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authorMax Kellermann <max@duempel.org>2009-01-03 14:51:47 +0100
committerMax Kellermann <max@duempel.org>2009-01-03 14:51:47 +0100
commit962f2407d2a3579b7125f937d93d04ccbeb9a453 (patch)
treee4e2fd55c02e53f94b3d63be8b8d2f714428f0b9 /src
parent8ebb3196a854d7e870bbbe904b534641df7d5f89 (diff)
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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 'src')
-rw-r--r--src/Makefile.am1
-rw-r--r--src/pcm_dither.c6
-rw-r--r--src/pcm_prng.h31
-rw-r--r--src/pcm_utils.c8
4 files changed, 40 insertions, 6 deletions
diff --git a/src/Makefile.am b/src/Makefile.am
index 1e1e82598..399534da8 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -54,6 +54,7 @@ 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 46c5f2884..a7e7a3990 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 "utils.h"
#include "conf.h"
#include "audio_format.h"
@@ -33,7 +34,12 @@
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);
}
/**