Re: [Haskell-cafe] containers license issue

2012/12/12 Johan Tibell :

On Wed, Dec 12, 2012 at 10:40 AM, Clark Gaebel wrote:

...

I just did a quick derivation from http://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2 to get the highest bit mask, and did not reference FXT nor the containers implementation. Here is my code:

highestBitMask :: Word64 -> Word64 highestBitMask x1 = let x2 = x1 .|. x1 `shiftR` 1 x3 = x2 .|. x2 `shiftR` 2 x4 = x3 .|. x3 `shiftR` 4 x5 = x4 .|. x4 `shiftR` 8 x6 = x5 .|. x5 `shiftR` 16 x7 = x6 .|. x6 `shiftR` 32 in x7 `xor` (x7 `shiftR` 1)

This code is hereby released into the public domain. Problem solved.

I will integrate this into containers later today.

Note that I think the current implementation use a series of case expression instead of a let binding, possibly to force the evaluation.