On Dec 4, 2007 11:51 AM, Don Stewart <[EMAIL PROTECTED]> wrote:
> Awesome. We can use this in Data.Bits, if you've got some QuickChecks
> for it.
Hear hear. But is there any way to just make the compiler use
fastTestBit in place of testBit :: (Bits a) => a -> Int -> Bool when a
= Integer? (That is, without having to introduce a new function to
the public interface of Data.Bits.) Some kind of SPECIALIZE pragma,
perhaps?
I've attached a program with two QuickCheck properties. Unfortunately
they fail on negative Integers. I can't figure out why.
{-# OPTIONS_GHC -fglasgow-exts #-}
module Main where
import Test.QuickCheck
import Data.Bits
import GHC.Exts
fastTestBit :: Integer -> Int -> Bool
fastTestBit n i = case n of
S# m -> testBit (I# m) i
J# l d -> let I# w = shiftR i 6
b = i .&. 63
in testBit (I# (indexIntArray# d w)) b
prop_testBit1 :: Integer -> Int -> Bool
prop_testBit1 i n = testBit i n == fastTestBit i n
-- Test fastTestBit on large Integers
prop_testBit2 :: Integer -> Int -> Int -> Bool
prop_testBit2 i j n = testBit k n == fastTestBit k n where k = i ^ (abs j)
main = do
putStrLn "Testing prop_testBit1:"
quickCheck prop_testBit1
putStrLn "Testing prop_testBit2:"
quickCheck prop_testBit2
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