GaloisInc/cryptol
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Merge pull request #1170 from GaloisInc/faster-pmod

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Add a shortcut to speed up concrete evaluation of pmod.
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brianhuffman 2021-04-28 16:31:21 -07:00 committed by GitHub
commit 282613d320
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src/Cryptol/F2.hs
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@ -32,7 +32,7 @@ pdiv w x m = go (w-1) 0 0
pmod :: Int -> Integer -> Integer -> Integer
pmod w x m = mask .&. go 0 0 (reduce 1)
pmod w x m = go degree (x .&. mask) (clearBit m degree)
where
degree :: Int
degree = fromInteger (widthInteger m - 1)
@ -43,6 +43,7 @@ pmod w x m = mask .&. go 0 0 (reduce 1)
mask = bit degree - 1
-- invariant: z and p are in the range [0..mask]
go !i !z !p
| i < w = go (i+1) (if testBit x i then z `xor` p else z) (reduce (p `shiftL` 1))
| otherwise = z