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| author | Stefano Sabatini <stefano.sabatini-lala@poste.it> | 2009-12-12 16:24:37 +0000 |
|---|---|---|
| committer | Stefano Sabatini <stefano.sabatini-lala@poste.it> | 2009-12-12 16:24:37 +0000 |
| commit | 3ba69a15c680596feeef1d213ce2b85823dde985 (patch) | |
| tree | f0921738d1342b2c1edd70c69cd54a8bd771d9a4 | |
| parent | 62d75662391733cb97edfe1ed000afe2360bc0f3 (diff) | |
| download | ffmpeg-3ba69a15c680596feeef1d213ce2b85823dde985.tar.gz | |
Implement av_bmg_next(), a Box-Muller Gaussian random generator.
See the thread:
"[FFmpeg-devel] [PATCH] Box-Muller gaussian generator".
Originally committed as revision 20808 to svn://svn.ffmpeg.org/ffmpeg/trunk
| -rw-r--r-- | libavutil/avutil.h | 4 | ||||
| -rw-r--r-- | libavutil/lfg.c | 33 | ||||
| -rw-r--r-- | libavutil/lfg.h | 8 |
3 files changed, 43 insertions, 2 deletions
diff --git a/libavutil/avutil.h b/libavutil/avutil.h index d799211ffc..0a398680f4 100644 --- a/libavutil/avutil.h +++ b/libavutil/avutil.h @@ -35,8 +35,8 @@ #define AV_VERSION(a, b, c) AV_VERSION_DOT(a, b, c) #define LIBAVUTIL_VERSION_MAJOR 50 -#define LIBAVUTIL_VERSION_MINOR 5 -#define LIBAVUTIL_VERSION_MICRO 1 +#define LIBAVUTIL_VERSION_MINOR 6 +#define LIBAVUTIL_VERSION_MICRO 0 #define LIBAVUTIL_VERSION_INT AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \ LIBAVUTIL_VERSION_MINOR, \ diff --git a/libavutil/lfg.c b/libavutil/lfg.c index e876d18fef..a6828634ae 100644 --- a/libavutil/lfg.c +++ b/libavutil/lfg.c @@ -39,6 +39,21 @@ void av_cold av_lfg_init(AVLFG *c, unsigned int seed){ c->index=0; } +void av_bmg_get(AVLFG *lfg, double out[2]) +{ + double x1, x2, w; + + do { + x1 = 2.0/UINT_MAX*av_lfg_get(lfg) - 1.0; + x2 = 2.0/UINT_MAX*av_lfg_get(lfg) - 1.0; + w = x1*x1 + x2*x2; + } while (w >= 1.0); + + w = sqrt((-2.0 * log(w)) / w); + out[0] = x1 * w; + out[1] = x2 * w; +} + #ifdef TEST #include "log.h" #include "common.h" @@ -59,6 +74,24 @@ int main(void) STOP_TIMER("624 calls of av_lfg_get"); } av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x); + + /* BMG usage example */ + { + double mean = 1000; + double stddev = 53; + + av_lfg_init(&state, 42); + + for (i = 0; i < 1000; i += 2) { + double bmg_out[2]; + av_bmg_get(&state, bmg_out); + av_log(NULL, AV_LOG_INFO, + "%f\n%f\n", + bmg_out[0] * stddev + mean, + bmg_out[1] * stddev + mean); + } + } + return 0; } #endif diff --git a/libavutil/lfg.h b/libavutil/lfg.h index 3250c18e79..ac89d120d5 100644 --- a/libavutil/lfg.h +++ b/libavutil/lfg.h @@ -51,4 +51,12 @@ static inline unsigned int av_mlfg_get(AVLFG *c){ return c->state[c->index++ & 63] = 2*a*b+a+b; } +/** + * Gets the next two numbers generated by a Box-Muller Gaussian + * generator using the random numbers issued by lfg. + * + * @param out[2] array where are placed the two generated numbers + */ +void av_bmg_get(AVLFG *lfg, double out[2]); + #endif /* AVUTIL_LFG_H */ |