Mark Dickinson <[EMAIL PROTECTED]> added the comment:
[Tim]
> if you're concerned about speed, it would probably pay to eliminate all
> library calls except one to frexp().
Indeed it would! Here's a revised patch that avoids use of fmod. Speed is
comparable with the current
version. Here are some timings for summing random values on OS X/Core 2 Duo,
on a non-debug build of the
trunk. lsum is the patched version, msum is the version in the current trunk;
timings are in seconds.
| lsum | msum
------------------------------------------------+----------+---------
50000 random values in [0, 1) | 0.003091 | 0.002540
50000 random values in [0, 1), sorted | 0.003202 | 0.003043
50000 random values in [0, 1), reverse order | 0.003201 | 0.002587
50000 random values in [-1, 1) | 0.003229 | 0.002829
50000 random values in [-1, 1), sorted | 0.003183 | 0.002629
50000 random values in [-1, 1), reverse order | 0.003195 | 0.002731
50000 random exponential values | 0.003994 | 0.006178
50000 random exponential values, sorted | 0.003713 | 0.007933
50000 random exponential values, reverse order | 0.003714 | 0.002849
Note that lsum doesn't suffer from the 'fragmentation of partials' problem that
slows down msum for sorted
datasets.
I'll do some timings on Linux/x86 as well.
Added file: http://bugs.python.org/file11014/fsum10.patch
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<http://bugs.python.org/issue2819>
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