ffmath.h (2073B)
1 /* 2 * copyright (c) 2016 Ganesh Ajjanagadde <gajjanag@gmail.com> 3 * 4 * This file is part of FFmpeg. 5 * 6 * FFmpeg is free software; you can redistribute it and/or 7 * modify it under the terms of the GNU Lesser General Public 8 * License as published by the Free Software Foundation; either 9 * version 2.1 of the License, or (at your option) any later version. 10 * 11 * FFmpeg is distributed in the hope that it will be useful, 12 * but WITHOUT ANY WARRANTY; without even the implied warranty of 13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14 * Lesser General Public License for more details. 15 * 16 * You should have received a copy of the GNU Lesser General Public 17 * License along with FFmpeg; if not, write to the Free Software 18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 19 */ 20 21 /** 22 * @file 23 * internal math functions header 24 */ 25 26 #ifndef AVUTIL_FFMATH_H 27 #define AVUTIL_FFMATH_H 28 29 #include "attributes.h" 30 #include "libm.h" 31 32 /** 33 * Compute 10^x for floating point values. Note: this function is by no means 34 * "correctly rounded", and is meant as a fast, reasonably accurate approximation. 35 * For instance, maximum relative error for the double precision variant is 36 * ~ 1e-13 for very small and very large values. 37 * This is ~2x faster than GNU libm's approach, which is still off by 2ulp on 38 * some inputs. 39 * @param x exponent 40 * @return 10^x 41 */ 42 static av_always_inline double ff_exp10(double x) 43 { 44 return exp2(M_LOG2_10 * x); 45 } 46 47 static av_always_inline float ff_exp10f(float x) 48 { 49 return exp2f(M_LOG2_10 * x); 50 } 51 52 /** 53 * Compute x^y for floating point x, y. Note: this function is faster than the 54 * libm variant due to mainly 2 reasons: 55 * 1. It does not handle any edge cases. In particular, this is only guaranteed 56 * to work correctly for x > 0. 57 * 2. It is not as accurate as a standard nearly "correctly rounded" libm variant. 58 * @param x base 59 * @param y exponent 60 * @return x^y 61 */ 62 static av_always_inline float ff_fast_powf(float x, float y) 63 { 64 return expf(logf(x) * y); 65 } 66 67 #endif /* AVUTIL_FFMATH_H */