diff options
| -rw-r--r-- | src/pcm_volume.c | 41 |
1 files changed, 40 insertions, 1 deletions
diff --git a/src/pcm_volume.c b/src/pcm_volume.c index 2dff14ef..cb1d82b0 100644 --- a/src/pcm_volume.c +++ b/src/pcm_volume.c @@ -58,16 +58,55 @@ pcm_volume_change_16(int16_t *buffer, unsigned num_samples, int volume) } } +#if __i386__ +/** + * Optimized volume function for i386. Use the EDX:EAX 2*32 bit + * multiplication result instead of emulating 64 bit multiplication. + */ +static inline int32_t +pcm_volume_sample_24(int32_t sample, int32_t volume, int32_t dither) +{ + int32_t result; + + asm(/* edx:eax = sample * volume */ + "imul %2\n" + + /* "add %3, %1\n" dithering disabled for now, because we + have no overflow check - is dithering really important + here? */ + + /* eax = edx:eax / PCM_VOLUME_1 */ + "sal $22, %%edx\n" + "shr $10, %1\n" + "or %%edx, %1\n" + + : "=a"(result) + : "0"(sample), "r"(volume) /* , "r"(dither) */ + : "edx" + ); + + return result; +} +#endif + static void pcm_volume_change_24(int32_t *buffer, unsigned num_samples, int volume) { while (num_samples > 0) { +#if __i386__ + /* assembly version for i386 */ + int32_t sample = *buffer; + + sample = pcm_volume_sample_24(sample, volume, + pcm_volume_dither()); +#else + /* portable version */ int64_t sample = *buffer; sample = (sample * volume + pcm_volume_dither() + PCM_VOLUME_1 / 2) / PCM_VOLUME_1; - +#endif *buffer++ = pcm_range(sample, 24); --num_samples; } |