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| author | Herbert Valerio Riedel <hvr@gnu.org> | 2015-08-29 12:25:45 +0200 |
|---|---|---|
| committer | Ben Gamari <ben@smart-cactus.org> | 2015-08-29 13:08:18 +0200 |
| commit | c7f0626699998fe16871fd442e4199b48cbefb35 (patch) | |
| tree | f96a583647b14d05b3645a861a10fd75cb4fdc92 /libraries/integer-gmp/src/GHC | |
| parent | cd2dc9e2cf80881e96b98d025c2848edeca11ba4 (diff) | |
| download | haskell-c7f0626699998fe16871fd442e4199b48cbefb35.tar.gz | |
integer-gmp: optimise bitBigNat
This is a somewhat minor optimisation exploiting the static knowledge
of the operands involved allowing to save a few allocations.
Reviewers: austin, rwbarton, goldfire, bgamari
Reviewed By: bgamari
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D1179
Diffstat (limited to 'libraries/integer-gmp/src/GHC')
| -rw-r--r-- | libraries/integer-gmp/src/GHC/Integer/Type.hs | 19 |
1 files changed, 18 insertions, 1 deletions
diff --git a/libraries/integer-gmp/src/GHC/Integer/Type.hs b/libraries/integer-gmp/src/GHC/Integer/Type.hs index a04d9ad895..fd7901a6c9 100644 --- a/libraries/integer-gmp/src/GHC/Integer/Type.hs +++ b/libraries/integer-gmp/src/GHC/Integer/Type.hs @@ -1014,8 +1014,25 @@ timesBigNatWord x@(BN# x#) y# where nx# = sizeofBigNat# x +-- | Specialised version of +-- +-- > bitBigNat = shiftLBigNat (wordToBigNat 1##) +-- +-- avoiding a few redundant allocations bitBigNat :: Int# -> BigNat -bitBigNat i# = shiftLBigNat (wordToBigNat 1##) i# -- FIXME +bitBigNat i# + | isTrue# (i# <# 0#) = zeroBigNat -- or maybe 'nullBigNat'? + | isTrue# (i# ==# 0#) = oneBigNat + | True = runS $ do + mbn@(MBN# mba#) <- newBigNat# (li# +# 1#) + -- FIXME: do we really need to zero-init MBAs returned by 'newByteArray#'? + -- clear all limbs (except for the most-significant limb) + _ <- svoid (setByteArray# mba# 0# (li# `uncheckedIShiftL#` GMP_LIMB_SHIFT#) 0#) + -- set single bit in most-significant limb + _ <- svoid (writeBigNat# mbn li# (uncheckedShiftL# 1## bi#)) + unsafeFreezeBigNat# mbn + where + (# li#, bi# #) = quotRemInt# i# GMP_LIMB_BITS# testBitBigNat :: BigNat -> Int# -> Bool testBitBigNat bn i# |