Donald Bruce Stewart wrote:
john:
so I have this simple bit of code, which should be fast but seems to be being compiled to something very slow.
import Data.Word import Data.Bits
fhb :: Word -> Word fhb w = b1 .|. b2 where b2 = if 0xFFFF0000 .&. w /= 0 then 0x2 else 0 b1 = if 0xFF00FF00 .&. w /= 0 then 0x1 else 0
M.lit = case GHC.Prim.addIntC# 2147418113 2147483647
If I understand the code correctly this happens in the desugaring pass already. The literal 0xFFFF0000 exceeds the range of Int so it's expressed with smaller numbers (see deSugar/DsUtils.lhs, mkIntegerExpr); in this case it becomes fromInteger (0x70000001 + 0x7FFFFFFF), which matches the above line exactly. Btw, the comment in rename/RnTypes about this ("Big integer literals are built [...]") is wrong, as it refers to mkIntegerLit instead of mkIntegerExpr. This suggests that as a workaround, using -0x00010000 and -0x00FF0100 should help (but the code will depend on the word size then). Bertram