Re: [Haskell-cafe] fast integer base-2 log function?

Yes, I suspect you are right. I didn't look into that in much detail, although I did try exchanging "(2 ^ 50000000)" with "(1 `shiftL` 50000000)"; but that didn't make any difference. Uwe On Fri, Feb 15, 2008 at 9:21 AM, Ryan Ingram wrote:

On Thu, Feb 14, 2008 at 8:23 PM, Uwe Hollerbach wrote:

...

Stefan's routine is, as expected, much much faster still: I tested the first two routines on numbers with 5 million or so bits and they took ~20 seconds of CPU time, whereas I tested Stefan's routine with numbers with 50 million bits, and it took ~11 seconds of CPU time.

This seems wrong to me; that routine should take a small constant amount of time. I suspect you are measuring the time to construct the 50-million bit numbers as well. If you constructed a single number and called this routine on it several times I am sure you would get far different results, with the first routines taking ~7-11s each and Stefan's GHC/GMP-magic taking almost nothing.

-- ryan