From 3fddca81b57286266fc8206b01746a43080a1d39 Mon Sep 17 00:00:00 2001
From: Joe Hendrix <jhendrix@galois.com>
Date: Sun, 29 Nov 2015 23:10:21 -0800
Subject: [PATCH] feat(library/data/bv): Add preliminary bitvector ops.

---
 library/data/bv.lean | 152 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 152 insertions(+)
 create mode 100644 library/data/bv.lean

diff --git a/library/data/bv.lean b/library/data/bv.lean
new file mode 100644
index 000000000..8109c26b6
--- /dev/null
+++ b/library/data/bv.lean
@@ -0,0 +1,152 @@
+/-
+Copyright (c) 2015 Joe Hendrix. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Author: Joe Hendrix
+
+Basic operations on bitvectors.
+
+This is a work-in-progress, and contains additions to other theories.
+-/
+import data.list
+import data.tuple
+
+namespace bv
+open algebra
+open bool
+open eq.ops
+open list
+open nat
+open prod
+open subtype
+open tuple
+
+definition bv [reducible] (n : ℕ) := tuple bool n
+
+-- Create a zero bitvector
+definition bv_zero (n : ℕ) : bv n := replicate ff
+
+-- Create  a bitvector with the constant one.
+definition bv_one  : Π (n : ℕ), bv n
+  | 0 := replicate ff
+  | (succ n) := (replicate ff : bv n) ++ (tt :: nil)
+
+definition bv_cong {a b : ℕ} : (a = b) → bv a → bv b
+| c (tag x p) := tag x (c ▸ p)
+
+section shift
+
+  -- shift left
+  definition bv_shl {n:ℕ} : bv n → ℕ → bv n
+    | x i :=
+       dite (i ≤ n)
+            (λle,
+             let r := dropn i x ++ replicate ff in
+             let eq := calc (n-i) + i = n : nat.sub_add_cancel le in
+             bv_cong eq r)
+            (λp, bv_zero n)
+
+  -- unsigned shift right
+  definition bv_ushr {n:ℕ} : bv n → ℕ → bv n
+    | x i :=
+      dite (i ≤ n)
+           (λle,
+            let y : bv (n-i) := @firstn _ _ (n - i) (sub_le n i) x in
+            let eq := calc (i+(n-i)) = (n - i) + i : add.comm
+                                ...  = n           : nat.sub_add_cancel le in
+            bv_cong eq (replicate ff ++ y))
+           (λgt, bv_zero n)
+
+  -- signed shift right
+  definition bv_sshr {m:ℕ} : bv (succ m) → ℕ → bv (succ m)
+    | x i :=
+      let n := succ m in
+      dite (i ≤ n)
+           (λle,
+            let z : bv i := replicate (head x) in
+            let y : bv (n-i) := @firstn _ _ (n - i) (sub_le n i) x in
+            let eq := calc (i+(n-i)) = (n-i) + i : add.comm
+                                ...  = n         : nat.sub_add_cancel le in
+            bv_cong eq (z ++ y))
+           (λgt, bv_zero n)
+
+end shift
+
+section bitwise
+  variable { n : ℕ }
+
+  -- | Bitwise and
+  definition bv_and : bv n → bv n → bv n := map₂ band
+
+  -- | Bitwise or
+  definition bv_or : bv n → bv n → bv n := map₂ bor
+
+  -- | Bitwise xor
+  definition bv_xor : bv n → bv n → bv n := map₂ bxor
+
+end bitwise
+
+protected definition xor3 (x:bool) (y:bool) (c:bool) := bxor (bxor x y) c
+protected definition carry (x:bool) (y:bool) (c:bool) :=
+  x && y || x && c || y && c
+
+-- Add with carry (no overflow)
+definition bv_adc {n:ℕ} : bv n → bv n → bool → bv (n+1)
+| x y c :=
+  let f := λx y c, (bv.carry x y c, bv.xor3 x y c) in
+  let z := tuple.mapAccumR₂ f x y c in
+  (pr₁ z) :: (pr₂ z)
+
+definition bv_add {n:ℕ} : bv n → bv n → bv n
+| x y := tail (bv_adc x y ff)
+
+protected definition borrow (x:bool) (y:bool) (b:bool) :=
+  bnot x && y || bnot x && b || y && b
+
+-- Subtract with borrow
+definition bv_sbb {n:ℕ} : bv n → bv n → bool → bool × bv n
+| x y b :=
+  let f := λx y c, (bv.borrow x y c, bv.xor3 x y c) in
+  tuple.mapAccumR₂ f x y b
+
+definition bv_sub {n:ℕ} (x y: bv n) := pr₂ (bv_sbb x y ff)
+
+definition bv_neg {n:ℕ} : bv n → bv n
+| x :=
+  let f := λy c, (y || c, bxor y c) in
+  pr₂ (mapAccumR f x ff)
+
+protected definition mulc {n:ℕ} : list bool → bv n → bv n → bv n
+| []      y r := r
+| (tt::x) y r := mulc x y (bv_add r (bv_shl y (length x)))
+| (ff::x) y r := mulc x y r
+
+definition bv_mul {n:ℕ} : bv n → bv n → bv n
+| (tag x px) y := bv.mulc x y (bv_zero n)
+
+definition bv_has_zero [instance] {n : ℕ} : has_zero (bv n) :=
+  has_zero.mk (bv_zero n)
+definition bv_has_one [instance] {n : ℕ} : has_one (bv n) :=
+  has_one.mk (bv_one n)
+definition bv_has_add [instance] {n : ℕ} : has_add (bv n) :=
+  has_add.mk bv_add
+definition bv_has_sub [instance] {n : ℕ} : has_sub (bv n) :=
+  has_sub.mk bv_sub
+definition bv_has_neg [instance] {n : ℕ} : has_neg (bv n) :=
+  has_neg.mk bv_neg
+definition bv_has_mul [instance] {n : ℕ} : has_mul (bv n) :=
+  has_mul.mk bv_mul
+
+section from_bv
+  variable {A : Type}
+
+  protected definition fold_list_bits [p : has_add A]  [q : has_one A]
+    : list bool → A → A
+  | [] r := r
+  | (tt::l) r := fold_list_bits l (r+r+1)
+  | (ff::l) r := fold_list_bits l (r+r)
+
+  -- Convert a bitvector to another number.
+  definition from_bv [p : has_add A] [q0 : has_zero A] [q1 : has_one A] {w:nat} (v:bv w) : A :=
+    bv.fold_list_bits (to_list v) 0
+end from_bv
+end bv