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.

1 files changed, 31 insertions, 0 deletions

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