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Diffstat (limited to 'src/Util/ZUtil/Definitions.v')
| -rw-r--r-- | src/Util/ZUtil/Definitions.v | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/src/Util/ZUtil/Definitions.v b/src/Util/ZUtil/Definitions.v index fb7754a7a..f6892be13 100644 --- a/src/Util/ZUtil/Definitions.v +++ b/src/Util/ZUtil/Definitions.v @@ -1,6 +1,7 @@ Require Import Coq.ZArith.ZArith. Require Import Crypto.Util.Decidable. Require Import Crypto.Util.ZUtil.Notations. +Require Import Crypto.Util.LetIn. Local Open Scope Z_scope. Module Z. @@ -36,7 +37,15 @@ Module Z. else ((x + y) mod bound, (x + y) / bound). Definition mul_split_at_bitwidth (bitwidth : Z) (x y : Z) : Z * Z - := ((x * y) mod 2^bitwidth, (x * y) / 2^bitwidth). + := dlet xy := x * y in + (match bitwidth with + | Z.pos _ | Z0 => xy &' Z.ones bitwidth + | Z.neg _ => xy mod 2^bitwidth + end, + match bitwidth with + | Z.pos _ | Z0 => xy >> bitwidth + | Z.neg _ => xy / 2^bitwidth + end). Definition mul_split (s x y : Z) : Z * Z := if s =? 2^Z.log2 s then mul_split_at_bitwidth (Z.log2 s) x y |