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| author | Loren Merritt <lorenm@u.washington.edu> | 2007-09-29 05:41:27 +0000 |
|---|---|---|
| committer | Loren Merritt <lorenm@u.washington.edu> | 2007-09-29 05:41:27 +0000 |
| commit | 14bd2a9f25fc0de4fb1a2d4afaef09162c51bb35 (patch) | |
| tree | 83c7e0dc6971c767b00d046fd43a733d39c98ef9 /libavcodec/flacenc.c | |
| parent | f6215b1b069680a782ca28058b3ec6d9bb4a45e1 (diff) | |
replace brute force find_optimal_param() with a closed-form solution.
overall flac encoding: 4-15% faster.
output is not identical to the previous algorithm due to occasional rounding
errors, but the differece is less than .0005% bitrate.
Originally committed as revision 10612 to svn://svn.ffmpeg.org/ffmpeg/trunk
Diffstat (limited to 'libavcodec/flacenc.c')
| -rw-r--r-- | libavcodec/flacenc.c | 23 |
1 files changed, 11 insertions, 12 deletions
diff --git a/libavcodec/flacenc.c b/libavcodec/flacenc.c index e997bca129..3b01a3ba1a 100644 --- a/libavcodec/flacenc.c +++ b/libavcodec/flacenc.c @@ -447,20 +447,19 @@ static void copy_samples(FlacEncodeContext *s, int16_t *samples) #define rice_encode_count(sum, n, k) (((n)*((k)+1))+((sum-(n>>1))>>(k))) +/** + * Solve for d/dk(rice_encode_count) = n-((sum-(n>>1))>>(k+1)) = 0 + */ static int find_optimal_param(uint32_t sum, int n) { - int k, k_opt; - uint32_t nbits[MAX_RICE_PARAM+1]; - - k_opt = 0; - nbits[0] = UINT32_MAX; - for(k=0; k<=MAX_RICE_PARAM; k++) { - nbits[k] = rice_encode_count(sum, n, k); - if(nbits[k] < nbits[k_opt]) { - k_opt = k; - } - } - return k_opt; + int k; + uint32_t sum2; + + if(sum <= n>>1) + return 0; + sum2 = sum-(n>>1); + k = av_log2(n<256 ? FASTDIV(sum2,n) : sum2/n); + return FFMIN(k, MAX_RICE_PARAM); } static uint32_t calc_optimal_rice_params(RiceContext *rc, int porder, |