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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 |