c \<and> c < b" if "a < b"
+ apply (rule exI[of _ "(a + b) * Float 1 (- 1)"])
+ using that
apply transfer
apply (simp add: powr_minus)
done
@@ -230,11 +266,11 @@
instantiation float :: lattice_ab_group_add
begin
-definition inf_float::"float\<Rightarrow>float\<Rightarrow>float"
-where "inf_float a b = min a b"
+definition inf_float :: "float \<Rightarrow> float \<Rightarrow> float"
+ where "inf_float a b = min a b"
-definition sup_float::"float\<Rightarrow>float\<Rightarrow>float"
-where "sup_float a b = max a b"
+definition sup_float :: "float \<Rightarrow> float \<Rightarrow> float"
+ where "sup_float a b = max a b"
instance
by (standard; transfer; simp add: inf_float_def sup_float_def real_of_float_min real_of_float_max)
@@ -250,20 +286,21 @@
lemma transfer_numeral [transfer_rule]:
"rel_fun (op =) pcr_float (numeral :: _ \<Rightarrow> real) (numeral :: _ \<Rightarrow> float)"
- unfolding rel_fun_def float.pcr_cr_eq cr_float_def by simp
+ by (simp add: rel_fun_def float.pcr_cr_eq cr_float_def)
lemma float_neg_numeral[simp]: "real (- numeral x :: float) = - numeral x"
by simp
lemma transfer_neg_numeral [transfer_rule]:
"rel_fun (op =) pcr_float (- numeral :: _ \<Rightarrow> real) (- numeral :: _ \<Rightarrow> float)"
- unfolding rel_fun_def float.pcr_cr_eq cr_float_def by simp
+ by (simp add: rel_fun_def float.pcr_cr_eq cr_float_def)
lemma
shows float_of_numeral[simp]: "numeral k = float_of (numeral k)"
and float_of_neg_numeral[simp]: "- numeral k = float_of (- numeral k)"
unfolding real_of_float_eq by simp_all
+
subsection \<open>Quickcheck\<close>
instantiation float :: exhaustive
@@ -311,39 +348,51 @@
assumes H: "\<And>n. (\<And>i. \<bar>i\<bar> < \<bar>n\<bar> \<Longrightarrow> P i) \<Longrightarrow> P n"
shows "P j"
proof (induct "nat \<bar>j\<bar>" arbitrary: j rule: less_induct)
- case less show ?case by (rule H[OF less]) simp
+ case less
+ show ?case by (rule H[OF less]) simp
qed
lemma int_cancel_factors:
- fixes n :: int assumes "1 < r" shows "n = 0 \<or> (\<exists>k i. n = k * r ^ i \<and> \<not> r dvd k)"
+ fixes n :: int
+ assumes "1 < r"
+ shows "n = 0 \<or> (\<exists>k i. n = k * r ^ i \<and> \<not> r dvd k)"
proof (induct n rule: int_induct_abs)
case (less n)
- { fix m assume n: "n \<noteq> 0" "n = m * r"
- then have "\<bar>m \<bar> < \<bar>n\<bar>"
+ have "\<exists>k i. n = k * r ^ Suc i \<and> \<not> r dvd k" if "n \<noteq> 0" "n = m * r" for m
+ proof -
+ from that have "\<bar>m \<bar> < \<bar>n\<bar>"
using \<open>1 < r\<close> by (simp add: abs_mult)
- from less[OF this] n have "\<exists>k i. n = k * r ^ Suc i \<and> \<not> r dvd k" by auto }
+ from less[OF this] that show ?thesis by auto
+ qed
then show ?case
by (metis dvd_def monoid_mult_class.mult.right_neutral mult.commute power_0)
qed
lemma mult_powr_eq_mult_powr_iff_asym:
fixes m1 m2 e1 e2 :: int
- assumes m1: "\<not> 2 dvd m1" and "e1 \<le> e2"
+ assumes m1: "\<not> 2 dvd m1"
+ and "e1 \<le> e2"
shows "m1 * 2 powr e1 = m2 * 2 powr e2 \<longleftrightarrow> m1 = m2 \<and> e1 = e2"
+ (is "?lhs \<longleftrightarrow> ?rhs")
proof
- have "m1 \<noteq> 0" using m1 unfolding dvd_def by auto
- assume eq: "m1 * 2 powr e1 = m2 * 2 powr e2"
- with \<open>e1 \<le> e2\<close> have "m1 = m2 * 2 powr nat (e2 - e1)"
- by (simp add: powr_divide2[symmetric] field_simps)
- also have "\<dots> = m2 * 2^nat (e2 - e1)"
- by (simp add: powr_realpow)
- finally have m1_eq: "m1 = m2 * 2^nat (e2 - e1)"
- unfolding real_of_int_inject .
- with m1 have "m1 = m2"
- by (cases "nat (e2 - e1)") (auto simp add: dvd_def)
- then show "m1 = m2 \<and> e1 = e2"
- using eq \<open>m1 \<noteq> 0\<close> by (simp add: powr_inj)
-qed simp
+ show ?rhs if eq: ?lhs
+ proof -
+ have "m1 \<noteq> 0"
+ using m1 unfolding dvd_def by auto
+ from \<open>e1 \<le> e2\<close> eq have "m1 = m2 * 2 powr nat (e2 - e1)"
+ by (simp add: powr_divide2[symmetric] field_simps)
+ also have "\<dots> = m2 * 2^nat (e2 - e1)"
+ by (simp add: powr_realpow)
+ finally have m1_eq: "m1 = m2 * 2^nat (e2 - e1)"
+ unfolding real_of_int_inject .
+ with m1 have "m1 = m2"
+ by (cases "nat (e2 - e1)") (auto simp add: dvd_def)
+ then show ?thesis
+ using eq \<open>m1 \<noteq> 0\<close> by (simp add: powr_inj)
+ qed
+ show ?lhs if ?rhs
+ using that by simp
+qed
lemma mult_powr_eq_mult_powr_iff:
fixes m1 m2 e1 e2 :: int
@@ -356,16 +405,18 @@
assumes x: "x \<in> float"
obtains (zero) "x = 0"
| (powr) m e :: int where "x = m * 2 powr e" "\<not> 2 dvd m" "x \<noteq> 0"
-proof atomize_elim
- { assume "x \<noteq> 0"
- from x obtain m e :: int where x: "x = m * 2 powr e" by (auto simp: float_def)
+proof -
+ {
+ assume "x \<noteq> 0"
+ from x obtain m e :: int where x: "x = m * 2 powr e"
+ by (auto simp: float_def)
with \<open>x \<noteq> 0\<close> int_cancel_factors[of 2 m] obtain k i where "m = k * 2 ^ i" "\<not> 2 dvd k"
by auto
with \<open>\<not> 2 dvd k\<close> x have "\<exists>(m::int) (e::int). x = m * 2 powr e \<and> \<not> (2::int) dvd m"
by (rule_tac exI[of _ "k"], rule_tac exI[of _ "e + int i"])
- (simp add: powr_add powr_realpow) }
- then show "x = 0 \<or> (\<exists>(m::int) (e::int). x = m * 2 powr e \<and> \<not> (2::int) dvd m \<and> x \<noteq> 0)"
- by blast
+ (simp add: powr_add powr_realpow)
+ }
+ with that show thesis by blast
qed
lemma float_normed_cases:
@@ -373,7 +424,8 @@
obtains (zero) "f = 0"
| (powr) m e :: int where "real f = m * 2 powr e" "\<not> 2 dvd m" "f \<noteq> 0"
proof (atomize_elim, induct f)
- case (float_of y) then show ?case
+ case (float_of y)
+ then show ?case
by (cases rule: floatE_normed) (auto simp: zero_float_def)
qed
@@ -389,7 +441,8 @@
shows exponent_0[simp]: "exponent (float_of 0) = 0" (is ?E)
and mantissa_0[simp]: "mantissa (float_of 0) = 0" (is ?M)
proof -
- have "\<And>p::int \<times> int. fst p = 0 \<and> snd p = 0 \<longleftrightarrow> p = (0, 0)" by auto
+ have "\<And>p::int \<times> int. fst p = 0 \<and> snd p = 0 \<longleftrightarrow> p = (0, 0)"
+ by auto
then show ?E ?M
by (auto simp add: mantissa_def exponent_def zero_float_def)
qed
@@ -398,17 +451,20 @@
shows mantissa_exponent: "real f = mantissa f * 2 powr exponent f" (is ?E)
and mantissa_not_dvd: "f \<noteq> (float_of 0) \<Longrightarrow> \<not> 2 dvd mantissa f" (is "_ \<Longrightarrow> ?D")
proof cases
- assume [simp]: "f \<noteq> (float_of 0)"
+ assume [simp]: "f \<noteq> float_of 0"
have "f = mantissa f * 2 powr exponent f \<and> \<not> 2 dvd mantissa f"
proof (cases f rule: float_normed_cases)
+ case zero
+ then show ?thesis by (simp add: zero_float_def)
+ next
case (powr m e)
- then have "\<exists>p::int \<times> int. (f = 0 \<and> fst p = 0 \<and> snd p = 0)
- \<or> (f \<noteq> 0 \<and> real f = real (fst p) * 2 powr real (snd p) \<and> \<not> 2 dvd fst p)"
+ then have "\<exists>p::int \<times> int. (f = 0 \<and> fst p = 0 \<and> snd p = 0) \<or>
+ (f \<noteq> 0 \<and> real f = real (fst p) * 2 powr real (snd p) \<and> \<not> 2 dvd fst p)"
by auto
then show ?thesis
unfolding exponent_def mantissa_def
by (rule someI2_ex) (simp add: zero_float_def)
- qed (simp add: zero_float_def)
+ qed
then show ?E ?D by auto
qed simp
@@ -422,31 +478,33 @@
shows mantissa_float: "mantissa f = m" (is "?M")
and exponent_float: "m \<noteq> 0 \<Longrightarrow> exponent f = e" (is "_ \<Longrightarrow> ?E")
proof cases
- assume "m = 0" with dvd show "mantissa f = m" by auto
+ assume "m = 0"
+ with dvd show "mantissa f = m" by auto
next
assume "m \<noteq> 0"
then have f_not_0: "f \<noteq> float_of 0" by (simp add: f_def)
- from mantissa_exponent[of f]
- have "m * 2 powr e = mantissa f * 2 powr exponent f"
+ from mantissa_exponent[of f] have "m * 2 powr e = mantissa f * 2 powr exponent f"
by (auto simp add: f_def)
then show "?M" "?E"
using mantissa_not_dvd[OF f_not_0] dvd
by (auto simp: mult_powr_eq_mult_powr_iff)
qed
+
subsection \<open>Compute arithmetic operations\<close>
lemma Float_mantissa_exponent: "Float (mantissa f) (exponent f) = f"
unfolding real_of_float_eq mantissa_exponent[of f] by simp
-lemma Float_cases[case_names Float, cases type: float]:
+lemma Float_cases [cases type: float]:
fixes f :: float
obtains (Float) m e :: int where "f = Float m e"
using Float_mantissa_exponent[symmetric]
by (atomize_elim) auto
lemma denormalize_shift:
- assumes f_def: "f \<equiv> Float m e" and not_0: "f \<noteq> float_of 0"
+ assumes f_def: "f \<equiv> Float m e"
+ and not_0: "f \<noteq> float_of 0"
obtains i where "m = mantissa f * 2 ^ i" "e = exponent f - i"
proof
from mantissa_exponent[of f] f_def
@@ -481,87 +539,75 @@
unfolding real_of_int_inject by auto
qed
-lemma compute_float_zero[code_unfold, code]: "0 = Float 0 0"
- by transfer simp
-hide_fact (open) compute_float_zero
+context
+begin
-lemma compute_float_one[code_unfold, code]: "1 = Float 1 0"
+qualified lemma compute_float_zero[code_unfold, code]: "0 = Float 0 0"
by transfer simp
-hide_fact (open) compute_float_one
+
+qualified lemma compute_float_one[code_unfold, code]: "1 = Float 1 0"
+ by transfer simp
lift_definition normfloat :: "float \<Rightarrow> float" is "\<lambda>x. x" .
lemma normloat_id[simp]: "normfloat x = x" by transfer rule
-lemma compute_normfloat[code]: "normfloat (Float m e) =
+qualified lemma compute_normfloat[code]: "normfloat (Float m e) =
(if m mod 2 = 0 \<and> m \<noteq> 0 then normfloat (Float (m div 2) (e + 1))
else if m = 0 then 0 else Float m e)"
by transfer (auto simp add: powr_add zmod_eq_0_iff)
-hide_fact (open) compute_normfloat
-lemma compute_float_numeral[code_abbrev]: "Float (numeral k) 0 = numeral k"
+qualified lemma compute_float_numeral[code_abbrev]: "Float (numeral k) 0 = numeral k"
by transfer simp
-hide_fact (open) compute_float_numeral
-lemma compute_float_neg_numeral[code_abbrev]: "Float (- numeral k) 0 = - numeral k"
+qualified lemma compute_float_neg_numeral[code_abbrev]: "Float (- numeral k) 0 = - numeral k"
by transfer simp
-hide_fact (open) compute_float_neg_numeral
-lemma compute_float_uminus[code]: "- Float m1 e1 = Float (- m1) e1"
+qualified lemma compute_float_uminus[code]: "- Float m1 e1 = Float (- m1) e1"
by transfer simp
-hide_fact (open) compute_float_uminus
-lemma compute_float_times[code]: "Float m1 e1 * Float m2 e2 = Float (m1 * m2) (e1 + e2)"
+qualified lemma compute_float_times[code]: "Float m1 e1 * Float m2 e2 = Float (m1 * m2) (e1 + e2)"
by transfer (simp add: field_simps powr_add)
-hide_fact (open) compute_float_times
-lemma compute_float_plus[code]: "Float m1 e1 + Float m2 e2 =
+qualified lemma compute_float_plus[code]: "Float m1 e1 + Float m2 e2 =
(if m1 = 0 then Float m2 e2 else if m2 = 0 then Float m1 e1 else
if e1 \<le> e2 then Float (m1 + m2 * 2^nat (e2 - e1)) e1
else Float (m2 + m1 * 2^nat (e1 - e2)) e2)"
by transfer (simp add: field_simps powr_realpow[symmetric] powr_divide2[symmetric])
-hide_fact (open) compute_float_plus
-lemma compute_float_minus[code]: fixes f g::float shows "f - g = f + (-g)"
+qualified lemma compute_float_minus[code]: fixes f g::float shows "f - g = f + (-g)"
by simp
-hide_fact (open) compute_float_minus
-lemma compute_float_sgn[code]: "sgn (Float m1 e1) = (if 0 < m1 then 1 else if m1 < 0 then -1 else 0)"
+qualified lemma compute_float_sgn[code]: "sgn (Float m1 e1) = (if 0 < m1 then 1 else if m1 < 0 then -1 else 0)"
by transfer (simp add: sgn_times)
-hide_fact (open) compute_float_sgn
lift_definition is_float_pos :: "float \<Rightarrow> bool" is "op < 0 :: real \<Rightarrow> bool" .
-lemma compute_is_float_pos[code]: "is_float_pos (Float m e) \<longleftrightarrow> 0 < m"
+qualified lemma compute_is_float_pos[code]: "is_float_pos (Float m e) \<longleftrightarrow> 0 < m"
by transfer (auto simp add: zero_less_mult_iff not_le[symmetric, of _ 0])
-hide_fact (open) compute_is_float_pos
-lemma compute_float_less[code]: "a < b \<longleftrightarrow> is_float_pos (b - a)"
+qualified lemma compute_float_less[code]: "a < b \<longleftrightarrow> is_float_pos (b - a)"
by transfer (simp add: field_simps)
-hide_fact (open) compute_float_less
lift_definition is_float_nonneg :: "float \<Rightarrow> bool" is "op \<le> 0 :: real \<Rightarrow> bool" .
-lemma compute_is_float_nonneg[code]: "is_float_nonneg (Float m e) \<longleftrightarrow> 0 \<le> m"
+qualified lemma compute_is_float_nonneg[code]: "is_float_nonneg (Float m e) \<longleftrightarrow> 0 \<le> m"
by transfer (auto simp add: zero_le_mult_iff not_less[symmetric, of _ 0])
-hide_fact (open) compute_is_float_nonneg
-lemma compute_float_le[code]: "a \<le> b \<longleftrightarrow> is_float_nonneg (b - a)"
+qualified lemma compute_float_le[code]: "a \<le> b \<longleftrightarrow> is_float_nonneg (b - a)"
by transfer (simp add: field_simps)
-hide_fact (open) compute_float_le
lift_definition is_float_zero :: "float \<Rightarrow> bool" is "op = 0 :: real \<Rightarrow> bool" .
-lemma compute_is_float_zero[code]: "is_float_zero (Float m e) \<longleftrightarrow> 0 = m"
+qualified lemma compute_is_float_zero[code]: "is_float_zero (Float m e) \<longleftrightarrow> 0 = m"
by transfer (auto simp add: is_float_zero_def)
-hide_fact (open) compute_is_float_zero
-lemma compute_float_abs[code]: "abs (Float m e) = Float (abs m) e"
+qualified lemma compute_float_abs[code]: "abs (Float m e) = Float (abs m) e"
by transfer (simp add: abs_mult)
-hide_fact (open) compute_float_abs
-lemma compute_float_eq[code]: "equal_class.equal f g = is_float_zero (f - g)"
+qualified lemma compute_float_eq[code]: "equal_class.equal f g = is_float_zero (f - g)"
by transfer simp
-hide_fact (open) compute_float_eq
+
+end
subsection \<open>Lemmas for types @{typ real}, @{typ nat}, @{typ int}\<close>
@@ -590,11 +636,11 @@
subsection \<open>Rounding Real Numbers\<close>
-definition round_down :: "int \<Rightarrow> real \<Rightarrow> real" where
- "round_down prec x = floor (x * 2 powr prec) * 2 powr -prec"
+definition round_down :: "int \<Rightarrow> real \<Rightarrow> real"
+ where "round_down prec x = floor (x * 2 powr prec) * 2 powr -prec"
-definition round_up :: "int \<Rightarrow> real \<Rightarrow> real" where
- "round_up prec x = ceiling (x * 2 powr prec) * 2 powr -prec"
+definition round_up :: "int \<Rightarrow> real \<Rightarrow> real"
+ where "round_up prec x = ceiling (x * 2 powr prec) * 2 powr -prec"
lemma round_down_float[simp]: "round_down prec x \<in> float"
unfolding round_down_def
@@ -692,7 +738,7 @@
from neg have "2 powr real p \<le> 2 powr 0"
by (intro powr_mono) auto
also have "\<dots> \<le> \<lfloor>2 powr 0::real\<rfloor>" by simp
- also have "... \<le> \<lfloor>x * 2 powr (real p)\<rfloor>"
+ also have "\<dots> \<le> \<lfloor>x * 2 powr (real p)\<rfloor>"
unfolding real_of_int_le_iff
using x x_le by (intro floor_mono) (simp add: powr_minus_divide field_simps)
finally show ?thesis
@@ -707,9 +753,11 @@
subsection \<open>Rounding Floats\<close>
-definition div_twopow::"int \<Rightarrow> nat \<Rightarrow> int" where [simp]: "div_twopow x n = x div (2 ^ n)"
+definition div_twopow :: "int \<Rightarrow> nat \<Rightarrow> int"
+ where [simp]: "div_twopow x n = x div (2 ^ n)"
-definition mod_twopow::"int \<Rightarrow> nat \<Rightarrow> int" where [simp]: "mod_twopow x n = x mod (2 ^ n)"
+definition mod_twopow :: "int \<Rightarrow> nat \<Rightarrow> int"
+ where [simp]: "mod_twopow x n = x mod (2 ^ n)"
lemma compute_div_twopow[code]:
"div_twopow x n = (if x = 0 \<or> x = -1 \<or> n = 0 then x else div_twopow (x div 2) (n - 1))"
@@ -722,51 +770,54 @@
lift_definition float_up :: "int \<Rightarrow> float \<Rightarrow> float" is round_up by simp
declare float_up.rep_eq[simp]
-lemma round_up_correct:
- shows "round_up e f - f \<in> {0..2 powr -e}"
-unfolding atLeastAtMost_iff
+lemma round_up_correct: "round_up e f - f \<in> {0..2 powr -e}"
+ unfolding atLeastAtMost_iff
proof
- have "round_up e f - f \<le> round_up e f - round_down e f" using round_down by simp
- also have "\<dots> \<le> 2 powr -e" using round_up_diff_round_down by simp
+ have "round_up e f - f \<le> round_up e f - round_down e f"
+ using round_down by simp
+ also have "\<dots> \<le> 2 powr -e"
+ using round_up_diff_round_down by simp
finally show "round_up e f - f \<le> 2 powr - (real e)"
by simp
qed (simp add: algebra_simps round_up)
-lemma float_up_correct:
- shows "real (float_up e f) - real f \<in> {0..2 powr -e}"
+lemma float_up_correct: "real (float_up e f) - real f \<in> {0..2 powr -e}"
by transfer (rule round_up_correct)
lift_definition float_down :: "int \<Rightarrow> float \<Rightarrow> float" is round_down by simp
declare float_down.rep_eq[simp]
-lemma round_down_correct:
- shows "f - (round_down e f) \<in> {0..2 powr -e}"
-unfolding atLeastAtMost_iff
+lemma round_down_correct: "f - (round_down e f) \<in> {0..2 powr -e}"
+ unfolding atLeastAtMost_iff
proof
- have "f - round_down e f \<le> round_up e f - round_down e f" using round_up by simp
- also have "\<dots> \<le> 2 powr -e" using round_up_diff_round_down by simp
+ have "f - round_down e f \<le> round_up e f - round_down e f"
+ using round_up by simp
+ also have "\<dots> \<le> 2 powr -e"
+ using round_up_diff_round_down by simp
finally show "f - round_down e f \<le> 2 powr - (real e)"
by simp
qed (simp add: algebra_simps round_down)
-lemma float_down_correct:
- shows "real f - real (float_down e f) \<in> {0..2 powr -e}"
+lemma float_down_correct: "real f - real (float_down e f) \<in> {0..2 powr -e}"
by transfer (rule round_down_correct)
-lemma compute_float_down[code]:
+context
+begin
+
+qualified lemma compute_float_down[code]:
"float_down p (Float m e) =
(if p + e < 0 then Float (div_twopow m (nat (-(p + e)))) (-p) else Float m e)"
-proof cases
- assume "p + e < 0"
- hence "real ((2::int) ^ nat (-(p + e))) = 2 powr (-(p + e))"
+proof (cases "p + e < 0")
+ case True
+ then have "real ((2::int) ^ nat (-(p + e))) = 2 powr (-(p + e))"
using powr_realpow[of 2 "nat (-(p + e))"] by simp
- also have "... = 1 / 2 powr p / 2 powr e"
+ also have "\<dots> = 1 / 2 powr p / 2 powr e"
unfolding powr_minus_divide real_of_int_minus by (simp add: powr_add)
finally show ?thesis
using \<open>p + e < 0\<close>
by transfer (simp add: ac_simps round_down_def floor_divide_eq_div[symmetric])
next
- assume "\<not> p + e < 0"
+ case False
then have r: "real e + real p = real (nat (e + p))" by simp
have r: "\<lfloor>(m * 2 powr e) * 2 powr real p\<rfloor> = (m * 2 powr e) * 2 powr real p"
by (auto intro: exI[where x="m*2^nat (e+p)"]
@@ -774,7 +825,6 @@
with \<open>\<not> p + e < 0\<close> show ?thesis
by transfer (auto simp add: round_down_def field_simps powr_add powr_minus)
qed
-hide_fact (open) compute_float_down
lemma abs_round_down_le: "\<bar>f - (round_down e f)\<bar> \<le> 2 powr -e"
using round_down_correct[of f e] by simp
@@ -786,75 +836,100 @@
by (auto simp: round_down_def)
lemma ceil_divide_floor_conv:
-assumes "b \<noteq> 0"
-shows "\<lceil>real a / real b\<rceil> = (if b dvd a then a div b else \<lfloor>real a / real b\<rfloor> + 1)"
-proof cases
- assume "\<not> b dvd a"
- hence "a mod b \<noteq> 0" by auto
- hence ne: "real (a mod b) / real b \<noteq> 0" using \<open>b \<noteq> 0\<close> by auto
+ assumes "b \<noteq> 0"
+ shows "\<lceil>real a / real b\<rceil> = (if b dvd a then a div b else \<lfloor>real a / real b\<rfloor> + 1)"
+proof (cases "b dvd a")
+ case True
+ then show ?thesis
+ by (simp add: ceiling_def real_of_int_minus[symmetric] divide_minus_left[symmetric]
+ floor_divide_eq_div dvd_neg_div del: divide_minus_left real_of_int_minus)
+next
+ case False
+ then have "a mod b \<noteq> 0"
+ by auto
+ then have ne: "real (a mod b) / real b \<noteq> 0"
+ using \<open>b \<noteq> 0\<close> by auto
have "\<lceil>real a / real b\<rceil> = \<lfloor>real a / real b\<rfloor> + 1"
- apply (rule ceiling_eq) apply (auto simp: floor_divide_eq_div[symmetric])
+ apply (rule ceiling_eq)
+ apply (auto simp: floor_divide_eq_div[symmetric])
proof -
- have "real \<lfloor>real a / real b\<rfloor> \<le> real a / real b" by simp
+ have "real \<lfloor>real a / real b\<rfloor> \<le> real a / real b"
+ by simp
moreover have "real \<lfloor>real a / real b\<rfloor> \<noteq> real a / real b"
- apply (subst (2) real_of_int_div_aux) unfolding floor_divide_eq_div using ne \<open>b \<noteq> 0\<close> by auto
+ apply (subst (2) real_of_int_div_aux)
+ unfolding floor_divide_eq_div
+ using ne \<open>b \<noteq> 0\<close> apply auto
+ done
ultimately show "real \<lfloor>real a / real b\<rfloor> < real a / real b" by arith
qed
- thus ?thesis using \<open>\<not> b dvd a\<close> by simp
-qed (simp add: ceiling_def real_of_int_minus[symmetric] divide_minus_left[symmetric]
- floor_divide_eq_div dvd_neg_div del: divide_minus_left real_of_int_minus)
+ then show ?thesis
+ using \<open>\<not> b dvd a\<close> by simp
+qed
-lemma compute_float_up[code]:
- "float_up p x = - float_down p (-x)"
+qualified lemma compute_float_up[code]: "float_up p x = - float_down p (-x)"
by transfer (simp add: round_down_uminus_eq)
-hide_fact (open) compute_float_up
+
+end
subsection \<open>Compute bitlen of integers\<close>
-definition bitlen :: "int \<Rightarrow> int" where
- "bitlen a = (if a > 0 then \<lfloor>log 2 a\<rfloor> + 1 else 0)"
+definition bitlen :: "int \<Rightarrow> int"
+ where "bitlen a = (if a > 0 then \<lfloor>log 2 a\<rfloor> + 1 else 0)"
lemma bitlen_nonneg: "0 \<le> bitlen x"
proof -
- {
- assume "0 > x"
- have "-1 = log 2 (inverse 2)" by (subst log_inverse) simp_all
- also have "... < log 2 (-x)" using \<open>0 > x\<close> by auto
- finally have "-1 < log 2 (-x)" .
- } thus "0 \<le> bitlen x" unfolding bitlen_def by (auto intro!: add_nonneg_nonneg)
+ have "-1 < log 2 (-x)" if "0 > x"
+ proof -
+ have "-1 = log 2 (inverse 2)"
+ by (subst log_inverse) simp_all
+ also have "\<dots> < log 2 (-x)"
+ using \<open>0 > x\<close> by auto
+ finally show ?thesis .
+ qed
+ then show ?thesis
+ unfolding bitlen_def by (auto intro!: add_nonneg_nonneg)
qed
lemma bitlen_bounds:
assumes "x > 0"
shows "2 ^ nat (bitlen x - 1) \<le> x \<and> x < 2 ^ nat (bitlen x)"
proof
- have "(2::real) ^ nat \<lfloor>log 2 (real x)\<rfloor> = 2 powr real (floor (log 2 (real x)))"
- using powr_realpow[symmetric, of 2 "nat \<lfloor>log 2 (real x)\<rfloor>"] \<open>x > 0\<close>
- using real_nat_eq_real[of "floor (log 2 (real x))"]
- by simp
- also have "... \<le> 2 powr log 2 (real x)"
- by simp
- also have "... = real x"
- using \<open>0 < x\<close> by simp
- finally have "2 ^ nat \<lfloor>log 2 (real x)\<rfloor> \<le> real x" by simp
- thus "2 ^ nat (bitlen x - 1) \<le> x" using \<open>x > 0\<close>
- by (simp add: bitlen_def)
-next
- have "x \<le> 2 powr (log 2 x)" using \<open>x > 0\<close> by simp
- also have "... < 2 ^ nat (\<lfloor>log 2 (real x)\<rfloor> + 1)"
- apply (simp add: powr_realpow[symmetric])
- using \<open>x > 0\<close> by simp
- finally show "x < 2 ^ nat (bitlen x)" using \<open>x > 0\<close>
- by (simp add: bitlen_def ac_simps)
+ show "2 ^ nat (bitlen x - 1) \<le> x"
+ proof -
+ have "(2::real) ^ nat \<lfloor>log 2 (real x)\<rfloor> = 2 powr real (floor (log 2 (real x)))"
+ using powr_realpow[symmetric, of 2 "nat \<lfloor>log 2 (real x)\<rfloor>"] \<open>x > 0\<close>
+ using real_nat_eq_real[of "floor (log 2 (real x))"]
+ by simp
+ also have "\<dots> \<le> 2 powr log 2 (real x)"
+ by simp
+ also have "\<dots> = real x"
+ using \<open>0 < x\<close> by simp
+ finally have "2 ^ nat \<lfloor>log 2 (real x)\<rfloor> \<le> real x"
+ by simp
+ then show ?thesis
+ using \<open>0 < x\<close> by (simp add: bitlen_def)
+ qed
+ show "x < 2 ^ nat (bitlen x)"
+ proof -
+ have "x \<le> 2 powr (log 2 x)"
+ using \<open>x > 0\<close> by simp
+ also have "\<dots> < 2 ^ nat (\<lfloor>log 2 (real x)\<rfloor> + 1)"
+ apply (simp add: powr_realpow[symmetric])
+ using \<open>x > 0\<close> apply simp
+ done
+ finally show ?thesis
+ using \<open>x > 0\<close> by (simp add: bitlen_def ac_simps)
+ qed
qed
lemma bitlen_pow2[simp]:
assumes "b > 0"
shows "bitlen (b * 2 ^ c) = bitlen b + c"
proof -
- from assms have "b * 2 ^ c > 0" by auto
- thus ?thesis
+ from assms have "b * 2 ^ c > 0"
+ by auto
+ then show ?thesis
using floor_add[of "log 2 b" c] assms
by (auto simp add: log_mult log_nat_power bitlen_def)
qed
@@ -868,9 +943,9 @@
then show ?thesis by (simp add: f_def bitlen_def Float_def)
next
case False
- hence "f \<noteq> float_of 0"
+ then have "f \<noteq> float_of 0"
unfolding real_of_float_eq by (simp add: f_def)
- hence "mantissa f \<noteq> 0"
+ then have "mantissa f \<noteq> 0"
by (simp add: mantissa_noteq_0)
moreover
obtain i where "m = mantissa f * 2 ^ i" "e = exponent f - int i"
@@ -878,22 +953,27 @@
ultimately show ?thesis by (simp add: abs_mult)
qed
-lemma compute_bitlen[code]:
- shows "bitlen x = (if x > 0 then bitlen (x div 2) + 1 else 0)"
+context
+begin
+
+qualified lemma compute_bitlen[code]: "bitlen x = (if x > 0 then bitlen (x div 2) + 1 else 0)"
proof -
{ assume "2 \<le> x"
then have "\<lfloor>log 2 (x div 2)\<rfloor> + 1 = \<lfloor>log 2 (x - x mod 2)\<rfloor>"
by (simp add: log_mult zmod_zdiv_equality')
also have "\<dots> = \<lfloor>log 2 (real x)\<rfloor>"
- proof cases
- assume "x mod 2 = 0" then show ?thesis by simp
+ proof (cases "x mod 2 = 0")
+ case True
+ then show ?thesis by simp
next
+ case False
def n \<equiv> "\<lfloor>log 2 (real x)\<rfloor>"
then have "0 \<le> n"
using \<open>2 \<le> x\<close> by simp
- assume "x mod 2 \<noteq> 0"
- with \<open>2 \<le> x\<close> have "x mod 2 = 1" "\<not> 2 dvd x" by (auto simp add: dvd_eq_mod_eq_0)
- with \<open>2 \<le> x\<close> have "x \<noteq> 2^nat n" by (cases "nat n") auto
+ from \<open>2 \<le> x\<close> False have "x mod 2 = 1" "\<not> 2 dvd x"
+ by (auto simp add: dvd_eq_mod_eq_0)
+ with \<open>2 \<le> x\<close> have "x \<noteq> 2 ^ nat n"
+ by (cases "nat n") auto
moreover
{ have "real (2^nat n :: int) = 2 powr (nat n)"
by (simp add: powr_realpow)
@@ -922,62 +1002,87 @@
unfolding bitlen_def
by (auto simp: pos_imp_zdiv_pos_iff not_le)
qed
-hide_fact (open) compute_bitlen
+
+end
lemma float_gt1_scale: assumes "1 \<le> Float m e"
shows "0 \<le> e + (bitlen m - 1)"
proof -
have "0 < Float m e" using assms by auto
- hence "0 < m" using powr_gt_zero[of 2 e]
+ then have "0 < m" using powr_gt_zero[of 2 e]
apply (auto simp: zero_less_mult_iff)
- using not_le powr_ge_pzero by blast
- hence "m \<noteq> 0" by auto
+ using not_le powr_ge_pzero apply blast
+ done
+ then have "m \<noteq> 0" by auto
show ?thesis
proof (cases "0 \<le> e")
- case True thus ?thesis using \<open>0 < m\<close> by (simp add: bitlen_def)
+ case True
+ then show ?thesis
+ using \<open>0 < m\<close> by (simp add: bitlen_def)
next
+ case False
have "(1::int) < 2" by simp
- case False let ?S = "2^(nat (-e))"
- have "inverse (2 ^ nat (- e)) = 2 powr e" using assms False powr_realpow[of 2 "nat (-e)"]
+ let ?S = "2^(nat (-e))"
+ have "inverse (2 ^ nat (- e)) = 2 powr e"
+ using assms False powr_realpow[of 2 "nat (-e)"]
by (auto simp: powr_minus field_simps)
- hence "1 \<le> real m * inverse ?S" using assms False powr_realpow[of 2 "nat (-e)"]
+ then have "1 \<le> real m * inverse ?S"
+ using assms False powr_realpow[of 2 "nat (-e)"]
by (auto simp: powr_minus)
- hence "1 * ?S \<le> real m * inverse ?S * ?S" by (rule mult_right_mono, auto)
- hence "?S \<le> real m" unfolding mult.assoc by auto
- hence "?S \<le> m" unfolding real_of_int_le_iff[symmetric] by auto
+ then have "1 * ?S \<le> real m * inverse ?S * ?S"
+ by (rule mult_right_mono) auto
+ then have "?S \<le> real m"
+ unfolding mult.assoc by auto
+ then have "?S \<le> m"
+ unfolding real_of_int_le_iff[symmetric] by auto
from this bitlen_bounds[OF \<open>0 < m\<close>, THEN conjunct2]
- have "nat (-e) < (nat (bitlen m))" unfolding power_strict_increasing_iff[OF \<open>1 < 2\<close>, symmetric]
+ have "nat (-e) < (nat (bitlen m))"
+ unfolding power_strict_increasing_iff[OF \<open>1 < 2\<close>, symmetric]
by (rule order_le_less_trans)
- hence "-e < bitlen m" using False by auto
- thus ?thesis by auto
+ then have "-e < bitlen m"
+ using False by auto
+ then show ?thesis
+ by auto
qed
qed
lemma bitlen_div:
assumes "0 < m"
- shows "1 \<le> real m / 2^nat (bitlen m - 1)" and "real m / 2^nat (bitlen m - 1) < 2"
+ shows "1 \<le> real m / 2^nat (bitlen m - 1)"
+ and "real m / 2^nat (bitlen m - 1) < 2"
proof -
let ?B = "2^nat(bitlen m - 1)"
have "?B \<le> m" using bitlen_bounds[OF \<open>0 <m\<close>] ..
- hence "1 * ?B \<le> real m" unfolding real_of_int_le_iff[symmetric] by auto
- thus "1 \<le> real m / ?B" by auto
+ then have "1 * ?B \<le> real m"
+ unfolding real_of_int_le_iff[symmetric] by auto
+ then show "1 \<le> real m / ?B"
+ by auto
- have "m \<noteq> 0" using assms by auto
- have "0 \<le> bitlen m - 1" using \<open>0 < m\<close> by (auto simp: bitlen_def)
+ have "m \<noteq> 0"
+ using assms by auto
+ have "0 \<le> bitlen m - 1"
+ using \<open>0 < m\<close> by (auto simp: bitlen_def)
- have "m < 2^nat(bitlen m)" using bitlen_bounds[OF \<open>0 <m\<close>] ..
- also have "\<dots> = 2^nat(bitlen m - 1 + 1)" using \<open>0 < m\<close> by (auto simp: bitlen_def)
- also have "\<dots> = ?B * 2" unfolding nat_add_distrib[OF \<open>0 \<le> bitlen m - 1\<close> zero_le_one] by auto
- finally have "real m < 2 * ?B" unfolding real_of_int_less_iff[symmetric] by auto
- hence "real m / ?B < 2 * ?B / ?B" by (rule divide_strict_right_mono, auto)
- thus "real m / ?B < 2" by auto
+ have "m < 2^nat(bitlen m)"
+ using bitlen_bounds[OF \<open>0 <m\<close>] ..
+ also have "\<dots> = 2^nat(bitlen m - 1 + 1)"
+ using \<open>0 < m\<close> by (auto simp: bitlen_def)
+ also have "\<dots> = ?B * 2"
+ unfolding nat_add_distrib[OF \<open>0 \<le> bitlen m - 1\<close> zero_le_one] by auto
+ finally have "real m < 2 * ?B"
+ unfolding real_of_int_less_iff[symmetric] by auto
+ then have "real m / ?B < 2 * ?B / ?B"
+ by (rule divide_strict_right_mono) auto
+ then show "real m / ?B < 2"
+ by auto
qed
+
subsection \<open>Truncating Real Numbers\<close>
-definition truncate_down::"nat \<Rightarrow> real \<Rightarrow> real" where
- "truncate_down prec x = round_down (prec - \<lfloor>log 2 \<bar>x\<bar>\<rfloor> - 1) x"
+definition truncate_down::"nat \<Rightarrow> real \<Rightarrow> real"
+ where "truncate_down prec x = round_down (prec - \<lfloor>log 2 \<bar>x\<bar>\<rfloor> - 1) x"
lemma truncate_down: "truncate_down prec x \<le> x"
using round_down by (simp add: truncate_down_def)
@@ -991,8 +1096,8 @@
lemma truncate_down_float[simp]: "truncate_down p x \<in> float"
by (auto simp: truncate_down_def)
-definition truncate_up::"nat \<Rightarrow> real \<Rightarrow> real" where
- "truncate_up prec x = round_up (prec - \<lfloor>log 2 \<bar>x\<bar>\<rfloor> - 1) x"
+definition truncate_up::"nat \<Rightarrow> real \<Rightarrow> real"
+ where "truncate_up prec x = round_up (prec - \<lfloor>log 2 \<bar>x\<bar>\<rfloor> - 1) x"
lemma truncate_up: "x \<le> truncate_up prec x"
using round_up by (simp add: truncate_up_def)
@@ -1035,22 +1140,28 @@
by (auto simp: truncate_up_def round_up_def intro!: mult_nonpos_nonneg)
lemma truncate_up_le1:
- assumes "x \<le> 1" "1 \<le> p" shows "truncate_up p x \<le> 1"
+ assumes "x \<le> 1" "1 \<le> p"
+ shows "truncate_up p x \<le> 1"
proof -
- {
- assume "x \<le> 0"
- with truncate_up_nonpos[OF this, of p] have ?thesis by simp
- } moreover {
- assume "x > 0"
- hence le: "\<lfloor>log 2 \<bar>x\<bar>\<rfloor> \<le> 0"
+ consider "x \<le> 0" | "x > 0"
+ by arith
+ then show ?thesis
+ proof cases
+ case 1
+ with truncate_up_nonpos[OF this, of p] show ?thesis
+ by simp
+ next
+ case 2
+ then have le: "\<lfloor>log 2 \<bar>x\<bar>\<rfloor> \<le> 0"
using assms by (auto simp: log_less_iff)
from assms have "1 \<le> int p" by simp
from add_mono[OF this le]
- have ?thesis using assms
- by (simp add: truncate_up_def round_up_le1 add_mono)
- } ultimately show ?thesis by arith
+ show ?thesis
+ using assms by (simp add: truncate_up_def round_up_le1 add_mono)
+ qed
qed
+
subsection \<open>Truncating Floats\<close>
lift_definition float_round_up :: "nat \<Rightarrow> float \<Rightarrow> float" is truncate_up
@@ -1078,25 +1189,30 @@
and minus_float_round_down_eq: "- float_round_down prec x = float_round_up prec (- x)"
by (transfer, simp add: truncate_down_uminus_eq truncate_up_uminus_eq)+
-lemma compute_float_round_down[code]:
+context
+begin
+
+qualified lemma compute_float_round_down[code]:
"float_round_down prec (Float m e) = (let d = bitlen (abs m) - int prec in
if 0 < d then Float (div_twopow m (nat d)) (e + d)
else Float m e)"
using Float.compute_float_down[of "prec - bitlen \<bar>m\<bar> - e" m e, symmetric]
by transfer (simp add: field_simps abs_mult log_mult bitlen_def truncate_down_def
cong del: if_weak_cong)
-hide_fact (open) compute_float_round_down
-lemma compute_float_round_up[code]:
+qualified lemma compute_float_round_up[code]:
"float_round_up prec x = - float_round_down prec (-x)"
by transfer (simp add: truncate_down_uminus_eq)
-hide_fact (open) compute_float_round_up
+
+end
subsection \<open>Approximation of positive rationals\<close>
-lemma div_mult_twopow_eq: fixes a b::nat shows "a div ((2::nat) ^ n) div b = a div (b * 2 ^ n)"
- by (cases "b=0") (simp_all add: div_mult2_eq[symmetric] ac_simps)
+lemma div_mult_twopow_eq:
+ fixes a b :: nat
+ shows "a div ((2::nat) ^ n) div b = a div (b * 2 ^ n)"
+ by (cases "b = 0") (simp_all add: div_mult2_eq[symmetric] ac_simps)
lemma real_div_nat_eq_floor_of_divide:
fixes a b :: nat
@@ -1106,23 +1222,29 @@
definition "rat_precision prec x y = int prec - (bitlen x - bitlen y)"
lift_definition lapprox_posrat :: "nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> float"
- is "\<lambda>prec (x::nat) (y::nat). round_down (rat_precision prec x y) (x / y)" by simp
+ is "\<lambda>prec (x::nat) (y::nat). round_down (rat_precision prec x y) (x / y)"
+ by simp
-lemma compute_lapprox_posrat[code]:
+context
+begin
+
+qualified lemma compute_lapprox_posrat[code]:
fixes prec x y
shows "lapprox_posrat prec x y =
(let
- l = rat_precision prec x y;
- d = if 0 \<le> l then x * 2^nat l div y else x div 2^nat (- l) div y
+ l = rat_precision prec x y;
+ d = if 0 \<le> l then x * 2^nat l div y else x div 2^nat (- l) div y
in normfloat (Float d (- l)))"
unfolding div_mult_twopow_eq
by transfer
(simp add: round_down_def powr_int real_div_nat_eq_floor_of_divide field_simps Let_def
del: two_powr_minus_int_float)
-hide_fact (open) compute_lapprox_posrat
+
+end
lift_definition rapprox_posrat :: "nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> float"
- is "\<lambda>prec (x::nat) (y::nat). round_up (rat_precision prec x y) (x / y)" by simp
+ is "\<lambda>prec (x::nat) (y::nat). round_up (rat_precision prec x y) (x / y)" by
+ simp
context
notes divmod_int_mod_div[simp]
@@ -1137,14 +1259,16 @@
(d, m) = divmod_int (fst X) (snd X)
in normfloat (Float (d + (if m = 0 \<or> y = 0 then 0 else 1)) (- l)))"
proof (cases "y = 0")
- assume "y = 0" thus ?thesis by transfer simp
+ assume "y = 0"
+ then show ?thesis by transfer simp
next
assume "y \<noteq> 0"
show ?thesis
proof (cases "0 \<le> l")
- assume "0 \<le> l"
+ case True
def x' \<equiv> "x * 2 ^ nat l"
- have "int x * 2 ^ nat l = x'" by (simp add: x'_def int_mult int_power)
+ have "int x * 2 ^ nat l = x'"
+ by (simp add: x'_def int_mult int_power)
moreover have "real x * 2 powr real l = real x'"
by (simp add: powr_realpow[symmetric] \<open>0 \<le> l\<close> x'_def)
ultimately show ?thesis
@@ -1152,7 +1276,7 @@
l_def[symmetric, THEN meta_eq_to_obj_eq]
by transfer (auto simp add: floor_divide_eq_div [symmetric] round_up_def)
next
- assume "\<not> 0 \<le> l"
+ case False
def y' \<equiv> "y * 2 ^ nat (- l)"
from \<open>y \<noteq> 0\<close> have "y' \<noteq> 0" by (simp add: y'_def)
have "int y * 2 ^ nat (- l) = y'" by (simp add: y'_def int_mult int_power)
@@ -1170,38 +1294,48 @@
end
lemma rat_precision_pos:
- assumes "0 \<le> x" and "0 < y" and "2 * x < y" and "0 < n"
+ assumes "0 \<le> x"
+ and "0 < y"
+ and "2 * x < y"
+ and "0 < n"
shows "rat_precision n (int x) (int y) > 0"
proof -
- { assume "0 < x" hence "log 2 x + 1 = log 2 (2 * x)" by (simp add: log_mult) }
- hence "bitlen (int x) < bitlen (int y)" using assms
+ have "0 < x \<Longrightarrow> log 2 x + 1 = log 2 (2 * x)"
+ by (simp add: log_mult)
+ then have "bitlen (int x) < bitlen (int y)"
+ using assms
by (simp add: bitlen_def del: floor_add_one)
(auto intro!: floor_mono simp add: floor_add_one[symmetric] simp del: floor_add floor_add_one)
- thus ?thesis
- using assms by (auto intro!: pos_add_strict simp add: field_simps rat_precision_def)
+ then show ?thesis
+ using assms
+ by (auto intro!: pos_add_strict simp add: field_simps rat_precision_def)
qed
lemma rapprox_posrat_less1:
- shows "0 \<le> x \<Longrightarrow> 0 < y \<Longrightarrow> 2 * x < y \<Longrightarrow> 0 < n \<Longrightarrow> real (rapprox_posrat n x y) < 1"
+ "0 \<le> x \<Longrightarrow> 0 < y \<Longrightarrow> 2 * x < y \<Longrightarrow> 0 < n \<Longrightarrow> real (rapprox_posrat n x y) < 1"
by transfer (simp add: rat_precision_pos round_up_less1)
lift_definition lapprox_rat :: "nat \<Rightarrow> int \<Rightarrow> int \<Rightarrow> float" is
- "\<lambda>prec (x::int) (y::int). round_down (rat_precision prec \<bar>x\<bar> \<bar>y\<bar>) (x / y)" by simp
+ "\<lambda>prec (x::int) (y::int). round_down (rat_precision prec \<bar>x\<bar> \<bar>y\<bar>) (x / y)"
+ by simp
-lemma compute_lapprox_rat[code]:
+context
+begin
+
+qualified lemma compute_lapprox_rat[code]:
"lapprox_rat prec x y =
- (if y = 0 then 0
+ (if y = 0 then 0
else if 0 \<le> x then
- (if 0 < y then lapprox_posrat prec (nat x) (nat y)
+ (if 0 < y then lapprox_posrat prec (nat x) (nat y)
else - (rapprox_posrat prec (nat x) (nat (-y))))
else (if 0 < y
then - (rapprox_posrat prec (nat (-x)) (nat y))
else lapprox_posrat prec (nat (-x)) (nat (-y))))"
by transfer (auto simp: round_up_def round_down_def ceiling_def ac_simps)
-hide_fact (open) compute_lapprox_rat
lift_definition rapprox_rat :: "nat \<Rightarrow> int \<Rightarrow> int \<Rightarrow> float" is
- "\<lambda>prec (x::int) (y::int). round_up (rat_precision prec \<bar>x\<bar> \<bar>y\<bar>) (x / y)" by simp
+ "\<lambda>prec (x::int) (y::int). round_up (rat_precision prec \<bar>x\<bar> \<bar>y\<bar>) (x / y)"
+ by simp
lemma "rapprox_rat = rapprox_posrat"
by transfer auto
@@ -1209,10 +1343,12 @@
lemma "lapprox_rat = lapprox_posrat"
by transfer auto
-lemma compute_rapprox_rat[code]:
+qualified lemma compute_rapprox_rat[code]:
"rapprox_rat prec x y = - lapprox_rat prec (-x) y"
by transfer (simp add: round_down_uminus_eq)
-hide_fact (open) compute_rapprox_rat
+
+end
+
subsection \<open>Division\<close>
@@ -1223,47 +1359,58 @@
lift_definition float_divl :: "nat \<Rightarrow> float \<Rightarrow> float \<Rightarrow> float" is real_divl
by (simp add: real_divl_def)
-lemma compute_float_divl[code]:
+context
+begin
+
+qualified lemma compute_float_divl[code]:
"float_divl prec (Float m1 s1) (Float m2 s2) = lapprox_rat prec m1 m2 * Float 1 (s1 - s2)"
-proof cases
+proof (cases "m1 \<noteq> 0 \<and> m2 \<noteq> 0")
+ case True
let ?f1 = "real m1 * 2 powr real s1" and ?f2 = "real m2 * 2 powr real s2"
let ?m = "real m1 / real m2" and ?s = "2 powr real (s1 - s2)"
- assume not_0: "m1 \<noteq> 0 \<and> m2 \<noteq> 0"
- then have eq2: "(int prec + \<lfloor>log 2 \<bar>?f2\<bar>\<rfloor> - \<lfloor>log 2 \<bar>?f1\<bar>\<rfloor>) = rat_precision prec \<bar>m1\<bar> \<bar>m2\<bar> + (s2 - s1)"
+ from True have eq2: "(int prec + \<lfloor>log 2 \<bar>?f2\<bar>\<rfloor> - \<lfloor>log 2 \<bar>?f1\<bar>\<rfloor>) =
+ rat_precision prec \<bar>m1\<bar> \<bar>m2\<bar> + (s2 - s1)"
by (simp add: abs_mult log_mult rat_precision_def bitlen_def)
have eq1: "real m1 * 2 powr real s1 / (real m2 * 2 powr real s2) = ?m * ?s"
by (simp add: field_simps powr_divide2[symmetric])
-
- show ?thesis
- using not_0
+ from True show ?thesis
by (transfer fixing: m1 s1 m2 s2 prec) (unfold eq1 eq2 round_down_shift real_divl_def,
simp add: field_simps)
-qed (transfer, auto simp: real_divl_def)
-hide_fact (open) compute_float_divl
+next
+ case False
+ then show ?thesis by transfer (auto simp: real_divl_def)
+qed
lift_definition float_divr :: "nat \<Rightarrow> float \<Rightarrow> float \<Rightarrow> float" is real_divr
by (simp add: real_divr_def)
-lemma compute_float_divr[code]:
+qualified lemma compute_float_divr[code]:
"float_divr prec x y = - float_divl prec (-x) y"
by transfer (simp add: real_divr_def real_divl_def round_down_uminus_eq)
-hide_fact (open) compute_float_divr
+
+end
subsection \<open>Approximate Power\<close>
-lemma div2_less_self[termination_simp]: fixes n::nat shows "odd n \<Longrightarrow> n div 2 < n"
+lemma div2_less_self[termination_simp]:
+ fixes n :: nat
+ shows "odd n \<Longrightarrow> n div 2 < n"
by (simp add: odd_pos)
-fun power_down :: "nat \<Rightarrow> real \<Rightarrow> nat \<Rightarrow> real" where
+fun power_down :: "nat \<Rightarrow> real \<Rightarrow> nat \<Rightarrow> real"
+where
"power_down p x 0 = 1"
| "power_down p x (Suc n) =
- (if odd n then truncate_down (Suc p) ((power_down p x (Suc n div 2))\<^sup>2) else truncate_down (Suc p) (x * power_down p x n))"
+ (if odd n then truncate_down (Suc p) ((power_down p x (Suc n div 2))\<^sup>2)
+ else truncate_down (Suc p) (x * power_down p x n))"
-fun power_up :: "nat \<Rightarrow> real \<Rightarrow> nat \<Rightarrow> real" where
+fun power_up :: "nat \<Rightarrow> real \<Rightarrow> nat \<Rightarrow> real"
+where
"power_up p x 0 = 1"
| "power_up p x (Suc n) =
- (if odd n then truncate_up p ((power_up p x (Suc n div 2))\<^sup>2) else truncate_up p (x * power_up p x n))"
+ (if odd n then truncate_up p ((power_up p x (Suc n div 2))\<^sup>2)
+ else truncate_up p (x * power_up p x n))"
lift_definition power_up_fl :: "nat \<Rightarrow> float \<Rightarrow> nat \<Rightarrow> float" is power_up
by (induct_tac rule: power_up.induct) simp_all
@@ -1279,11 +1426,13 @@
lemma compute_power_up_fl[code]:
"power_up_fl p x 0 = 1"
"power_up_fl p x (Suc n) =
- (if odd n then float_round_up p ((power_up_fl p x (Suc n div 2))\<^sup>2) else float_round_up p (x * power_up_fl p x n))"
+ (if odd n then float_round_up p ((power_up_fl p x (Suc n div 2))\<^sup>2)
+ else float_round_up p (x * power_up_fl p x n))"
and compute_power_down_fl[code]:
"power_down_fl p x 0 = 1"
"power_down_fl p x (Suc n) =
- (if odd n then float_round_down (Suc p) ((power_down_fl p x (Suc n div 2))\<^sup>2) else float_round_down (Suc p) (x * power_down_fl p x n))"
+ (if odd n then float_round_down (Suc p) ((power_down_fl p x (Suc n div 2))\<^sup>2)
+ else float_round_down (Suc p) (x * power_down_fl p x n))"
unfolding atomize_conj
by transfer simp
@@ -1300,7 +1449,7 @@
case (2 p x n)
{
assume "odd n"
- hence "(power_down p x (Suc n div 2)) ^ 2 \<le> (x ^ (Suc n div 2)) ^ 2"
+ then have "(power_down p x (Suc n div 2)) ^ 2 \<le> (x ^ (Suc n div 2)) ^ 2"
using 2
by (auto intro: power_mono power_down_nonneg simp del: odd_Suc_div_two)
also have "\<dots> = x ^ (Suc n div 2 * 2)"
@@ -1310,7 +1459,8 @@
finally have ?case
using \<open>odd n\<close>
by (auto intro!: truncate_down_le simp del: odd_Suc_div_two)
- } thus ?case
+ }
+ then show ?case
by (auto intro!: truncate_down_le mult_left_mono 2 mult_nonneg_nonneg power_down_nonneg)
qed simp
@@ -1319,9 +1469,9 @@
case (2 p x n)
{
assume "odd n"
- hence "Suc n = Suc n div 2 * 2"
+ then have "Suc n = Suc n div 2 * 2"
using \<open>odd n\<close> even_Suc by presburger
- hence "x ^ Suc n \<le> (x ^ (Suc n div 2))\<^sup>2"
+ then have "x ^ Suc n \<le> (x ^ (Suc n div 2))\<^sup>2"
by (simp add: power_mult[symmetric])
also have "\<dots> \<le> (power_up p x (Suc n div 2))\<^sup>2"
using 2 \<open>odd n\<close>
@@ -1329,7 +1479,8 @@
finally have ?case
using \<open>odd n\<close>
by (auto intro!: truncate_up_le simp del: odd_Suc_div_two )
- } thus ?case
+ }
+ then show ?case
by (auto intro!: truncate_up_le mult_left_mono 2)
qed simp
@@ -1383,8 +1534,7 @@
using truncate_down_uminus_eq[of p "x + y"]
by (auto simp: plus_down_def plus_up_def)
-lemma
- truncate_down_log2_eqI:
+lemma truncate_down_log2_eqI:
assumes "\<lfloor>log 2 \<bar>x\<bar>\<rfloor> = \<lfloor>log 2 \<bar>y\<bar>\<rfloor>"
assumes "\<lfloor>x * 2 powr (p - \<lfloor>log 2 \<bar>x\<bar>\<rfloor> - 1)\<rfloor> = \<lfloor>y * 2 powr (p - \<lfloor>log 2 \<bar>x\<bar>\<rfloor> - 1)\<rfloor>"
shows "truncate_down p x = truncate_down p y"
@@ -1395,40 +1545,43 @@
(metis Float.compute_bitlen add.commute bitlen_def bitlen_nonneg less_add_same_cancel2 not_less
zero_less_one)
-lemma
- sum_neq_zeroI:
- fixes a k::real
+lemma sum_neq_zeroI:
+ fixes a k :: real
shows "abs a \<ge> k \<Longrightarrow> abs b < k \<Longrightarrow> a + b \<noteq> 0"
and "abs a > k \<Longrightarrow> abs b \<le> k \<Longrightarrow> a + b \<noteq> 0"
by auto
-lemma
- abs_real_le_2_powr_bitlen[simp]:
- "\<bar>real m2\<bar> < 2 powr real (bitlen \<bar>m2\<bar>)"
-proof cases
- assume "m2 \<noteq> 0"
- hence "\<bar>m2\<bar> < 2 ^ nat (bitlen \<bar>m2\<bar>)"
+lemma abs_real_le_2_powr_bitlen[simp]: "\<bar>real m2\<bar> < 2 powr real (bitlen \<bar>m2\<bar>)"
+proof (cases "m2 = 0")
+ case True
+ then show ?thesis by simp
+next
+ case False
+ then have "\<bar>m2\<bar> < 2 ^ nat (bitlen \<bar>m2\<bar>)"
using bitlen_bounds[of "\<bar>m2\<bar>"]
by (auto simp: powr_add bitlen_nonneg)
- thus ?thesis
+ then show ?thesis
by (simp add: powr_int bitlen_nonneg real_of_int_less_iff[symmetric])
-qed simp
+qed
lemma floor_sum_times_2_powr_sgn_eq:
- fixes ai p q::int
- and a b::real
+ fixes ai p q :: int
+ and a b :: real
assumes "a * 2 powr p = ai"
- assumes b_le_1: "abs (b * 2 powr (p + 1)) \<le> 1"
- assumes leqp: "q \<le> p"
+ and b_le_1: "abs (b * 2 powr (p + 1)) \<le> 1"
+ and leqp: "q \<le> p"
shows "\<lfloor>(a + b) * 2 powr q\<rfloor> = \<lfloor>(2 * ai + sgn b) * 2 powr (q - p - 1)\<rfloor>"
proof -
- {
- assume "b = 0"
- hence ?thesis
+ consider "b = 0" | "b > 0" | "b < 0" by arith
+ then show ?thesis
+ proof cases
+ case 1
+ then show ?thesis
by (simp add: assms(1)[symmetric] powr_add[symmetric] algebra_simps powr_mult_base)
- } moreover {
- assume "b > 0"
- hence "b * 2 powr p < abs (b * 2 powr (p + 1))" by simp
+ next
+ case 2
+ then have "b * 2 powr p < abs (b * 2 powr (p + 1))"
+ by simp
also note b_le_1
finally have b_less_1: "b * 2 powr real p < 1" .
@@ -1455,13 +1608,12 @@
by (simp del: real_of_int_power add: floor_divide_real_eq_div floor_eq)
finally
have "\<lfloor>(2 * ai + (sgn b)) * 2 powr (real (q - p) - 1)\<rfloor> =
- \<lfloor>real ai / real ((2::int) ^ nat (p - q))\<rfloor>"
- .
- } ultimately have ?thesis by simp
- } moreover {
- assume "\<not> 0 \<le> b"
- hence "0 > b" by simp
- hence floor_eq: "\<lfloor>b * 2 powr (real p + 1)\<rfloor> = -1"
+ \<lfloor>real ai / real ((2::int) ^ nat (p - q))\<rfloor>" .
+ }
+ ultimately show ?thesis by simp
+ next
+ case 3
+ then have floor_eq: "\<lfloor>b * 2 powr (real p + 1)\<rfloor> = -1"
using b_le_1
by (auto simp: floor_eq_iff algebra_simps pos_divide_le_eq[symmetric] abs_if divide_powr_uminus
intro!: mult_neg_pos split: split_if_asm)
@@ -1479,22 +1631,26 @@
del: real_of_int_mult real_of_int_power real_of_int_diff)
also have "\<dots> = \<lfloor>(2 * ai - 1) * 2 powr (q - p - 1)\<rfloor>"
using assms by (simp add: algebra_simps divide_powr_uminus powr_realpow[symmetric])
- finally have ?thesis using \<open>b < 0\<close> by simp
- } ultimately show ?thesis by arith
+ finally show ?thesis
+ using \<open>b < 0\<close> by simp
+ qed
qed
-lemma
- log2_abs_int_add_less_half_sgn_eq:
- fixes ai::int and b::real
- assumes "abs b \<le> 1/2" "ai \<noteq> 0"
+lemma log2_abs_int_add_less_half_sgn_eq:
+ fixes ai :: int
+ and b :: real
+ assumes "abs b \<le> 1/2"
+ and "ai \<noteq> 0"
shows "\<lfloor>log 2 \<bar>real ai + b\<bar>\<rfloor> = \<lfloor>log 2 \<bar>ai + sgn b / 2\<bar>\<rfloor>"
-proof cases
- assume "b = 0" thus ?thesis by simp
+proof (cases "b = 0")
+ case True
+ then show ?thesis by simp
next
- assume "b \<noteq> 0"
+ case False
def k \<equiv> "\<lfloor>log 2 \<bar>ai\<bar>\<rfloor>"
- hence "\<lfloor>log 2 \<bar>ai\<bar>\<rfloor> = k" by simp
- hence k: "2 powr k \<le> \<bar>ai\<bar>" "\<bar>ai\<bar> < 2 powr (k + 1)"
+ then have "\<lfloor>log 2 \<bar>ai\<bar>\<rfloor> = k"
+ by simp
+ then have k: "2 powr k \<le> \<bar>ai\<bar>" "\<bar>ai\<bar> < 2 powr (k + 1)"
by (simp_all add: floor_log_eq_powr_iff \<open>ai \<noteq> 0\<close>)
have "k \<ge> 0"
using assms by (auto simp: k_def)
@@ -1502,7 +1658,7 @@
have r: "0 \<le> r" "r < 2 powr k"
using \<open>k \<ge> 0\<close> k
by (auto simp: r_def k_def algebra_simps powr_add abs_if powr_int)
- hence "r \<le> (2::int) ^ nat k - 1"
+ then have "r \<le> (2::int) ^ nat k - 1"
using \<open>k \<ge> 0\<close> by (auto simp: powr_int)
from this[simplified real_of_int_le_iff[symmetric]] \<open>0 \<le> k\<close>
have r_le: "r \<le> 2 powr k - 1"
@@ -1511,7 +1667,7 @@
have "\<bar>ai\<bar> = 2 powr k + r"
using \<open>k \<ge> 0\<close> by (auto simp: k_def r_def powr_realpow[symmetric])
- have pos: "\<And>b::real. abs b < 1 \<Longrightarrow> 0 < 2 powr k + (r + b)"
+ have pos: "abs b < 1 \<Longrightarrow> 0 < 2 powr k + (r + b)" for b :: real
using \<open>0 \<le> k\<close> \<open>ai \<noteq> 0\<close>
by (auto simp add: r_def powr_realpow[symmetric] abs_if sgn_if algebra_simps
split: split_if_asm)
@@ -1557,8 +1713,12 @@
finally show ?thesis .
qed
-lemma compute_far_float_plus_down:
- fixes m1 e1 m2 e2::int and p::nat
+context
+begin
+
+qualified lemma compute_far_float_plus_down:
+ fixes m1 e1 m2 e2 :: int
+ and p :: nat
defines "k1 \<equiv> p - nat (bitlen \<bar>m1\<bar>)"
assumes H: "bitlen \<bar>m2\<bar> \<le> e1 - e2 - k1 - 2" "m1 \<noteq> 0" "m2 \<noteq> 0" "e1 \<ge> e2"
shows "float_plus_down p (Float m1 e1) (Float m2 e2) =
@@ -1584,7 +1744,7 @@
finally have abs_m2_less_half: "\<bar>?m2\<bar> < 1 / 2"
by simp
- hence "\<bar>real m2\<bar> < 2 powr -(?shift + 1)"
+ then have "\<bar>real m2\<bar> < 2 powr -(?shift + 1)"
unfolding powr_minus_divide by (auto simp: bitlen_def field_simps powr_mult_base abs_mult)
also have "\<dots> \<le> 2 powr real (e1 - e2 - 2)"
by simp
@@ -1593,7 +1753,7 @@
also have "1/4 < \<bar>real m1\<bar> / 2" using \<open>m1 \<noteq> 0\<close> by simp
finally have b_less_half_a: "\<bar>?b\<bar> < 1/2 * \<bar>?a\<bar>"
by (simp add: algebra_simps powr_mult_base abs_mult)
- hence a_half_less_sum: "\<bar>?a\<bar> / 2 < \<bar>?sum\<bar>"
+ then have a_half_less_sum: "\<bar>?a\<bar> / 2 < \<bar>?sum\<bar>"
by (auto simp: field_simps abs_if split: split_if_asm)
from b_less_half_a have "\<bar>?b\<bar> < \<bar>?a\<bar>" "\<bar>?b\<bar> \<le> \<bar>?a\<bar>"
@@ -1602,14 +1762,14 @@
have "\<bar>real (Float m1 e1)\<bar> \<ge> 1/4 * 2 powr real e1"
using \<open>m1 \<noteq> 0\<close>
by (auto simp: powr_add powr_int bitlen_nonneg divide_right_mono abs_mult)
- hence "?sum \<noteq> 0" using b_less_quarter
+ then have "?sum \<noteq> 0" using b_less_quarter
by (rule sum_neq_zeroI)
- hence "?m1 + ?m2 \<noteq> 0"
+ then have "?m1 + ?m2 \<noteq> 0"
unfolding sum_eq by (simp add: abs_mult zero_less_mult_iff)
have "\<bar>real ?m1\<bar> \<ge> 2 ^ Suc k1" "\<bar>?m2'\<bar> < 2 ^ Suc k1"
using \<open>m1 \<noteq> 0\<close> \<open>m2 \<noteq> 0\<close> by (auto simp: sgn_if less_1_mult abs_mult simp del: power.simps)
- hence sum'_nz: "?m1 + ?m2' \<noteq> 0"
+ then have sum'_nz: "?m1 + ?m2' \<noteq> 0"
by (intro sum_neq_zeroI)
have "\<lfloor>log 2 \<bar>real (Float m1 e1) + real (Float m2 e2)\<bar>\<rfloor> = \<lfloor>log 2 \<bar>?m1 + ?m2\<bar>\<rfloor> + ?e"
@@ -1624,13 +1784,13 @@
also
have "\<bar>?m1 + ?m2'\<bar> * 2 powr ?e = \<bar>?m1 * 2 + sgn m2\<bar> * 2 powr (?e - 1)"
by (auto simp: field_simps powr_minus[symmetric] powr_divide2[symmetric] powr_mult_base)
- hence "\<lfloor>log 2 \<bar>?m1 + ?m2'\<bar>\<rfloor> + ?e = \<lfloor>log 2 \<bar>real (Float (?m1 * 2 + sgn m2) (?e - 1))\<bar>\<rfloor>"
+ then have "\<lfloor>log 2 \<bar>?m1 + ?m2'\<bar>\<rfloor> + ?e = \<lfloor>log 2 \<bar>real (Float (?m1 * 2 + sgn m2) (?e - 1))\<bar>\<rfloor>"
using \<open>?m1 + ?m2' \<noteq> 0\<close>
unfolding floor_add[symmetric]
by (simp add: log_add_eq_powr abs_mult_pos)
finally
have "\<lfloor>log 2 \<bar>?sum\<bar>\<rfloor> = \<lfloor>log 2 \<bar>real (Float (?m1*2 + sgn m2) (?e - 1))\<bar>\<rfloor>" .
- hence "plus_down p (Float m1 e1) (Float m2 e2) =
+ then have "plus_down p (Float m1 e1) (Float m2 e2) =
truncate_down p (Float (?m1*2 + sgn m2) (?e - 1))"
unfolding plus_down_def
proof (rule truncate_down_log2_eqI)
@@ -1668,14 +1828,14 @@
finally
show "\<lfloor>(?a + ?b) * 2 powr ?f\<rfloor> = \<lfloor>real (Float (?m1 * 2 + sgn m2) (?e - 1)) * 2 powr ?f\<rfloor>" .
qed
- thus ?thesis
+ then show ?thesis
by transfer (simp add: plus_down_def ac_simps Let_def)
qed
lemma compute_float_plus_down_naive[code]: "float_plus_down p x y = float_round_down p (x + y)"
by transfer (auto simp: plus_down_def)
-lemma compute_float_plus_down[code]:
+qualified lemma compute_float_plus_down[code]:
fixes p::nat and m1 e1 m2 e2::int
shows "float_plus_down p (Float m1 e1) (Float m2 e2) =
(if m1 = 0 then float_round_down p (Float m2 e2)
@@ -1689,53 +1849,66 @@
else float_plus_down p (Float m2 e2) (Float m1 e1)))"
proof -
{
- assume H: "bitlen \<bar>m2\<bar> \<le> e1 - e2 - (p - nat (bitlen \<bar>m1\<bar>)) - 2" "m1 \<noteq> 0" "m2 \<noteq> 0" "e1 \<ge> e2"
- note compute_far_float_plus_down[OF H]
+ assume "bitlen \<bar>m2\<bar> \<le> e1 - e2 - (p - nat (bitlen \<bar>m1\<bar>)) - 2" "m1 \<noteq> 0" "m2 \<noteq> 0" "e1 \<ge> e2"
+ note compute_far_float_plus_down[OF this]
}
- thus ?thesis
+ then show ?thesis
by transfer (simp add: Let_def plus_down_def ac_simps)
qed
-hide_fact (open) compute_far_float_plus_down
-hide_fact (open) compute_float_plus_down
-lemma compute_float_plus_up[code]: "float_plus_up p x y = - float_plus_down p (-x) (-y)"
+qualified lemma compute_float_plus_up[code]: "float_plus_up p x y = - float_plus_down p (-x) (-y)"
using truncate_down_uminus_eq[of p "x + y"]
by transfer (simp add: plus_down_def plus_up_def ac_simps)
-hide_fact (open) compute_float_plus_up
lemma mantissa_zero[simp]: "mantissa 0 = 0"
-by (metis mantissa_0 zero_float.abs_eq)
+ by (metis mantissa_0 zero_float.abs_eq)
+
+end
subsection \<open>Lemmas needed by Approximate\<close>
-lemma Float_num[simp]: shows
- "real (Float 1 0) = 1" and "real (Float 1 1) = 2" and "real (Float 1 2) = 4" and
- "real (Float 1 (- 1)) = 1/2" and "real (Float 1 (- 2)) = 1/4" and "real (Float 1 (- 3)) = 1/8" and
- "real (Float (- 1) 0) = -1" and "real (Float (number_of n) 0) = number_of n"
-using two_powr_int_float[of 2] two_powr_int_float[of "-1"] two_powr_int_float[of "-2"] two_powr_int_float[of "-3"]
-using powr_realpow[of 2 2] powr_realpow[of 2 3]
-using powr_minus[of 2 1] powr_minus[of 2 2] powr_minus[of 2 3]
-by auto
+lemma Float_num[simp]:
+ "real (Float 1 0) = 1"
+ "real (Float 1 1) = 2"
+ "real (Float 1 2) = 4"
+ "real (Float 1 (- 1)) = 1/2"
+ "real (Float 1 (- 2)) = 1/4"
+ "real (Float 1 (- 3)) = 1/8"
+ "real (Float (- 1) 0) = -1"
+ "real (Float (number_of n) 0) = number_of n"
+ using two_powr_int_float[of 2] two_powr_int_float[of "-1"] two_powr_int_float[of "-2"]
+ two_powr_int_float[of "-3"]
+ using powr_realpow[of 2 2] powr_realpow[of 2 3]
+ using powr_minus[of 2 1] powr_minus[of 2 2] powr_minus[of 2 3]
+ by auto
-lemma real_of_Float_int[simp]: "real (Float n 0) = real n" by simp
+lemma real_of_Float_int[simp]: "real (Float n 0) = real n"
+ by simp
-lemma float_zero[simp]: "real (Float 0 e) = 0" by simp
+lemma float_zero[simp]: "real (Float 0 e) = 0"
+ by simp
lemma abs_div_2_less: "a \<noteq> 0 \<Longrightarrow> a \<noteq> -1 \<Longrightarrow> abs((a::int) div 2) < abs a"
-by arith
+ by arith
-lemma lapprox_rat:
- shows "real (lapprox_rat prec x y) \<le> real x / real y"
+lemma lapprox_rat: "real (lapprox_rat prec x y) \<le> real x / real y"
using round_down by (simp add: lapprox_rat_def)
-lemma mult_div_le: fixes a b:: int assumes "b > 0" shows "a \<ge> b * (a div b)"
+lemma mult_div_le:
+ fixes a b :: int
+ assumes "b > 0"
+ shows "a \<ge> b * (a div b)"
proof -
- from zmod_zdiv_equality'[of a b]
- have "a = b * (a div b) + a mod b" by simp
- also have "... \<ge> b * (a div b) + 0" apply (rule add_left_mono) apply (rule pos_mod_sign)
- using assms by simp
- finally show ?thesis by simp
+ from zmod_zdiv_equality'[of a b] have "a = b * (a div b) + a mod b"
+ by simp
+ also have "\<dots> \<ge> b * (a div b) + 0"
+ apply (rule add_left_mono)
+ apply (rule pos_mod_sign)
+ using assms apply simp
+ done
+ finally show ?thesis
+ by simp
qed
lemma lapprox_rat_nonneg:
@@ -1758,12 +1931,10 @@
by transfer (auto intro!: round_up_le1 simp: rat_precision_def)
qed
-lemma rapprox_rat_nonneg_nonpos:
- "0 \<le> x \<Longrightarrow> y \<le> 0 \<Longrightarrow> real (rapprox_rat n x y) \<le> 0"
+lemma rapprox_rat_nonneg_nonpos: "0 \<le> x \<Longrightarrow> y \<le> 0 \<Longrightarrow> real (rapprox_rat n x y) \<le> 0"
by transfer (simp add: round_up_le0 divide_nonneg_nonpos)
-lemma rapprox_rat_nonpos_nonneg:
- "x \<le> 0 \<Longrightarrow> 0 \<le> y \<Longrightarrow> real (rapprox_rat n x y) \<le> 0"
+lemma rapprox_rat_nonpos_nonneg: "x \<le> 0 \<Longrightarrow> 0 \<le> y \<Longrightarrow> real (rapprox_rat n x y) \<le> 0"
by transfer (simp add: round_up_le0 divide_nonpos_nonneg)
lemma real_divl: "real_divl prec x y \<le> x / y"
@@ -1793,17 +1964,32 @@
by (simp add: bitlen_def)
lemma mantissa_eq_zero_iff: "mantissa x = 0 \<longleftrightarrow> x = 0"
+ (is "?lhs \<longleftrightarrow> ?rhs")
proof
- assume "mantissa x = 0" hence z: "0 = real x" using mantissa_exponent by simp
- show "x = 0" by (simp add: zero_float_def z)
-qed (simp add: zero_float_def)
+ show ?rhs if ?lhs
+ proof -
+ from that have z: "0 = real x"
+ using mantissa_exponent by simp
+ show ?thesis
+ by (simp add: zero_float_def z)
+ qed
+ show ?lhs if ?rhs
+ using that by (simp add: zero_float_def)
+qed
lemma float_upper_bound: "x \<le> 2 powr (bitlen \<bar>mantissa x\<bar> + exponent x)"
-proof (cases "x = 0", simp)
- assume "x \<noteq> 0" hence "mantissa x \<noteq> 0" using mantissa_eq_zero_iff by auto
- have "x = mantissa x * 2 powr (exponent x)" by (rule mantissa_exponent)
- also have "mantissa x \<le> \<bar>mantissa x\<bar>" by simp
- also have "... \<le> 2 powr (bitlen \<bar>mantissa x\<bar>)"
+proof (cases "x = 0")
+ case True
+ then show ?thesis by simp
+next
+ case False
+ then have "mantissa x \<noteq> 0"
+ using mantissa_eq_zero_iff by auto
+ have "x = mantissa x * 2 powr (exponent x)"
+ by (rule mantissa_exponent)
+ also have "mantissa x \<le> \<bar>mantissa x\<bar>"
+ by simp
+ also have "\<dots> \<le> 2 powr (bitlen \<bar>mantissa x\<bar>)"
using bitlen_bounds[of "\<bar>mantissa x\<bar>"] bitlen_nonneg \<open>mantissa x \<noteq> 0\<close>
by (auto simp del: real_of_int_abs simp add: powr_int)
finally show ?thesis by (simp add: powr_add)
@@ -1813,22 +1999,28 @@
assumes "0 < x" "x \<le> 1" "prec \<ge> 1"
shows "1 \<le> real_divl prec 1 x"
proof -
- have "log 2 x \<le> real prec + real \<lfloor>log 2 x\<rfloor>" using \<open>prec \<ge> 1\<close> by arith
+ have "log 2 x \<le> real prec + real \<lfloor>log 2 x\<rfloor>"
+ using \<open>prec \<ge> 1\<close> by arith
from this assms show ?thesis
by (simp add: real_divl_def log_divide round_down_ge1)
qed
lemma float_divl_pos_less1_bound:
"0 < real x \<Longrightarrow> real x \<le> 1 \<Longrightarrow> prec \<ge> 1 \<Longrightarrow> 1 \<le> real (float_divl prec 1 x)"
- by (transfer, rule real_divl_pos_less1_bound)
+ by transfer (rule real_divl_pos_less1_bound)
lemma float_divr: "real x / real y \<le> real (float_divr prec x y)"
by transfer (rule real_divr)
-lemma real_divr_pos_less1_lower_bound: assumes "0 < x" and "x \<le> 1" shows "1 \<le> real_divr prec 1 x"
+lemma real_divr_pos_less1_lower_bound:
+ assumes "0 < x"
+ and "x \<le> 1"
+ shows "1 \<le> real_divr prec 1 x"
proof -
- have "1 \<le> 1 / x" using \<open>0 < x\<close> and \<open>x <= 1\<close> by auto
- also have "\<dots> \<le> real_divr prec 1 x" using real_divr[where x=1 and y=x] by auto
+ have "1 \<le> 1 / x"
+ using \<open>0 < x\<close> and \<open>x <= 1\<close> by auto
+ also have "\<dots> \<le> real_divr prec 1 x"
+ using real_divr[where x=1 and y=x] by auto
finally show ?thesis by auto
qed
@@ -1855,19 +2047,21 @@
assumes "0 \<le> x" "x \<le> y"
shows "truncate_up prec x \<le> truncate_up prec y"
proof -
- {
- assume "\<lfloor>log 2 x\<rfloor> = \<lfloor>log 2 y\<rfloor>"
- hence ?thesis
+ consider "\<lfloor>log 2 x\<rfloor> = \<lfloor>log 2 y\<rfloor>" | "\<lfloor>log 2 x\<rfloor> \<noteq> \<lfloor>log 2 y\<rfloor>" "0 < x" | "x \<le> 0"
+ by arith
+ then show ?thesis
+ proof cases
+ case 1
+ then show ?thesis
using assms
by (auto simp: truncate_up_def round_up_def intro!: ceiling_mono)
- } moreover {
- assume "0 < x"
- hence "log 2 x \<le> log 2 y" using assms by auto
- moreover
- assume "\<lfloor>log 2 x\<rfloor> \<noteq> \<lfloor>log 2 y\<rfloor>"
- ultimately have logless: "log 2 x < log 2 y" and flogless: "\<lfloor>log 2 x\<rfloor> < \<lfloor>log 2 y\<rfloor>"
- unfolding atomize_conj
- by (metis floor_less_cancel linorder_cases not_le)
+ next
+ case 2
+ from assms \<open>0 < x\<close> have "log 2 x \<le> log 2 y"
+ by auto
+ with \<open>\<lfloor>log 2 x\<rfloor> \<noteq> \<lfloor>log 2 y\<rfloor>\<close>
+ have logless: "log 2 x < log 2 y" and flogless: "\<lfloor>log 2 x\<rfloor> < \<lfloor>log 2 y\<rfloor>"
+ by (metis floor_less_cancel linorder_cases not_le)+
have "truncate_up prec x =
real \<lceil>x * 2 powr real (int prec - \<lfloor>log 2 x\<rfloor> - 1)\<rceil> * 2 powr - real (int prec - \<lfloor>log 2 x\<rfloor> - 1)"
using assms by (simp add: truncate_up_def round_up_def)
@@ -1876,10 +2070,10 @@
have "x * 2 powr real (int prec - \<lfloor>log 2 x\<rfloor> - 1) \<le> x * (2 powr real prec / (2 powr log 2 x))"
using real_of_int_floor_add_one_ge[of "log 2 x"] assms
by (auto simp add: algebra_simps powr_divide2 intro!: mult_left_mono)
- thus "x * 2 powr real (int prec - \<lfloor>log 2 x\<rfloor> - 1) \<le> real ((2::int) ^ prec)"
+ then show "x * 2 powr real (int prec - \<lfloor>log 2 x\<rfloor> - 1) \<le> real ((2::int) ^ prec)"
using \<open>0 < x\<close> by (simp add: powr_realpow)
qed
- hence "real \<lceil>x * 2 powr real (int prec - \<lfloor>log 2 x\<rfloor> - 1)\<rceil> \<le> 2 powr int prec"
+ then have "real \<lceil>x * 2 powr real (int prec - \<lfloor>log 2 x\<rfloor> - 1)\<rceil> \<le> 2 powr int prec"
by (auto simp: powr_realpow)
also
have "2 powr - real (int prec - \<lfloor>log 2 x\<rfloor> - 1) \<le> 2 powr - real (int prec - \<lfloor>log 2 y\<rfloor>)"
@@ -1896,14 +2090,13 @@
by (simp add: powr_add)
also have "\<dots> \<le> truncate_up prec y"
by (rule truncate_up)
- finally have ?thesis .
- } moreover {
- assume "~ 0 < x"
- hence ?thesis
+ finally show ?thesis .
+ next
+ case 3
+ then show ?thesis
using assms
by (auto intro!: truncate_up_le)
- } ultimately show ?thesis
- by blast
+ qed
qed
lemma truncate_up_switch_sign_mono:
@@ -1931,20 +2124,22 @@
finally have "\<lfloor>x * 2 powr (- real \<lfloor>log 2 x\<rfloor> - 1)\<rfloor> < 1"
unfolding less_ceiling_eq real_of_int_minus real_of_one
by simp
- moreover
- have "0 \<le> \<lfloor>x * 2 powr (- real \<lfloor>log 2 x\<rfloor> - 1)\<rfloor>"
+ moreover have "0 \<le> \<lfloor>x * 2 powr (- real \<lfloor>log 2 x\<rfloor> - 1)\<rfloor>"
using \<open>x > 0\<close> by auto
ultimately have "\<lfloor>x * 2 powr (- real \<lfloor>log 2 x\<rfloor> - 1)\<rfloor> \<in> {0 ..< 1}"
by simp
- also have "\<dots> \<subseteq> {0}" by auto
- finally have "\<lfloor>x * 2 powr (- real \<lfloor>log 2 x\<rfloor> - 1)\<rfloor> = 0" by simp
+ also have "\<dots> \<subseteq> {0}"
+ by auto
+ finally have "\<lfloor>x * 2 powr (- real \<lfloor>log 2 x\<rfloor> - 1)\<rfloor> = 0"
+ by simp
with assms show ?thesis
by (auto simp: truncate_down_def round_down_def)
qed
lemma truncate_down_switch_sign_mono:
- assumes "x \<le> 0" "0 \<le> y"
- assumes "x \<le> y"
+ assumes "x \<le> 0"
+ and "0 \<le> y"
+ and "x \<le> y"
shows "truncate_down prec x \<le> truncate_down prec y"
proof -
note truncate_down_le[OF \<open>x \<le> 0\<close>]
@@ -1956,32 +2151,36 @@
assumes "0 \<le> x" "x \<le> y"
shows "truncate_down prec x \<le> truncate_down prec y"
proof -
- {
- assume "0 < x" "prec = 0"
- with assms have ?thesis
+ consider "0 < x" "prec = 0" | "x \<le> 0" | "\<lfloor>log 2 \<bar>x\<bar>\<rfloor> = \<lfloor>log 2 \<bar>y\<bar>\<rfloor>" |
+ "0 < x" "\<lfloor>log 2 \<bar>x\<bar>\<rfloor> \<noteq> \<lfloor>log 2 \<bar>y\<bar>\<rfloor>" "prec \<noteq> 0"
+ by arith
+ then show ?thesis
+ proof cases
+ case 1
+ with assms show ?thesis
by (simp add: truncate_down_zeroprec_mono)
- } moreover {
- assume "~ 0 < x"
+ next
+ case 2
with assms have "x = 0" "0 \<le> y" by simp_all
- hence ?thesis
+ then show ?thesis
by (auto intro!: truncate_down_nonneg)
- } moreover {
- assume "\<lfloor>log 2 \<bar>x\<bar>\<rfloor> = \<lfloor>log 2 \<bar>y\<bar>\<rfloor>"
- hence ?thesis
+ next
+ case 3
+ then show ?thesis
using assms
by (auto simp: truncate_down_def round_down_def intro!: floor_mono)
- } moreover {
- assume "0 < x"
- hence "log 2 x \<le> log 2 y" "0 < y" "0 \<le> y" using assms by auto
- moreover
- assume "\<lfloor>log 2 \<bar>x\<bar>\<rfloor> \<noteq> \<lfloor>log 2 \<bar>y\<bar>\<rfloor>"
- ultimately have logless: "log 2 x < log 2 y" and flogless: "\<lfloor>log 2 x\<rfloor> < \<lfloor>log 2 y\<rfloor>"
+ next
+ case 4
+ from \<open>0 < x\<close> have "log 2 x \<le> log 2 y" "0 < y" "0 \<le> y"
+ using assms by auto
+ with \<open>\<lfloor>log 2 \<bar>x\<bar>\<rfloor> \<noteq> \<lfloor>log 2 \<bar>y\<bar>\<rfloor>\<close>
+ have logless: "log 2 x < log 2 y" and flogless: "\<lfloor>log 2 x\<rfloor> < \<lfloor>log 2 y\<rfloor>"
unfolding atomize_conj abs_of_pos[OF \<open>0 < x\<close>] abs_of_pos[OF \<open>0 < y\<close>]
by (metis floor_less_cancel linorder_cases not_le)
- assume "prec \<noteq> 0" hence [simp]: "prec \<ge> Suc 0" by auto
+ from \<open>prec \<noteq> 0\<close> have [simp]: "prec \<ge> Suc 0"
+ by auto
have "2 powr (prec - 1) \<le> y * 2 powr real (prec - 1) / (2 powr log 2 y)"
- using \<open>0 < y\<close>
- by simp
+ using \<open>0 < y\<close> by simp
also have "\<dots> \<le> y * 2 powr real prec / (2 powr (real \<lfloor>log 2 y\<rfloor> + 1))"
using \<open>0 \<le> y\<close> \<open>0 \<le> x\<close> assms(2)
by (auto intro!: powr_mono divide_left_mono
@@ -1992,7 +2191,7 @@
finally have "(2 ^ (prec - 1)) \<le> \<lfloor>y * 2 powr real (int prec - \<lfloor>log 2 \<bar>y\<bar>\<rfloor> - 1)\<rfloor>"
using \<open>0 \<le> y\<close>
by (auto simp: powr_divide2[symmetric] le_floor_eq powr_realpow)
- hence "(2 ^ (prec - 1)) * 2 powr - real (int prec - \<lfloor>log 2 \<bar>y\<bar>\<rfloor> - 1) \<le> truncate_down prec y"
+ then have "(2 ^ (prec - 1)) * 2 powr - real (int prec - \<lfloor>log 2 \<bar>y\<bar>\<rfloor> - 1) \<le> truncate_down prec y"
by (auto simp: truncate_down_def round_down_def)
moreover
{
@@ -2006,9 +2205,10 @@
by (auto intro!: floor_mono)
finally have "x \<le> (2 ^ (prec - 1)) * 2 powr - real (int prec - \<lfloor>log 2 \<bar>y\<bar>\<rfloor> - 1)"
by (auto simp: powr_realpow[symmetric] powr_divide2[symmetric] assms real_of_nat_diff)
- } ultimately have ?thesis
+ }
+ ultimately show ?thesis
by (metis dual_order.trans truncate_down)
- } ultimately show ?thesis by blast
+ qed
qed
lemma truncate_down_eq_truncate_up: "truncate_down p x = - truncate_up p (-x)"
@@ -2029,49 +2229,62 @@
lemma Float_le_zero_iff: "Float a b \<le> 0 \<longleftrightarrow> a \<le> 0"
by (auto simp: zero_float_def mult_le_0_iff) (simp add: not_less [symmetric])
-lemma real_of_float_pprt[simp]: fixes a::float shows "real (pprt a) = pprt (real a)"
+lemma real_of_float_pprt[simp]:
+ fixes a :: float
+ shows "real (pprt a) = pprt (real a)"
unfolding pprt_def sup_float_def max_def sup_real_def by auto
-lemma real_of_float_nprt[simp]: fixes a::float shows "real (nprt a) = nprt (real a)"
+lemma real_of_float_nprt[simp]:
+ fixes a :: float
+ shows "real (nprt a) = nprt (real a)"
unfolding nprt_def inf_float_def min_def inf_real_def by auto
+context
+begin
+
lift_definition int_floor_fl :: "float \<Rightarrow> int" is floor .
-lemma compute_int_floor_fl[code]:
+qualified lemma compute_int_floor_fl[code]:
"int_floor_fl (Float m e) = (if 0 \<le> e then m * 2 ^ nat e else m div (2 ^ (nat (-e))))"
by transfer (simp add: powr_int int_of_reals floor_divide_eq_div del: real_of_ints)
-hide_fact (open) compute_int_floor_fl
lift_definition floor_fl :: "float \<Rightarrow> float" is "\<lambda>x. real (floor x)" by simp
-lemma compute_floor_fl[code]:
+qualified lemma compute_floor_fl[code]:
"floor_fl (Float m e) = (if 0 \<le> e then Float m e else Float (m div (2 ^ (nat (-e)))) 0)"
by transfer (simp add: powr_int int_of_reals floor_divide_eq_div del: real_of_ints)
-hide_fact (open) compute_floor_fl
+
+end
-lemma floor_fl: "real (floor_fl x) \<le> real x" by transfer simp
+lemma floor_fl: "real (floor_fl x) \<le> real x"
+ by transfer simp
-lemma int_floor_fl: "real (int_floor_fl x) \<le> real x" by transfer simp
+lemma int_floor_fl: "real (int_floor_fl x) \<le> real x"
+ by transfer simp
lemma floor_pos_exp: "exponent (floor_fl x) \<ge> 0"
proof (cases "floor_fl x = float_of 0")
case True
- then show ?thesis by (simp add: floor_fl_def)
+ then show ?thesis
+ by (simp add: floor_fl_def)
next
case False
- have eq: "floor_fl x = Float \<lfloor>real x\<rfloor> 0" by transfer simp
+ have eq: "floor_fl x = Float \<lfloor>real x\<rfloor> 0"
+ by transfer simp
obtain i where "\<lfloor>real x\<rfloor> = mantissa (floor_fl x) * 2 ^ i" "0 = exponent (floor_fl x) - int i"
by (rule denormalize_shift[OF eq[THEN eq_reflection] False])
- then show ?thesis by simp
+ then show ?thesis
+ by simp
qed
lemma compute_mantissa[code]:
- "mantissa (Float m e) = (if m = 0 then 0 else if 2 dvd m then mantissa (normfloat (Float m e)) else m)"
+ "mantissa (Float m e) =
+ (if m = 0 then 0 else if 2 dvd m then mantissa (normfloat (Float m e)) else m)"
by (auto simp: mantissa_float Float.abs_eq)
lemma compute_exponent[code]:
- "exponent (Float m e) = (if m = 0 then 0 else if 2 dvd m then exponent (normfloat (Float m e)) else e)"
+ "exponent (Float m e) =
+ (if m = 0 then 0 else if 2 dvd m then exponent (normfloat (Float m e)) else e)"
by (auto simp: exponent_float Float.abs_eq)
end
-