On 11/04/13 10:24, Simon Peyton-Jones wrote:
Sounds good to me.
It would be fantastic if someone could investigate Levent’s suggestion “Of course, implementations can take advantage of the underlying CPU's native floating-point abs/sign functions if available as well, avoiding explicit tests at the Haskell code; based on the underlying platform”
Otherwise we’ll just end up adding an extra test and everyone’s code will run a little bit slower.
For IEEE floating point numbers, the sign is stored as a single bit, which can be changed with simple bit twiddling: import Data.Bits import Data.Word import Unsafe.Coerce w2f x = unsafeCoerce (x :: Word32) :: Float f2w x = unsafeCoerce (x :: Float) :: Word32 absFloat = w2f . (`clearBit` 31) . f2w signumFloat = w2f . (.|. 0x3f800000) . (.&. 0x80000000) . f2w w2d x = unsafeCoerce (x :: Word64) :: Double d2w x = unsafeCoerce (x :: Double) :: Word64 absDouble = w2d . (`clearBit` 63) . d2w signumDouble = w2d . (.|. 0x3ff0000000000000) . (.&. 0x8000000000000000) . d2w (Tested on linux x86-64) Twan