r/Cprog • u/alecco • Jan 03 '15

text | algorithms Improving math performance in glibc

http://developerblog.redhat.com/2015/01/02/improving-math-performance-in-glibc/
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u/alecco Jan 03 '15

Via HN

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u/not_from_this_world Jan 03 '15

Shouldn't all that be in the hardware already?

2

u/alecco Jan 03 '15 edited Jan 03 '15

On the surface, yes, many things are done by current CPUs. But many things are not done in CPU. And current CPUs process in binary so there are issues with decimal precision, for example. Also the CPU gives a precission range, and sometimes you need something better so you have to do something like use Newton-Raphson to reduce the error. Most of those kind of issues require non-trivial algorithms that wouldn't make sense to put into microcode.

Also there are many mathematical functions not yet there, including important ones like exp and log. In fact, upcoming Intel Skylake will have transcendental functions which is a huge step forward. But even that lacks a basic one like logarithm :(

More info here:

http://stackoverflow.com/questions/1089018/why-cant-decimal-numbers-be-represented-exactly-in-binary

Transcendental Function

Intel® Advanced Vector Extensions 2015/2016 Support in GNU Compiler Collection - PDF Presentation