fast approximate function of exponential function exp and log
How to use
include fmath.hpp and use fmath::log, fmath::exp, fmath::expd.
fmath::PowGenerator is a class to generate a function to compute pow(x, y) of x >= 0 for a given fixed y > 0.
eg. fmath::PowGenerator f(1.234); f.get(x) returns pow(x, 1.234);
Prototpye of function
- float fmath::exp(float);
- float fmath::log(float);
- double fmath::logd(double);
- void fmath::logd_v(double *px, int n); // array version
- __m128 fmath::exp_ps(__m128);
- __m128 fmath::log_ps(__m128);
Experimental
If you install xbyak(http://homepage1.nifty.com/herumi/soft/xbyak_e.html) and define FMATH_USE_XBYAK before including fmath.hpp, then fmath::exp() and fmath::exp_ps() will be about 10~20 % faster. Xbyak version uses SSE4.1 if available.
AVX version of fmath::exp is experimental
Remark
gcc puts warnings such as "dereferencing type-punned pointer will break strict-aliasing rules." It is no problem. Please change #if 1 in fmath.hpp:423 if you worry about it. But it causes a little slower.
-ffast-math option of gcc may generate bad code for fmath::expd.
License
modified new BSD License http://opensource.org/licenses/BSD-3-Clause
History
- 2012/Oct/30 fix fmath::expd for small value
- 2011/Aug/26 add fmath::expd_v
- 2011/Mar/25 exp supports AVX
- 2011/Mar/25 exp, exp_ps support avx
- 2010/Feb/16 add fmath::exp_ps, log_ps and optimize functions
- 2010/Jan/10 add fmath::PowGenerator
- 2009/Dec/28 add fmath::log()
- 2009/Dec/09 support cygwin
- 2009/Dec/08 first version
Author
MITSUNARI Shigeo(herumi at nifty dot com) http://homepage1.nifty.com/herumi/soft/fmath.html
Benchmark
compiler
- Visual Studio 2010RC
- icc 11.1
- gcc 4.3.2 on cygwin
- gcc 4.4.1 on 64bit Linux
option
- cl(icl):
/Ox /Ob2 /GS- /Zi /D_SECURE_SCL=0 /MD /Oy /arch:SSE2 /fp:fast /DNOMINMAX
- gcc:
-O3 -fomit-frame-pointer -DNDEBUG -fno-operator-names -msse2 -mfpmath=sse -march=native
see fastexp.cpp or http://homepage1.nifty.com/herumi/soft/fmath.html