--- a/src/HOL/Parity.thy Fri May 08 06:26:27 2020 +0000
+++ b/src/HOL/Parity.thy Fri May 08 06:26:28 2020 +0000
@@ -934,6 +934,10 @@
qed
qed
+lemma bit_mod_2_iff [simp]:
+ \<open>bit (a mod 2) n \<longleftrightarrow> n = 0 \<and> odd a\<close>
+ by (cases a rule: parity_cases) (simp_all add: bit_def)
+
lemma bit_mask_iff:
\<open>bit (2 ^ m - 1) n \<longleftrightarrow> 2 ^ n \<noteq> 0 \<and> n < m\<close>
by (simp add: bit_def even_mask_div_iff not_le)
@@ -1204,7 +1208,7 @@
by (simp add: take_bit_eq_mod)
lemma take_bit_Suc:
- \<open>take_bit (Suc n) a = take_bit n (a div 2) * 2 + of_bool (odd a)\<close>
+ \<open>take_bit (Suc n) a = take_bit n (a div 2) * 2 + a mod 2\<close>
proof -
have \<open>take_bit (Suc n) (a div 2 * 2 + of_bool (odd a)) = take_bit n (a div 2) * 2 + of_bool (odd a)\<close>
using even_succ_mod_exp [of \<open>2 * (a div 2)\<close> \<open>Suc n\<close>]
@@ -1215,7 +1219,7 @@
qed
lemma take_bit_rec:
- \<open>take_bit n a = (if n = 0 then 0 else take_bit (n - 1) (a div 2) * 2 + of_bool (odd a))\<close>
+ \<open>take_bit n a = (if n = 0 then 0 else take_bit (n - 1) (a div 2) * 2 + a mod 2)\<close>
by (cases n) (simp_all add: take_bit_Suc)
lemma take_bit_Suc_0 [simp]:
@@ -1442,7 +1446,7 @@
lemma take_bit_Suc_bit1 [simp]:
\<open>take_bit (Suc n) (numeral (Num.Bit1 k)) = take_bit n (numeral k) * 2 + 1\<close>
- by (simp add: take_bit_Suc numeral_Bit1_div_2)
+ by (simp add: take_bit_Suc numeral_Bit1_div_2 mod_2_eq_odd)
lemma take_bit_numeral_bit0 [simp]:
\<open>take_bit (numeral l) (numeral (Num.Bit0 k)) = take_bit (pred_numeral l) (numeral k) * 2\<close>
@@ -1450,7 +1454,7 @@
lemma take_bit_numeral_bit1 [simp]:
\<open>take_bit (numeral l) (numeral (Num.Bit1 k)) = take_bit (pred_numeral l) (numeral k) * 2 + 1\<close>
- by (simp add: take_bit_rec numeral_Bit1_div_2)
+ by (simp add: take_bit_rec numeral_Bit1_div_2 mod_2_eq_odd)
lemma take_bit_of_nat:
"take_bit n (of_nat m) = of_nat (take_bit n m)"