pcm_dither: added generic 24 to 16 bit dithering

Copied and adapted code from the mp3 decoder plugin.  This library now
replaces the old and low-quality function pcm_convert_24_to_16().

1 files changed, 41 insertions, 0 deletions

diff --git a/src/pcm_dither.h b/src/pcm_dither.h
new file mode 100644
index 000000000..202521497
--- /dev/null
+++ b/src/pcm_dither.h
@@ -0,0 +1,41 @@
+/* the Music Player Daemon (MPD)
+ * Copyright (C) 2008 Max Kellermann <max@duempel.org>
+ * This project's homepage is: 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_DITHER_H
+#define PCM_DITHER_H
+
+#include <stdint.h>
+
+struct pcm_dither_24 {
+	int32_t error[3];
+	int32_t random;
+};
+
+static inline void
+pcm_dither_24_init(struct pcm_dither_24 *dither)
+{
+	dither->error[0] = dither->error[1] = dither->error[2] = 0;
+	dither->random = 0;
+}
+
+void
+pcm_dither_24_to_16(struct pcm_dither_24 *dither,
+		    int16_t *dest, const int32_t *src,
+		    unsigned num_samples);
+
+#endif