diff options
| author | Max Kellermann <max@duempel.org> | 2009-01-03 14:51:47 +0100 |
|---|---|---|
| committer | Max Kellermann <max@duempel.org> | 2009-01-13 23:09:19 +0100 |
| commit | a0141dbe4f868413d78c94737846279124415479 (patch) | |
| tree | e917b22e3eced7f9a8d9a4fa9e1121b899246a86 | |
| parent | d93477d1369e55d76476952f30463461e47af443 (diff) | |
| download | mpd-a0141dbe4f868413d78c94737846279124415479.tar.gz mpd-a0141dbe4f868413d78c94737846279124415479.tar.xz mpd-a0141dbe4f868413d78c94737846279124415479.zip | |
pcm_utils: use the custom PRNG for volume dithering
Don't use libc's rand() function, because it is slow. Our own trivial
linear congruential generator is good enough for dithering.
| -rw-r--r-- | NEWS | 1 | ||||
| -rw-r--r-- | src/Makefile.am | 1 | ||||
| -rw-r--r-- | src/pcm_dither.c | 6 | ||||
| -rw-r--r-- | src/pcm_prng.h | 31 | ||||
| -rw-r--r-- | src/pcm_utils.c | 8 |
5 files changed, 41 insertions, 6 deletions
@@ -12,6 +12,7 @@ MPD 0.14.1 - not yet released * fix minor memory leak in decoder_tag() * fix cross-fading bug: it used to play some chunks of the new song twice * playlist: fix assertion failure during playlist load +* use custom PRNG for volume dithering (speedup) * detect libid3tag without pkg-config diff --git a/src/Makefile.am b/src/Makefile.am index ad4ad99f3..0699be50e 100644 --- a/src/Makefile.am +++ b/src/Makefile.am @@ -53,6 +53,7 @@ mpd_headers = \ pcm_channels.h \ pcm_resample.h \ pcm_dither.h \ + pcm_prng.h \ permission.h \ player_thread.h \ player_control.h \ diff --git a/src/pcm_dither.c b/src/pcm_dither.c index 1296d0926..984949685 100644 --- a/src/pcm_dither.c +++ b/src/pcm_dither.c @@ -17,11 +17,7 @@ */ #include "pcm_dither.h" - -static unsigned long prng(unsigned long state) -{ - return (state * 0x0019660dL + 0x3c6ef35fL) & 0xffffffffL; -} +#include "pcm_prng.h" static int16_t pcm_dither_sample_24_to_16(int32_t sample, struct pcm_dither_24 *dither) diff --git a/src/pcm_prng.h b/src/pcm_prng.h new file mode 100644 index 000000000..e961baacd --- /dev/null +++ b/src/pcm_prng.h @@ -0,0 +1,31 @@ +/* + * Copyright (C) 2003-2009 The Music Player Daemon Project + * http://www.musicpd.org + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + */ + +#ifndef PCM_PRNG_H +#define PCM_PRNG_H + +/** + * A very simple linear congruential PRNG. It's good enough for PCM + * dithering. + */ +static unsigned long prng(unsigned long state) +{ + return (state * 0x0019660dL + 0x3c6ef35fL) & 0xffffffffL; +} + +#endif diff --git a/src/pcm_utils.c b/src/pcm_utils.c index f73df8aef..3ce9b5fd0 100644 --- a/src/pcm_utils.c +++ b/src/pcm_utils.c @@ -18,6 +18,7 @@ #include "pcm_utils.h" #include "pcm_channels.h" +#include "pcm_prng.h" #include "log.h" #include "utils.h" #include "conf.h" @@ -31,7 +32,12 @@ static inline int pcm_dither(void) { - return (rand() & 511) - (rand() & 511); + static unsigned long state; + uint32_t r; + + r = state = prng(state); + + return (r & 511) - ((r >> 9) & 511); } /** |