Theory ComputeFloat

(*  Title:      HOL/Matrix_LP/ComputeFloat.thy
    Author:     Steven Obua
*)

section ‹Floating Point Representation of the Reals›

theory ComputeFloat
imports Complex_Main "HOL-Library.Lattice_Algebras"
begin

ML_file ‹~~/src/Tools/float.ML›

(*FIXME surely floor should be used? This file is full of redundant material.*)

definition int_of_real :: "real ⇒ int"
  where "int_of_real x = (SOME y. real_of_int y = x)"

definition real_is_int :: "real ⇒ bool"
  where "real_is_int x = (∃(u::int). x = real_of_int u)"

lemma real_is_int_def2: "real_is_int x = (x = real_of_int (int_of_real x))"
  by (auto simp add: real_is_int_def int_of_real_def)

lemma real_is_int_real[simp]: "real_is_int (real_of_int (x::int))"
by (auto simp add: real_is_int_def int_of_real_def)

lemma int_of_real_real[simp]: "int_of_real (real_of_int x) = x"
by (simp add: int_of_real_def)

lemma real_int_of_real[simp]: "real_is_int x ⟹ real_of_int (int_of_real x) = x"
by (auto simp add: int_of_real_def real_is_int_def)

lemma real_is_int_add_int_of_real: "real_is_int a ⟹ real_is_int b ⟹ (int_of_real (a+b)) = (int_of_real a) + (int_of_real b)"
by (auto simp add: int_of_real_def real_is_int_def)

lemma real_is_int_add[simp]: "real_is_int a ⟹ real_is_int b ⟹ real_is_int (a+b)"
apply (subst real_is_int_def2)
apply (simp add: real_is_int_add_int_of_real real_int_of_real)
done

lemma int_of_real_sub: "real_is_int a ⟹ real_is_int b ⟹ (int_of_real (a-b)) = (int_of_real a) - (int_of_real b)"
by (auto simp add: int_of_real_def real_is_int_def)

lemma real_is_int_sub[simp]: "real_is_int a ⟹ real_is_int b ⟹ real_is_int (a-b)"
apply (subst real_is_int_def2)
apply (simp add: int_of_real_sub real_int_of_real)
done

lemma real_is_int_rep: "real_is_int x ⟹ ∃!(a::int). real_of_int a = x"
by (auto simp add: real_is_int_def)

lemma int_of_real_mult:
  assumes "real_is_int a" "real_is_int b"
  shows "(int_of_real (a*b)) = (int_of_real a) * (int_of_real b)"
  using assms
  by (auto simp add: real_is_int_def of_int_mult[symmetric]
           simp del: of_int_mult)

lemma real_is_int_mult[simp]: "real_is_int a ⟹ real_is_int b ⟹ real_is_int (a*b)"
apply (subst real_is_int_def2)
apply (simp add: int_of_real_mult)
done

lemma real_is_int_0[simp]: "real_is_int (0::real)"
by (simp add: real_is_int_def int_of_real_def)

lemma real_is_int_1[simp]: "real_is_int (1::real)"
proof -
  have "real_is_int (1::real) = real_is_int(real_of_int (1::int))" by auto
  also have "… = True" by (simp only: real_is_int_real)
  ultimately show ?thesis by auto
qed

lemma real_is_int_n1: "real_is_int (-1::real)"
proof -
  have "real_is_int (-1::real) = real_is_int(real_of_int (-1::int))" by auto
  also have "… = True" by (simp only: real_is_int_real)
  ultimately show ?thesis by auto
qed

lemma real_is_int_numeral[simp]: "real_is_int (numeral x)"
  by (auto simp: real_is_int_def intro!: exI[of _ "numeral x"])

lemma real_is_int_neg_numeral[simp]: "real_is_int (- numeral x)"
  by (auto simp: real_is_int_def intro!: exI[of _ "- numeral x"])

lemma int_of_real_0[simp]: "int_of_real (0::real) = (0::int)"
by (simp add: int_of_real_def)

lemma int_of_real_1[simp]: "int_of_real (1::real) = (1::int)"
proof -
  have 1: "(1::real) = real_of_int (1::int)" by auto
  show ?thesis by (simp only: 1 int_of_real_real)
qed

lemma int_of_real_numeral[simp]: "int_of_real (numeral b) = numeral b"
  unfolding int_of_real_def by simp

lemma int_of_real_neg_numeral[simp]: "int_of_real (- numeral b) = - numeral b"
  unfolding int_of_real_def
  by (metis int_of_real_def int_of_real_real of_int_minus of_int_of_nat_eq of_nat_numeral) 

lemma int_div_zdiv: "int (a div b) = (int a) div (int b)"
by (rule zdiv_int)

lemma int_mod_zmod: "int (a mod b) = (int a) mod (int b)"
by (rule zmod_int)

lemma abs_div_2_less: "a ≠ 0 ⟹ a ≠ -1 ⟹ ¦(a::int) div 2¦ < ¦a¦"
by arith

lemma norm_0_1: "(1::_::numeral) = Numeral1"
  by auto

lemma add_left_zero: "0 + a = (a::'a::comm_monoid_add)"
  by simp

lemma add_right_zero: "a + 0 = (a::'a::comm_monoid_add)"
  by simp

lemma mult_left_one: "1 * a = (a::'a::semiring_1)"
  by simp

lemma mult_right_one: "a * 1 = (a::'a::semiring_1)"
  by simp

lemma int_pow_0: "(a::int)^0 = 1"
  by simp

lemma int_pow_1: "(a::int)^(Numeral1) = a"
  by simp

lemma one_eq_Numeral1_nring: "(1::'a::numeral) = Numeral1"
  by simp

lemma one_eq_Numeral1_nat: "(1::nat) = Numeral1"
  by simp

lemma zpower_Pls: "(z::int)^0 = Numeral1"
  by simp

lemma fst_cong: "a=a' ⟹ fst (a,b) = fst (a',b)"
  by simp

lemma snd_cong: "b=b' ⟹ snd (a,b) = snd (a,b')"
  by simp

lemma lift_bool: "x ⟹ x=True"
  by simp

lemma nlift_bool: "~x ⟹ x=False"
  by simp

lemma not_false_eq_true: "(~ False) = True" by simp

lemma not_true_eq_false: "(~ True) = False" by simp

lemmas powerarith = nat_numeral power_numeral_even
  power_numeral_odd zpower_Pls

definition float :: "(int × int) ⇒ real" where
  "float = (λ(a, b). real_of_int a * 2 powr real_of_int b)"

lemma float_add_l0: "float (0, e) + x = x"
  by (simp add: float_def)

lemma float_add_r0: "x + float (0, e) = x"
  by (simp add: float_def)

lemma float_add:
  "float (a1, e1) + float (a2, e2) =
  (if e1<=e2 then float (a1+a2*2^(nat(e2-e1)), e1) else float (a1*2^(nat (e1-e2))+a2, e2))"
  by (simp add: float_def algebra_simps powr_realpow[symmetric] powr_diff)

lemma float_mult_l0: "float (0, e) * x = float (0, 0)"
  by (simp add: float_def)

lemma float_mult_r0: "x * float (0, e) = float (0, 0)"
  by (simp add: float_def)

lemma float_mult:
  "float (a1, e1) * float (a2, e2) = (float (a1 * a2, e1 + e2))"
  by (simp add: float_def powr_add)

lemma float_minus:
  "- (float (a,b)) = float (-a, b)"
  by (simp add: float_def)

lemma zero_le_float:
  "(0 <= float (a,b)) = (0 <= a)"
  by (simp add: float_def zero_le_mult_iff)

lemma float_le_zero:
  "(float (a,b) <= 0) = (a <= 0)"
  by (simp add: float_def mult_le_0_iff)

lemma float_abs:
  "¦float (a,b)¦ = (if 0 <= a then (float (a,b)) else (float (-a,b)))"
  by (simp add: float_def abs_if mult_less_0_iff not_less)

lemma float_zero:
  "float (0, b) = 0"
  by (simp add: float_def)

lemma float_pprt:
  "pprt (float (a, b)) = (if 0 <= a then (float (a,b)) else (float (0, b)))"
  by (auto simp add: zero_le_float float_le_zero float_zero)

lemma float_nprt:
  "nprt (float (a, b)) = (if 0 <= a then (float (0,b)) else (float (a, b)))"
  by (auto simp add: zero_le_float float_le_zero float_zero)

definition lbound :: "real ⇒ real"
  where "lbound x = min 0 x"

definition ubound :: "real ⇒ real"
  where "ubound x = max 0 x"

lemma lbound: "lbound x ≤ x"   
  by (simp add: lbound_def)

lemma ubound: "x ≤ ubound x"
  by (simp add: ubound_def)

lemma pprt_lbound: "pprt (lbound x) = float (0, 0)"
  by (auto simp: float_def lbound_def)

lemma nprt_ubound: "nprt (ubound x) = float (0, 0)"
  by (auto simp: float_def ubound_def)

lemmas floatarith[simplified norm_0_1] = float_add float_add_l0 float_add_r0 float_mult float_mult_l0 float_mult_r0 
          float_minus float_abs zero_le_float float_pprt float_nprt pprt_lbound nprt_ubound

(* for use with the compute oracle *)
lemmas arith = arith_simps rel_simps diff_nat_numeral nat_0
  nat_neg_numeral powerarith floatarith not_false_eq_true not_true_eq_false

ML_file ‹float_arith.ML›

end