(* Title: HOL/Word/Bit_Comparison.thy Author: Stefan Berghofer Copyright: secunet Security Networks AG Comparison on bit operations on integers. *) theory Bit_Comparison imports Bits_Int begin lemma AND_lower [simp]: fixes x :: int and y :: int assumes "0 ≤ x" shows "0 ≤ x AND y" using assms proof (induct x arbitrary: y rule: bin_induct) case (3 bin bit) show ?case proof (cases y rule: bin_exhaust) case (1 bin' bit') from 3 have "0 ≤ bin" by (cases bit) (simp_all add: Bit_def) then have "0 ≤ bin AND bin'" by (rule 3) with 1 show ?thesis by simp (simp add: Bit_def) qed next case 2 then show ?case by (simp only: Min_def) qed simp lemma OR_lower [simp]: fixes x :: int and y :: int assumes "0 ≤ x" "0 ≤ y" shows "0 ≤ x OR y" using assms proof (induct x arbitrary: y rule: bin_induct) case (3 bin bit) show ?case proof (cases y rule: bin_exhaust) case (1 bin' bit') from 3 have "0 ≤ bin" by (cases bit) (simp_all add: Bit_def) moreover from 1 3 have "0 ≤ bin'" by (cases bit') (simp_all add: Bit_def) ultimately have "0 ≤ bin OR bin'" by (rule 3) with 1 show ?thesis by simp (simp add: Bit_def) qed qed simp_all lemma XOR_lower [simp]: fixes x :: int and y :: int assumes "0 ≤ x" "0 ≤ y" shows "0 ≤ x XOR y" using assms proof (induct x arbitrary: y rule: bin_induct) case (3 bin bit) show ?case proof (cases y rule: bin_exhaust) case (1 bin' bit') from 3 have "0 ≤ bin" by (cases bit) (simp_all add: Bit_def) moreover from 1 3 have "0 ≤ bin'" by (cases bit') (simp_all add: Bit_def) ultimately have "0 ≤ bin XOR bin'" by (rule 3) with 1 show ?thesis by simp (simp add: Bit_def) qed next case 2 then show ?case by (simp only: Min_def) qed simp lemma AND_upper1 [simp]: fixes x :: int and y :: int assumes "0 ≤ x" shows "x AND y ≤ x" using assms proof (induct x arbitrary: y rule: bin_induct) case (3 bin bit) show ?case proof (cases y rule: bin_exhaust) case (1 bin' bit') from 3 have "0 ≤ bin" by (cases bit) (simp_all add: Bit_def) then have "bin AND bin' ≤ bin" by (rule 3) with 1 show ?thesis by simp (simp add: Bit_def) qed next case 2 then show ?case by (simp only: Min_def) qed simp lemmas AND_upper1' [simp] = order_trans [OF AND_upper1] lemmas AND_upper1'' [simp] = order_le_less_trans [OF AND_upper1] lemma AND_upper2 [simp]: fixes x :: int and y :: int assumes "0 ≤ y" shows "x AND y ≤ y" using assms proof (induct y arbitrary: x rule: bin_induct) case (3 bin bit) show ?case proof (cases x rule: bin_exhaust) case (1 bin' bit') from 3 have "0 ≤ bin" by (cases bit) (simp_all add: Bit_def) then have "bin' AND bin ≤ bin" by (rule 3) with 1 show ?thesis by simp (simp add: Bit_def) qed next case 2 then show ?case by (simp only: Min_def) qed simp lemmas AND_upper2' [simp] = order_trans [OF AND_upper2] lemmas AND_upper2'' [simp] = order_le_less_trans [OF AND_upper2] lemma OR_upper: fixes x :: int and y :: int assumes "0 ≤ x" "x < 2 ^ n" "y < 2 ^ n" shows "x OR y < 2 ^ n" using assms proof (induct x arbitrary: y n rule: bin_induct) case (3 bin bit) show ?case proof (cases y rule: bin_exhaust) case (1 bin' bit') show ?thesis proof (cases n) case 0 with 3 have "bin BIT bit = 0" by simp then have "bin = 0" and "¬ bit" by (auto simp add: Bit_def split: if_splits) arith then show ?thesis using 0 1 ‹y < 2 ^ n› by simp next case (Suc m) from 3 have "0 ≤ bin" by (cases bit) (simp_all add: Bit_def) moreover from 3 Suc have "bin < 2 ^ m" by (cases bit) (simp_all add: Bit_def) moreover from 1 3 Suc have "bin' < 2 ^ m" by (cases bit') (simp_all add: Bit_def) ultimately have "bin OR bin' < 2 ^ m" by (rule 3) with 1 Suc show ?thesis by simp (simp add: Bit_def) qed qed qed simp_all lemma XOR_upper: fixes x :: int and y :: int assumes "0 ≤ x" "x < 2 ^ n" "y < 2 ^ n" shows "x XOR y < 2 ^ n" using assms proof (induct x arbitrary: y n rule: bin_induct) case (3 bin bit) show ?case proof (cases y rule: bin_exhaust) case (1 bin' bit') show ?thesis proof (cases n) case 0 with 3 have "bin BIT bit = 0" by simp then have "bin = 0" and "¬ bit" by (auto simp add: Bit_def split: if_splits) arith then show ?thesis using 0 1 ‹y < 2 ^ n› by simp next case (Suc m) from 3 have "0 ≤ bin" by (cases bit) (simp_all add: Bit_def) moreover from 3 Suc have "bin < 2 ^ m" by (cases bit) (simp_all add: Bit_def) moreover from 1 3 Suc have "bin' < 2 ^ m" by (cases bit') (simp_all add: Bit_def) ultimately have "bin XOR bin' < 2 ^ m" by (rule 3) with 1 Suc show ?thesis by simp (simp add: Bit_def) qed qed next case 2 then show ?case by (simp only: Min_def) qed simp end