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| author | Takano Akio <tak@anoak.io> | 2016-09-04 13:22:22 -0400 |
|---|---|---|
| committer | Ben Gamari <ben@smart-cactus.org> | 2016-09-05 14:58:20 -0400 |
| commit | 6ea62427de419ea071e1ea79ad0c15d9f4e90a67 (patch) | |
| tree | 370423005b992268abf3b401d445bb48efed39bf /compiler/utils/Util.hs | |
| parent | 71dd6e4429833238bcdaf96da8e2e41a62dacbf4 (diff) | |
| download | haskell-6ea62427de419ea071e1ea79ad0c15d9f4e90a67.tar.gz | |
Turn divInt# and modInt# into bitwise operations when possible
This implements #5615 for divInt# and modInt#.
I also included rules to do constant-folding when the both arguments
are known.
Test Plan: validate
Reviewers: austin, simonmar, bgamari
Reviewed By: bgamari
Subscribers: hvr, thomie
Differential Revision: https://phabricator.haskell.org/D2486
GHC Trac Issues: #5615
Diffstat (limited to 'compiler/utils/Util.hs')
| -rw-r--r-- | compiler/utils/Util.hs | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/compiler/utils/Util.hs b/compiler/utils/Util.hs index 121fdbbf6f..0b16fba72d 100644 --- a/compiler/utils/Util.hs +++ b/compiler/utils/Util.hs @@ -78,6 +78,9 @@ module Util ( -- * Argument processing getCmd, toCmdArgs, toArgs, + -- * Integers + exactLog2, + -- * Floating point readRational, @@ -985,6 +988,27 @@ toArgs str Right (arg, rest) _ -> Left ("Couldn't read " ++ show s ++ " as String") +----------------------------------------------------------------------------- +-- Integers + +-- This algorithm for determining the $\log_2$ of exact powers of 2 comes +-- from GCC. It requires bit manipulation primitives, and we use GHC +-- extensions. Tough. + +exactLog2 :: Integer -> Maybe Integer +exactLog2 x + = if (x <= 0 || x >= 2147483648) then + Nothing + else + if (x .&. (-x)) /= x then + Nothing + else + Just (pow2 x) + where + pow2 x | x == 1 = 0 + | otherwise = 1 + pow2 (x `shiftR` 1) + + {- -- ----------------------------------------------------------------------------- -- Floats |