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| 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.
Diffstat (limited to '')
| -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); } /** |