src/HOL/Word/Bit_Representation.thy

prefer one theory for misc material

(*  Title:      HOL/Word/Bit_Representation.thy
    Author:     Jeremy Dawson, NICTA
*)

section \<open>Integers as implicit bit strings\<close>

theory Bit_Representation
  imports Main
begin

lemma int_mod_lem: "0 < n \<Longrightarrow> 0 \<le> b \<and> b < n \<longleftrightarrow> b mod n = b"
  for b n :: int
  apply safe
    apply (erule (1) mod_pos_pos_trivial)
   apply (erule_tac [!] subst)
   apply auto
  done

lemma int_mod_ge: "a < n \<Longrightarrow> 0 < n \<Longrightarrow> a \<le> a mod n"
  for a n :: int
  by (metis dual_order.trans le_cases mod_pos_pos_trivial pos_mod_conj)

lemma int_mod_ge': "b < 0 \<Longrightarrow> 0 < n \<Longrightarrow> b + n \<le> b mod n"
  for b n :: int
  by (metis add_less_same_cancel2 int_mod_ge mod_add_self2)

lemma int_mod_le': "0 \<le> b - n \<Longrightarrow> b mod n \<le> b - n"
  for b n :: int
  by (metis minus_mod_self2 zmod_le_nonneg_dividend)

lemma emep1: "even n \<Longrightarrow> even d \<Longrightarrow> 0 \<le> d \<Longrightarrow> (n + 1) mod d = (n mod d) + 1"
  for n d :: int
  by (auto simp add: pos_zmod_mult_2 add.commute dvd_def)

lemma m1mod2k: "- 1 mod 2 ^ n = (2 ^ n - 1 :: int)"
  by (rule zmod_minus1) simp


subsection \<open>Constructors and destructors for binary integers\<close>

definition Bit :: "int \<Rightarrow> bool \<Rightarrow> int"  (infixl "BIT" 90)
  where "k BIT b = (if b then 1 else 0) + k + k"

lemma Bit_B0: "k BIT False = k + k"
   by (simp add: Bit_def)

lemma Bit_B1: "k BIT True = k + k + 1"
   by (simp add: Bit_def)

lemma Bit_B0_2t: "k BIT False = 2 * k"
  by (rule trans, rule Bit_B0) simp

lemma Bit_B1_2t: "k BIT True = 2 * k + 1"
  by (rule trans, rule Bit_B1) simp

lemma power_BIT: "2 ^ Suc n - 1 = (2 ^ n - 1) BIT True"
  by (simp add: Bit_B1)

definition bin_last :: "int \<Rightarrow> bool"
  where "bin_last w \<longleftrightarrow> w mod 2 = 1"

lemma bin_last_odd: "bin_last = odd"
  by (rule ext) (simp add: bin_last_def even_iff_mod_2_eq_zero)

definition bin_rest :: "int \<Rightarrow> int"
  where "bin_rest w = w div 2"

lemma bin_rl_simp [simp]: "bin_rest w BIT bin_last w = w"
  unfolding bin_rest_def bin_last_def Bit_def
  by (cases "w mod 2 = 0") (use div_mult_mod_eq [of w 2] in simp_all)

lemma bin_rest_BIT [simp]: "bin_rest (x BIT b) = x"
  unfolding bin_rest_def Bit_def
  by (cases b) simp_all

lemma bin_last_BIT [simp]: "bin_last (x BIT b) = b"
  unfolding bin_last_def Bit_def
  by (cases b) simp_all

lemma BIT_eq_iff [iff]: "u BIT b = v BIT c \<longleftrightarrow> u = v \<and> b = c"
  by (auto simp: Bit_def) arith+

lemma BIT_bin_simps [simp]:
  "numeral k BIT False = numeral (Num.Bit0 k)"
  "numeral k BIT True = numeral (Num.Bit1 k)"
  "(- numeral k) BIT False = - numeral (Num.Bit0 k)"
  "(- numeral k) BIT True = - numeral (Num.BitM k)"
  unfolding numeral.simps numeral_BitM
  by (simp_all add: Bit_def del: arith_simps add_numeral_special diff_numeral_special)

lemma BIT_special_simps [simp]:
  shows "0 BIT False = 0"
    and "0 BIT True = 1"
    and "1 BIT False = 2"
    and "1 BIT True = 3"
    and "(- 1) BIT False = - 2"
    and "(- 1) BIT True = - 1"
  by (simp_all add: Bit_def)

lemma Bit_eq_0_iff: "w BIT b = 0 \<longleftrightarrow> w = 0 \<and> \<not> b"
  by (auto simp: Bit_def) arith

lemma Bit_eq_m1_iff: "w BIT b = -1 \<longleftrightarrow> w = -1 \<and> b"
  by (auto simp: Bit_def) arith

lemma BitM_inc: "Num.BitM (Num.inc w) = Num.Bit1 w"
  by (induct w) simp_all

lemma expand_BIT:
  "numeral (Num.Bit0 w) = numeral w BIT False"
  "numeral (Num.Bit1 w) = numeral w BIT True"
  "- numeral (Num.Bit0 w) = (- numeral w) BIT False"
  "- numeral (Num.Bit1 w) = (- numeral (w + Num.One)) BIT True"
  by (simp_all add: add_One BitM_inc)

lemma bin_last_numeral_simps [simp]:
  "\<not> bin_last 0"
  "bin_last 1"
  "bin_last (- 1)"
  "bin_last Numeral1"
  "\<not> bin_last (numeral (Num.Bit0 w))"
  "bin_last (numeral (Num.Bit1 w))"
  "\<not> bin_last (- numeral (Num.Bit0 w))"
  "bin_last (- numeral (Num.Bit1 w))"
  by (simp_all add: bin_last_def zmod_zminus1_eq_if) (auto simp add: divmod_def)

lemma bin_rest_numeral_simps [simp]:
  "bin_rest 0 = 0"
  "bin_rest 1 = 0"
  "bin_rest (- 1) = - 1"
  "bin_rest Numeral1 = 0"
  "bin_rest (numeral (Num.Bit0 w)) = numeral w"
  "bin_rest (numeral (Num.Bit1 w)) = numeral w"
  "bin_rest (- numeral (Num.Bit0 w)) = - numeral w"
  "bin_rest (- numeral (Num.Bit1 w)) = - numeral (w + Num.One)"
  by (simp_all add: bin_rest_def zdiv_zminus1_eq_if) (auto simp add: divmod_def)

lemma less_Bits: "v BIT b < w BIT c \<longleftrightarrow> v < w \<or> v \<le> w \<and> \<not> b \<and> c"
  by (auto simp: Bit_def)

lemma le_Bits: "v BIT b \<le> w BIT c \<longleftrightarrow> v < w \<or> v \<le> w \<and> (\<not> b \<or> c)"
  by (auto simp: Bit_def)

lemma pred_BIT_simps [simp]:
  "x BIT False - 1 = (x - 1) BIT True"
  "x BIT True - 1 = x BIT False"
  by (simp_all add: Bit_B0_2t Bit_B1_2t)

lemma succ_BIT_simps [simp]:
  "x BIT False + 1 = x BIT True"
  "x BIT True + 1 = (x + 1) BIT False"
  by (simp_all add: Bit_B0_2t Bit_B1_2t)

lemma add_BIT_simps [simp]:
  "x BIT False + y BIT False = (x + y) BIT False"
  "x BIT False + y BIT True = (x + y) BIT True"
  "x BIT True + y BIT False = (x + y) BIT True"
  "x BIT True + y BIT True = (x + y + 1) BIT False"
  by (simp_all add: Bit_B0_2t Bit_B1_2t)

lemma mult_BIT_simps [simp]:
  "x BIT False * y = (x * y) BIT False"
  "x * y BIT False = (x * y) BIT False"
  "x BIT True * y = (x * y) BIT False + y"
  by (simp_all add: Bit_B0_2t Bit_B1_2t algebra_simps)

lemma B_mod_2': "X = 2 \<Longrightarrow> (w BIT True) mod X = 1 \<and> (w BIT False) mod X = 0"
  by (simp add: Bit_B0 Bit_B1)

lemma bin_ex_rl: "\<exists>w b. w BIT b = bin"
  by (metis bin_rl_simp)

lemma bin_exhaust: "(\<And>x b. bin = x BIT b \<Longrightarrow> Q) \<Longrightarrow> Q"
by (metis bin_ex_rl)

primrec bin_nth :: "int \<Rightarrow> nat \<Rightarrow> bool"
  where
    Z: "bin_nth w 0 \<longleftrightarrow> bin_last w"
  | Suc: "bin_nth w (Suc n) \<longleftrightarrow> bin_nth (bin_rest w) n"

lemma bin_nth_eq_mod:
  "bin_nth w n \<longleftrightarrow> odd (w div 2 ^ n)"
  by (induction n arbitrary: w) (simp_all add: bin_last_def bin_rest_def odd_iff_mod_2_eq_one zdiv_zmult2_eq)

lemma bin_abs_lem: "bin = (w BIT b) \<Longrightarrow> bin \<noteq> -1 \<longrightarrow> bin \<noteq> 0 \<longrightarrow> nat \<bar>w\<bar> < nat \<bar>bin\<bar>"
  apply clarsimp
  apply (unfold Bit_def)
  apply (cases b)
   apply (clarsimp, arith)
  apply (clarsimp, arith)
  done

lemma bin_induct:
  assumes PPls: "P 0"
    and PMin: "P (- 1)"
    and PBit: "\<And>bin bit. P bin \<Longrightarrow> P (bin BIT bit)"
  shows "P bin"
  apply (rule_tac P=P and a=bin and f1="nat \<circ> abs" in wf_measure [THEN wf_induct])
  apply (simp add: measure_def inv_image_def)
  apply (case_tac x rule: bin_exhaust)
  apply (frule bin_abs_lem)
  apply (auto simp add : PPls PMin PBit)
  done

lemma Bit_div2 [simp]: "(w BIT b) div 2 = w"
  unfolding bin_rest_def [symmetric] by (rule bin_rest_BIT)

lemma bin_nth_eq_iff: "bin_nth x = bin_nth y \<longleftrightarrow> x = y"
proof -
  have bin_nth_lem [rule_format]: "\<forall>y. bin_nth x = bin_nth y \<longrightarrow> x = y"
    apply (induct x rule: bin_induct)
      apply safe
      apply (erule rev_mp)
      apply (induct_tac y rule: bin_induct)
        apply safe
        apply (drule_tac x=0 in fun_cong, force)
       apply (erule notE, rule ext, drule_tac x="Suc x" in fun_cong, force)
      apply (drule_tac x=0 in fun_cong, force)
     apply (erule rev_mp)
     apply (induct_tac y rule: bin_induct)
       apply safe
       apply (drule_tac x=0 in fun_cong, force)
      apply (erule notE, rule ext, drule_tac x="Suc x" in fun_cong, force)
     apply (metis Bit_eq_m1_iff Z bin_last_BIT)
    apply (case_tac y rule: bin_exhaust)
    apply clarify
    apply (erule allE)
    apply (erule impE)
     prefer 2
     apply (erule conjI)
     apply (drule_tac x=0 in fun_cong, force)
    apply (rule ext)
    apply (drule_tac x="Suc x" for x in fun_cong, force)
    done
  show ?thesis
    by (auto elim: bin_nth_lem)
qed

lemmas bin_eqI = ext [THEN bin_nth_eq_iff [THEN iffD1]]

lemma bin_eq_iff: "x = y \<longleftrightarrow> (\<forall>n. bin_nth x n = bin_nth y n)"
  using bin_nth_eq_iff by auto

lemma bin_nth_zero [simp]: "\<not> bin_nth 0 n"
  by (induct n) auto

lemma bin_nth_1 [simp]: "bin_nth 1 n \<longleftrightarrow> n = 0"
  by (cases n) simp_all

lemma bin_nth_minus1 [simp]: "bin_nth (- 1) n"
  by (induct n) auto

lemma bin_nth_0_BIT: "bin_nth (w BIT b) 0 \<longleftrightarrow> b"
  by auto

lemma bin_nth_Suc_BIT: "bin_nth (w BIT b) (Suc n) = bin_nth w n"
  by auto

lemma bin_nth_minus [simp]: "0 < n \<Longrightarrow> bin_nth (w BIT b) n = bin_nth w (n - 1)"
  by (cases n) auto

lemma bin_nth_numeral: "bin_rest x = y \<Longrightarrow> bin_nth x (numeral n) = bin_nth y (pred_numeral n)"
  by (simp add: numeral_eq_Suc)

lemmas bin_nth_numeral_simps [simp] =
  bin_nth_numeral [OF bin_rest_numeral_simps(2)]
  bin_nth_numeral [OF bin_rest_numeral_simps(5)]
  bin_nth_numeral [OF bin_rest_numeral_simps(6)]
  bin_nth_numeral [OF bin_rest_numeral_simps(7)]
  bin_nth_numeral [OF bin_rest_numeral_simps(8)]

lemmas bin_nth_simps =
  bin_nth.Z bin_nth.Suc bin_nth_zero bin_nth_minus1
  bin_nth_numeral_simps

lemma nth_2p_bin: "bin_nth (2 ^ n) m = (m = n)" \<comment> \<open>for use when simplifying with \<open>bin_nth_Bit\<close>\<close>
  apply (induct n arbitrary: m)
   apply clarsimp
   apply safe
   apply (case_tac m)
    apply (auto simp: Bit_B0_2t [symmetric])
  done 


subsection \<open>Truncating binary integers\<close>

definition bin_sign :: "int \<Rightarrow> int"
  where "bin_sign k = (if k \<ge> 0 then 0 else - 1)"

lemma bin_sign_simps [simp]:
  "bin_sign 0 = 0"
  "bin_sign 1 = 0"
  "bin_sign (- 1) = - 1"
  "bin_sign (numeral k) = 0"
  "bin_sign (- numeral k) = -1"
  "bin_sign (w BIT b) = bin_sign w"
  by (simp_all add: bin_sign_def Bit_def)

lemma bin_sign_rest [simp]: "bin_sign (bin_rest w) = bin_sign w"
  by (cases w rule: bin_exhaust) auto

primrec bintrunc :: "nat \<Rightarrow> int \<Rightarrow> int"
  where
    Z : "bintrunc 0 bin = 0"
  | Suc : "bintrunc (Suc n) bin = bintrunc n (bin_rest bin) BIT (bin_last bin)"

primrec sbintrunc :: "nat \<Rightarrow> int \<Rightarrow> int"
  where
    Z : "sbintrunc 0 bin = (if bin_last bin then -1 else 0)"
  | Suc : "sbintrunc (Suc n) bin = sbintrunc n (bin_rest bin) BIT (bin_last bin)"

lemma bintrunc_mod2p: "bintrunc n w = w mod 2 ^ n"
  by (induct n arbitrary: w) (auto simp add: bin_last_def bin_rest_def Bit_def zmod_zmult2_eq)

lemma sbintrunc_mod2p: "sbintrunc n w = (w + 2 ^ n) mod 2 ^ Suc n - 2 ^ n"
proof (induction n arbitrary: w)
  case 0
  then show ?case
    by (auto simp add: bin_last_odd odd_iff_mod_2_eq_one)
next
  case (Suc n)
  moreover have "((bin_rest w + 2 ^ n) mod (2 * 2 ^ n) - 2 ^ n) BIT bin_last w =
    (w + 2 * 2 ^ n) mod (4 * 2 ^ n) - 2 * 2 ^ n"
  proof (cases w rule: parity_cases)
    case even
    then show ?thesis
      by (simp add: bin_last_odd bin_rest_def Bit_B0_2t mult_mod_right)
  next
    case odd
    then have "2 * (w div 2) = w - 1"
      using minus_mod_eq_mult_div [of w 2] by simp
    moreover have "(2 * 2 ^ n + w - 1) mod (2 * 2 * 2 ^ n) + 1 = (2 * 2 ^ n + w) mod (2 * 2 * 2 ^ n)"
      using odd emep1 [of "2 * 2 ^ n + w - 1" "2 * 2 * 2 ^ n"] by simp
    ultimately show ?thesis 
      using odd by (simp add: bin_last_odd bin_rest_def Bit_B1_2t mult_mod_right) (simp add: algebra_simps)
  qed
  ultimately show ?case
    by simp
qed


subsection "Simplifications for (s)bintrunc"

lemma sign_bintr: "bin_sign (bintrunc n w) = 0"
  by (simp add: bintrunc_mod2p bin_sign_def)

lemma bintrunc_n_0 [simp]: "bintrunc n 0 = 0"
  by (simp add: bintrunc_mod2p)

lemma sbintrunc_n_0 [simp]: "sbintrunc n 0 = 0"
  by (simp add: sbintrunc_mod2p)

lemma sbintrunc_n_minus1 [simp]: "sbintrunc n (- 1) = -1"
  by (induct n) auto

lemma bintrunc_Suc_numeral:
  "bintrunc (Suc n) 1 = 1"
  "bintrunc (Suc n) (- 1) = bintrunc n (- 1) BIT True"
  "bintrunc (Suc n) (numeral (Num.Bit0 w)) = bintrunc n (numeral w) BIT False"
  "bintrunc (Suc n) (numeral (Num.Bit1 w)) = bintrunc n (numeral w) BIT True"
  "bintrunc (Suc n) (- numeral (Num.Bit0 w)) = bintrunc n (- numeral w) BIT False"
  "bintrunc (Suc n) (- numeral (Num.Bit1 w)) = bintrunc n (- numeral (w + Num.One)) BIT True"
  by simp_all

lemma sbintrunc_0_numeral [simp]:
  "sbintrunc 0 1 = -1"
  "sbintrunc 0 (numeral (Num.Bit0 w)) = 0"
  "sbintrunc 0 (numeral (Num.Bit1 w)) = -1"
  "sbintrunc 0 (- numeral (Num.Bit0 w)) = 0"
  "sbintrunc 0 (- numeral (Num.Bit1 w)) = -1"
  by simp_all

lemma sbintrunc_Suc_numeral:
  "sbintrunc (Suc n) 1 = 1"
  "sbintrunc (Suc n) (numeral (Num.Bit0 w)) = sbintrunc n (numeral w) BIT False"
  "sbintrunc (Suc n) (numeral (Num.Bit1 w)) = sbintrunc n (numeral w) BIT True"
  "sbintrunc (Suc n) (- numeral (Num.Bit0 w)) = sbintrunc n (- numeral w) BIT False"
  "sbintrunc (Suc n) (- numeral (Num.Bit1 w)) = sbintrunc n (- numeral (w + Num.One)) BIT True"
  by simp_all

lemma bin_sign_lem: "(bin_sign (sbintrunc n bin) = -1) = bin_nth bin n"
  apply (induct n arbitrary: bin)
  apply (case_tac bin rule: bin_exhaust, case_tac b, auto)
  done

lemma nth_bintr: "bin_nth (bintrunc m w) n \<longleftrightarrow> n < m \<and> bin_nth w n"
  apply (induct n arbitrary: w m)
   apply (case_tac m, auto)[1]
  apply (case_tac m, auto)[1]
  done

lemma nth_sbintr: "bin_nth (sbintrunc m w) n = (if n < m then bin_nth w n else bin_nth w m)"
  apply (induct n arbitrary: w m)
   apply (case_tac m)
    apply simp_all
  apply (case_tac m)
   apply simp_all
  done

lemma bin_nth_Bit: "bin_nth (w BIT b) n \<longleftrightarrow> n = 0 \<and> b \<or> (\<exists>m. n = Suc m \<and> bin_nth w m)"
  by (cases n) auto

lemma bin_nth_Bit0:
  "bin_nth (numeral (Num.Bit0 w)) n \<longleftrightarrow>
    (\<exists>m. n = Suc m \<and> bin_nth (numeral w) m)"
  using bin_nth_Bit [where w="numeral w" and b="False"] by simp

lemma bin_nth_Bit1:
  "bin_nth (numeral (Num.Bit1 w)) n \<longleftrightarrow>
    n = 0 \<or> (\<exists>m. n = Suc m \<and> bin_nth (numeral w) m)"
  using bin_nth_Bit [where w="numeral w" and b="True"] by simp

lemma bintrunc_bintrunc_l: "n \<le> m \<Longrightarrow> bintrunc m (bintrunc n w) = bintrunc n w"
  by (rule bin_eqI) (auto simp: nth_bintr)

lemma sbintrunc_sbintrunc_l: "n \<le> m \<Longrightarrow> sbintrunc m (sbintrunc n w) = sbintrunc n w"
  by (rule bin_eqI) (auto simp: nth_sbintr)

lemma bintrunc_bintrunc_ge: "n \<le> m \<Longrightarrow> bintrunc n (bintrunc m w) = bintrunc n w"
  by (rule bin_eqI) (auto simp: nth_bintr)

lemma bintrunc_bintrunc_min [simp]: "bintrunc m (bintrunc n w) = bintrunc (min m n) w"
  by (rule bin_eqI) (auto simp: nth_bintr)

lemma sbintrunc_sbintrunc_min [simp]: "sbintrunc m (sbintrunc n w) = sbintrunc (min m n) w"
  by (rule bin_eqI) (auto simp: nth_sbintr min.absorb1 min.absorb2)

lemmas bintrunc_Pls =
  bintrunc.Suc [where bin="0", simplified bin_last_numeral_simps bin_rest_numeral_simps]

lemmas bintrunc_Min [simp] =
  bintrunc.Suc [where bin="-1", simplified bin_last_numeral_simps bin_rest_numeral_simps]

lemmas bintrunc_BIT  [simp] =
  bintrunc.Suc [where bin="w BIT b", simplified bin_last_BIT bin_rest_BIT] for w b

lemmas bintrunc_Sucs = bintrunc_Pls bintrunc_Min bintrunc_BIT
  bintrunc_Suc_numeral

lemmas sbintrunc_Suc_Pls =
  sbintrunc.Suc [where bin="0", simplified bin_last_numeral_simps bin_rest_numeral_simps]

lemmas sbintrunc_Suc_Min =
  sbintrunc.Suc [where bin="-1", simplified bin_last_numeral_simps bin_rest_numeral_simps]

lemmas sbintrunc_Suc_BIT [simp] =
  sbintrunc.Suc [where bin="w BIT b", simplified bin_last_BIT bin_rest_BIT] for w b

lemmas sbintrunc_Sucs = sbintrunc_Suc_Pls sbintrunc_Suc_Min sbintrunc_Suc_BIT
  sbintrunc_Suc_numeral

lemmas sbintrunc_Pls =
  sbintrunc.Z [where bin="0", simplified bin_last_numeral_simps bin_rest_numeral_simps]

lemmas sbintrunc_Min =
  sbintrunc.Z [where bin="-1", simplified bin_last_numeral_simps bin_rest_numeral_simps]

lemmas sbintrunc_0_BIT_B0 [simp] =
  sbintrunc.Z [where bin="w BIT False", simplified bin_last_numeral_simps bin_rest_numeral_simps]
  for w

lemmas sbintrunc_0_BIT_B1 [simp] =
  sbintrunc.Z [where bin="w BIT True", simplified bin_last_BIT bin_rest_numeral_simps]
  for w

lemmas sbintrunc_0_simps =
  sbintrunc_Pls sbintrunc_Min sbintrunc_0_BIT_B0 sbintrunc_0_BIT_B1

lemmas bintrunc_simps = bintrunc.Z bintrunc_Sucs
lemmas sbintrunc_simps = sbintrunc_0_simps sbintrunc_Sucs

lemma bintrunc_minus: "0 < n \<Longrightarrow> bintrunc (Suc (n - 1)) w = bintrunc n w"
  by auto

lemma sbintrunc_minus: "0 < n \<Longrightarrow> sbintrunc (Suc (n - 1)) w = sbintrunc n w"
  by auto

lemmas bintrunc_minus_simps =
  bintrunc_Sucs [THEN [2] bintrunc_minus [symmetric, THEN trans]]
lemmas sbintrunc_minus_simps =
  sbintrunc_Sucs [THEN [2] sbintrunc_minus [symmetric, THEN trans]]

lemmas thobini1 = arg_cong [where f = "\<lambda>w. w BIT b"] for b

lemmas bintrunc_BIT_I = trans [OF bintrunc_BIT thobini1]
lemmas bintrunc_Min_I = trans [OF bintrunc_Min thobini1]

lemmas bmsts = bintrunc_minus_simps(1-3) [THEN thobini1 [THEN [2] trans]]
lemmas bintrunc_Pls_minus_I = bmsts(1)
lemmas bintrunc_Min_minus_I = bmsts(2)
lemmas bintrunc_BIT_minus_I = bmsts(3)

lemma bintrunc_Suc_lem: "bintrunc (Suc n) x = y \<Longrightarrow> m = Suc n \<Longrightarrow> bintrunc m x = y"
  by auto

lemmas bintrunc_Suc_Ialts =
  bintrunc_Min_I [THEN bintrunc_Suc_lem]
  bintrunc_BIT_I [THEN bintrunc_Suc_lem]

lemmas sbintrunc_BIT_I = trans [OF sbintrunc_Suc_BIT thobini1]

lemmas sbintrunc_Suc_Is =
  sbintrunc_Sucs(1-3) [THEN thobini1 [THEN [2] trans]]

lemmas sbintrunc_Suc_minus_Is =
  sbintrunc_minus_simps(1-3) [THEN thobini1 [THEN [2] trans]]

lemma sbintrunc_Suc_lem: "sbintrunc (Suc n) x = y \<Longrightarrow> m = Suc n \<Longrightarrow> sbintrunc m x = y"
  by auto

lemmas sbintrunc_Suc_Ialts =
  sbintrunc_Suc_Is [THEN sbintrunc_Suc_lem]

lemma sbintrunc_bintrunc_lt: "m > n \<Longrightarrow> sbintrunc n (bintrunc m w) = sbintrunc n w"
  by (rule bin_eqI) (auto simp: nth_sbintr nth_bintr)

lemma bintrunc_sbintrunc_le: "m \<le> Suc n \<Longrightarrow> bintrunc m (sbintrunc n w) = bintrunc m w"
  apply (rule bin_eqI)
  apply (auto simp: nth_sbintr nth_bintr)
   apply (subgoal_tac "x=n", safe, arith+)[1]
  apply (subgoal_tac "x=n", safe, arith+)[1]
  done

lemmas bintrunc_sbintrunc [simp] = order_refl [THEN bintrunc_sbintrunc_le]
lemmas sbintrunc_bintrunc [simp] = lessI [THEN sbintrunc_bintrunc_lt]
lemmas bintrunc_bintrunc [simp] = order_refl [THEN bintrunc_bintrunc_l]
lemmas sbintrunc_sbintrunc [simp] = order_refl [THEN sbintrunc_sbintrunc_l]

lemma bintrunc_sbintrunc' [simp]: "0 < n \<Longrightarrow> bintrunc n (sbintrunc (n - 1) w) = bintrunc n w"
  by (cases n) (auto simp del: bintrunc.Suc)

lemma sbintrunc_bintrunc' [simp]: "0 < n \<Longrightarrow> sbintrunc (n - 1) (bintrunc n w) = sbintrunc (n - 1) w"
  by (cases n) (auto simp del: bintrunc.Suc)

lemma bin_sbin_eq_iff: "bintrunc (Suc n) x = bintrunc (Suc n) y \<longleftrightarrow> sbintrunc n x = sbintrunc n y"
  apply (rule iffI)
   apply (rule box_equals [OF _ sbintrunc_bintrunc sbintrunc_bintrunc])
   apply simp
  apply (rule box_equals [OF _ bintrunc_sbintrunc bintrunc_sbintrunc])
  apply simp
  done

lemma bin_sbin_eq_iff':
  "0 < n \<Longrightarrow> bintrunc n x = bintrunc n y \<longleftrightarrow> sbintrunc (n - 1) x = sbintrunc (n - 1) y"
  by (cases n) (simp_all add: bin_sbin_eq_iff del: bintrunc.Suc)

lemmas bintrunc_sbintruncS0 [simp] = bintrunc_sbintrunc' [unfolded One_nat_def]
lemmas sbintrunc_bintruncS0 [simp] = sbintrunc_bintrunc' [unfolded One_nat_def]

lemmas bintrunc_bintrunc_l' = le_add1 [THEN bintrunc_bintrunc_l]
lemmas sbintrunc_sbintrunc_l' = le_add1 [THEN sbintrunc_sbintrunc_l]

(* although bintrunc_minus_simps, if added to default simpset,
  tends to get applied where it's not wanted in developing the theories,
  we get a version for when the word length is given literally *)

lemmas nat_non0_gr =
  trans [OF iszero_def [THEN Not_eq_iff [THEN iffD2]] refl]

lemma bintrunc_numeral:
  "bintrunc (numeral k) x = bintrunc (pred_numeral k) (bin_rest x) BIT bin_last x"
  by (simp add: numeral_eq_Suc)

lemma sbintrunc_numeral:
  "sbintrunc (numeral k) x = sbintrunc (pred_numeral k) (bin_rest x) BIT bin_last x"
  by (simp add: numeral_eq_Suc)

lemma bintrunc_numeral_simps [simp]:
  "bintrunc (numeral k) (numeral (Num.Bit0 w)) = bintrunc (pred_numeral k) (numeral w) BIT False"
  "bintrunc (numeral k) (numeral (Num.Bit1 w)) = bintrunc (pred_numeral k) (numeral w) BIT True"
  "bintrunc (numeral k) (- numeral (Num.Bit0 w)) = bintrunc (pred_numeral k) (- numeral w) BIT False"
  "bintrunc (numeral k) (- numeral (Num.Bit1 w)) =
    bintrunc (pred_numeral k) (- numeral (w + Num.One)) BIT True"
  "bintrunc (numeral k) 1 = 1"
  by (simp_all add: bintrunc_numeral)

lemma sbintrunc_numeral_simps [simp]:
  "sbintrunc (numeral k) (numeral (Num.Bit0 w)) = sbintrunc (pred_numeral k) (numeral w) BIT False"
  "sbintrunc (numeral k) (numeral (Num.Bit1 w)) = sbintrunc (pred_numeral k) (numeral w) BIT True"
  "sbintrunc (numeral k) (- numeral (Num.Bit0 w)) =
    sbintrunc (pred_numeral k) (- numeral w) BIT False"
  "sbintrunc (numeral k) (- numeral (Num.Bit1 w)) =
    sbintrunc (pred_numeral k) (- numeral (w + Num.One)) BIT True"
  "sbintrunc (numeral k) 1 = 1"
  by (simp_all add: sbintrunc_numeral)

lemma no_bintr_alt1: "bintrunc n = (\<lambda>w. w mod 2 ^ n :: int)"
  by (rule ext) (rule bintrunc_mod2p)

lemma range_bintrunc: "range (bintrunc n) = {i. 0 \<le> i \<and> i < 2 ^ n}"
  apply (unfold no_bintr_alt1)
  apply (auto simp add: image_iff)
  apply (rule exI)
  apply (rule sym)
  using int_mod_lem [symmetric, of "2 ^ n"]
  apply auto
  done

lemma no_sbintr_alt2: "sbintrunc n = (\<lambda>w. (w + 2 ^ n) mod 2 ^ Suc n - 2 ^ n :: int)"
  by (rule ext) (simp add : sbintrunc_mod2p)

lemma range_sbintrunc: "range (sbintrunc n) = {i. - (2 ^ n) \<le> i \<and> i < 2 ^ n}"
  apply (unfold no_sbintr_alt2)
  apply (auto simp add: image_iff eq_diff_eq)

  apply (rule exI)
  apply (auto intro: int_mod_lem [THEN iffD1, symmetric])
  done

lemma sb_inc_lem: "a + 2^k < 0 \<Longrightarrow> a + 2^k + 2^(Suc k) \<le> (a + 2^k) mod 2^(Suc k)"
  for a :: int
  using int_mod_ge' [where n = "2 ^ (Suc k)" and b = "a + 2 ^ k"]
  by simp

lemma sb_inc_lem': "a < - (2^k) \<Longrightarrow> a + 2^k + 2^(Suc k) \<le> (a + 2^k) mod 2^(Suc k)"
  for a :: int
  by (rule sb_inc_lem) simp

lemma sbintrunc_inc: "x < - (2^n) \<Longrightarrow> x + 2^(Suc n) \<le> sbintrunc n x"
  unfolding no_sbintr_alt2 by (drule sb_inc_lem') simp

lemma sb_dec_lem: "0 \<le> - (2 ^ k) + a \<Longrightarrow> (a + 2 ^ k) mod (2 * 2 ^ k) \<le> - (2 ^ k) + a"
  for a :: int
  using int_mod_le'[where n = "2 ^ (Suc k)" and b = "a + 2 ^ k"] by simp

lemma sb_dec_lem': "2 ^ k \<le> a \<Longrightarrow> (a + 2 ^ k) mod (2 * 2 ^ k) \<le> - (2 ^ k) + a"
  for a :: int
  by (rule sb_dec_lem) simp

lemma sbintrunc_dec: "x \<ge> (2 ^ n) \<Longrightarrow> x - 2 ^ (Suc n) >= sbintrunc n x"
  unfolding no_sbintr_alt2 by (drule sb_dec_lem') simp

lemma bintr_ge0: "0 \<le> bintrunc n w"
  by (simp add: bintrunc_mod2p)

lemma bintr_lt2p: "bintrunc n w < 2 ^ n"
  by (simp add: bintrunc_mod2p)

lemma bintr_Min: "bintrunc n (- 1) = 2 ^ n - 1"
  by (simp add: bintrunc_mod2p m1mod2k)

lemma sbintr_ge: "- (2 ^ n) \<le> sbintrunc n w"
  by (simp add: sbintrunc_mod2p)

lemma sbintr_lt: "sbintrunc n w < 2 ^ n"
  by (simp add: sbintrunc_mod2p)

lemma sign_Pls_ge_0: "bin_sign bin = 0 \<longleftrightarrow> bin \<ge> 0"
  for bin :: int
  by (simp add: bin_sign_def)

lemma sign_Min_lt_0: "bin_sign bin = -1 \<longleftrightarrow> bin < 0"
  for bin :: int
  by (simp add: bin_sign_def)

lemma bin_rest_trunc: "bin_rest (bintrunc n bin) = bintrunc (n - 1) (bin_rest bin)"
  by (induct n arbitrary: bin) auto

lemma bin_rest_power_trunc:
  "(bin_rest ^^ k) (bintrunc n bin) = bintrunc (n - k) ((bin_rest ^^ k) bin)"
  by (induct k) (auto simp: bin_rest_trunc)

lemma bin_rest_trunc_i: "bintrunc n (bin_rest bin) = bin_rest (bintrunc (Suc n) bin)"
  by auto

lemma bin_rest_strunc: "bin_rest (sbintrunc (Suc n) bin) = sbintrunc n (bin_rest bin)"
  by (induct n arbitrary: bin) auto

lemma bintrunc_rest [simp]: "bintrunc n (bin_rest (bintrunc n bin)) = bin_rest (bintrunc n bin)"
  apply (induct n arbitrary: bin)
   apply simp
  apply (case_tac bin rule: bin_exhaust)
  apply (auto simp: bintrunc_bintrunc_l)
  done

lemma sbintrunc_rest [simp]: "sbintrunc n (bin_rest (sbintrunc n bin)) = bin_rest (sbintrunc n bin)"
  apply (induct n arbitrary: bin)
   apply simp
  apply (case_tac bin rule: bin_exhaust)
  apply (auto simp: bintrunc_bintrunc_l split: bool.splits)
  done

lemma bintrunc_rest': "bintrunc n \<circ> bin_rest \<circ> bintrunc n = bin_rest \<circ> bintrunc n"
  by (rule ext) auto

lemma sbintrunc_rest': "sbintrunc n \<circ> bin_rest \<circ> sbintrunc n = bin_rest \<circ> sbintrunc n"
  by (rule ext) auto

lemma rco_lem: "f \<circ> g \<circ> f = g \<circ> f \<Longrightarrow> f \<circ> (g \<circ> f) ^^ n = g ^^ n \<circ> f"
  apply (rule ext)
  apply (induct_tac n)
   apply (simp_all (no_asm))
  apply (drule fun_cong)
  apply (unfold o_def)
  apply (erule trans)
  apply simp
  done

lemmas rco_bintr = bintrunc_rest'
  [THEN rco_lem [THEN fun_cong], unfolded o_def]
lemmas rco_sbintr = sbintrunc_rest'
  [THEN rco_lem [THEN fun_cong], unfolded o_def]


subsection \<open>Splitting and concatenation\<close>

primrec bin_split :: "nat \<Rightarrow> int \<Rightarrow> int \<times> int"
  where
    Z: "bin_split 0 w = (w, 0)"
  | Suc: "bin_split (Suc n) w =
      (let (w1, w2) = bin_split n (bin_rest w)
       in (w1, w2 BIT bin_last w))"

lemma [code]:
  "bin_split (Suc n) w = (let (w1, w2) = bin_split n (bin_rest w) in (w1, w2 BIT bin_last w))"
  "bin_split 0 w = (w, 0)"
  by simp_all

primrec bin_cat :: "int \<Rightarrow> nat \<Rightarrow> int \<Rightarrow> int"
  where
    Z: "bin_cat w 0 v = w"
  | Suc: "bin_cat w (Suc n) v = bin_cat w n (bin_rest v) BIT bin_last v"

lemma bin_sign_cat: "bin_sign (bin_cat x n y) = bin_sign x"
  by (induct n arbitrary: y) auto

lemma bin_cat_Suc_Bit: "bin_cat w (Suc n) (v BIT b) = bin_cat w n v BIT b"
  by auto

lemma bin_cat_assoc: "bin_cat (bin_cat x m y) n z = bin_cat x (m + n) (bin_cat y n z)"
  by (induct n arbitrary: z) auto

lemma bin_cat_assoc_sym: "bin_cat x m (bin_cat y n z) = bin_cat (bin_cat x (m - n) y) (min m n) z"
  apply (induct n arbitrary: z m)
   apply clarsimp
  apply (case_tac m, auto)
  done

definition bin_rcat :: "nat \<Rightarrow> int list \<Rightarrow> int"
  where "bin_rcat n = foldl (\<lambda>u v. bin_cat u n v) 0"

fun bin_rsplit_aux :: "nat \<Rightarrow> nat \<Rightarrow> int \<Rightarrow> int list \<Rightarrow> int list"
  where "bin_rsplit_aux n m c bs =
    (if m = 0 \<or> n = 0 then bs
     else
      let (a, b) = bin_split n c
      in bin_rsplit_aux n (m - n) a (b # bs))"

definition bin_rsplit :: "nat \<Rightarrow> nat \<times> int \<Rightarrow> int list"
  where "bin_rsplit n w = bin_rsplit_aux n (fst w) (snd w) []"

fun bin_rsplitl_aux :: "nat \<Rightarrow> nat \<Rightarrow> int \<Rightarrow> int list \<Rightarrow> int list"
  where "bin_rsplitl_aux n m c bs =
    (if m = 0 \<or> n = 0 then bs
     else
      let (a, b) = bin_split (min m n) c
      in bin_rsplitl_aux n (m - n) a (b # bs))"

definition bin_rsplitl :: "nat \<Rightarrow> nat \<times> int \<Rightarrow> int list"
  where "bin_rsplitl n w = bin_rsplitl_aux n (fst w) (snd w) []"

declare bin_rsplit_aux.simps [simp del]
declare bin_rsplitl_aux.simps [simp del]

lemma bin_nth_cat:
  "bin_nth (bin_cat x k y) n =
    (if n < k then bin_nth y n else bin_nth x (n - k))"
  apply (induct k arbitrary: n y)
   apply clarsimp
  apply (case_tac n, auto)
  done

lemma bin_nth_split:
  "bin_split n c = (a, b) \<Longrightarrow>
    (\<forall>k. bin_nth a k = bin_nth c (n + k)) \<and>
    (\<forall>k. bin_nth b k = (k < n \<and> bin_nth c k))"
  apply (induct n arbitrary: b c)
   apply clarsimp
  apply (clarsimp simp: Let_def split: prod.split_asm)
  apply (case_tac k)
  apply auto
  done

lemma bin_cat_zero [simp]: "bin_cat 0 n w = bintrunc n w"
  by (induct n arbitrary: w) auto

lemma bintr_cat1: "bintrunc (k + n) (bin_cat a n b) = bin_cat (bintrunc k a) n b"
  by (induct n arbitrary: b) auto

lemma bintr_cat: "bintrunc m (bin_cat a n b) =
    bin_cat (bintrunc (m - n) a) n (bintrunc (min m n) b)"
  by (rule bin_eqI) (auto simp: bin_nth_cat nth_bintr)

lemma bintr_cat_same [simp]: "bintrunc n (bin_cat a n b) = bintrunc n b"
  by (auto simp add : bintr_cat)

lemma cat_bintr [simp]: "bin_cat a n (bintrunc n b) = bin_cat a n b"
  by (induct n arbitrary: b) auto

lemma split_bintrunc: "bin_split n c = (a, b) \<Longrightarrow> b = bintrunc n c"
  by (induct n arbitrary: b c) (auto simp: Let_def split: prod.split_asm)

lemma bin_cat_split: "bin_split n w = (u, v) \<Longrightarrow> w = bin_cat u n v"
  by (induct n arbitrary: v w) (auto simp: Let_def split: prod.split_asm)

lemma bin_split_cat: "bin_split n (bin_cat v n w) = (v, bintrunc n w)"
  by (induct n arbitrary: w) auto

lemma bin_split_zero [simp]: "bin_split n 0 = (0, 0)"
  by (induct n) auto

lemma bin_split_minus1 [simp]:
  "bin_split n (- 1) = (- 1, bintrunc n (- 1))"
  by (induct n) auto

lemma bin_split_trunc:
  "bin_split (min m n) c = (a, b) \<Longrightarrow>
    bin_split n (bintrunc m c) = (bintrunc (m - n) a, b)"
  apply (induct n arbitrary: m b c, clarsimp)
  apply (simp add: bin_rest_trunc Let_def split: prod.split_asm)
  apply (case_tac m)
   apply (auto simp: Let_def split: prod.split_asm)
  done

lemma bin_split_trunc1:
  "bin_split n c = (a, b) \<Longrightarrow>
    bin_split n (bintrunc m c) = (bintrunc (m - n) a, bintrunc m b)"
  apply (induct n arbitrary: m b c, clarsimp)
  apply (simp add: bin_rest_trunc Let_def split: prod.split_asm)
  apply (case_tac m)
   apply (auto simp: Let_def split: prod.split_asm)
  done

lemma bin_cat_num: "bin_cat a n b = a * 2 ^ n + bintrunc n b"
  apply (induct n arbitrary: b)
   apply clarsimp
  apply (simp add: Bit_def)
  done

lemma bin_split_num: "bin_split n b = (b div 2 ^ n, b mod 2 ^ n)"
  apply (induct n arbitrary: b)
   apply simp
  apply (simp add: bin_rest_def zdiv_zmult2_eq)
  apply (case_tac b rule: bin_exhaust)
  apply simp
  apply (simp add: Bit_def mod_mult_mult1 pos_zmod_mult_2 add.commute)
  done

end