The methods of the RealFrac class produce garbage when the value lies outside the range of the target type, e.g. Prelude GHC.Float> truncate 1.234e11 :: Int -- 32-bits -1154051584 and, in the case of truncate, different garbage when the rewrite rule fires: Prelude GHC.Float> double2Int 1.234e11 -2147483648 I'm currently working on faster implementations of properFraction, truncate, round, ceiling and floor for Float and Double, so I'd like to know - does it matter at all what garbage is returned in the above case? - if it does, what is the desired behaviour (at least for Int, I can't cater for all possibilities)? On a related note, in my benchmarks, truncFloatGen :: Integral a => Float -> a truncFloatGen = fromInteger . truncFloatInteger truncFloatInteger :: Float -> Integer truncFloatInteger x = case decodeFloat x of (m,e) | e == 0 -> m | e < 0 -> let s = -e in if m < 0 then - ((-m) `shiftR` s) else m `shiftR` s | otherwise -> m `shiftL` e is more than twice as fast as GHC.Float.float2Int, the corresponding for Double almost twice as fast as double2Int. Can anybody confirm that the above is faster than float2Int on other machines/architectures? Cheers, Daniel