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Red Hat Engineer Improves Math Performance of Glibc
jones_supa writes: Siddhesh Poyarekar from Red Hat has taken a professional look into mathematical functions found in Glibc (the GNU C library). He has been able to provide an 8-times performance improvement to slowest path of pow() function. Other transcendentals got similar improvements since the fixes were mostly in the generic multiple precision code. These improvements already went into glibc-2.18 upstream. Siddhesh believes that a lot of the low hanging fruit has now been picked, but that this is definitely not the end of the road for improvements in the multiple precision performance. There are other more complicated improvements, like the limitation of worst case precision for exp() and log() functions, based on the results of the paper Worst Cases for Correct Rounding of the Elementary Functions in Double Precision (PDF). One needs to prove that those results apply to the Glibc multiple precision bits.
Keep in mind: this is [w]hat the compiler tried to do; when you start down this path you are saying "that fancy compiler doesn't know what its doing, I'll do it all myself".
Trying to outsmart a compiler defeats much of the purpose of using one.
-- Kernighan and Plauger, The Elements of Programming Style
If it weren't for deadlines, nothing would be late.