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-rw-r--r--src/Makefile.am2
-rw-r--r--src/pcm_dither.c82
-rw-r--r--src/pcm_dither.h41
-rw-r--r--src/pcm_utils.c18
-rw-r--r--src/pcm_utils.h4
5 files changed, 139 insertions, 8 deletions
diff --git a/src/Makefile.am b/src/Makefile.am
index 17234ca3..f2bf55eb 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -66,6 +66,7 @@ mpd_headers = \
path.h \
mapper.h \
pcm_utils.h \
+ pcm_dither.h \
permission.h \
player_thread.h \
player_control.h \
@@ -145,6 +146,7 @@ mpd_SOURCES = \
path.c \
mapper.c \
pcm_utils.c \
+ pcm_dither.c \
permission.c \
player_thread.c \
player_control.c \
diff --git a/src/pcm_dither.c b/src/pcm_dither.c
new file mode 100644
index 00000000..1296d092
--- /dev/null
+++ b/src/pcm_dither.c
@@ -0,0 +1,82 @@
+/* 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
+ */
+
+#include "pcm_dither.h"
+
+static unsigned long prng(unsigned long state)
+{
+ return (state * 0x0019660dL + 0x3c6ef35fL) & 0xffffffffL;
+}
+
+static int16_t
+pcm_dither_sample_24_to_16(int32_t sample, struct pcm_dither_24 *dither)
+{
+ int32_t output, rnd;
+
+ enum {
+ from_bits = 24,
+ to_bits = 16,
+ scale_bits = from_bits - to_bits,
+ round = 1 << (scale_bits - 1),
+ mask = (1 << scale_bits) - 1,
+ ONE = 1 << (from_bits - 1),
+ MIN = -ONE,
+ MAX = ONE - 1
+ };
+
+ sample += dither->error[0] - dither->error[1] + dither->error[2];
+
+ dither->error[2] = dither->error[1];
+ dither->error[1] = dither->error[0] / 2;
+
+ /* round */
+ output = sample + round;
+
+ rnd = prng(dither->random);
+ output += (rnd & mask) - (dither->random & mask);
+
+ dither->random = rnd;
+
+ /* clip */
+ if (output > MAX) {
+ output = MAX;
+
+ if (sample > MAX)
+ sample = MAX;
+ } else if (output < MIN) {
+ output = MIN;
+
+ if (sample < MIN)
+ sample = MIN;
+ }
+
+ output &= ~mask;
+
+ dither->error[0] = sample - output;
+
+ return (int16_t)(output >> scale_bits);
+}
+
+void
+pcm_dither_24_to_16(struct pcm_dither_24 *dither,
+ int16_t *dest, const int32_t *src,
+ unsigned num_samples)
+{
+ while (num_samples-- > 0)
+ *dest++ = pcm_dither_sample_24_to_16(*src++, dither);
+}
diff --git a/src/pcm_dither.h b/src/pcm_dither.h
new file mode 100644
index 00000000..20252149
--- /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
diff --git a/src/pcm_utils.c b/src/pcm_utils.c
index bd7fc048..8d5bed99 100644
--- a/src/pcm_utils.c
+++ b/src/pcm_utils.c
@@ -208,6 +208,8 @@ void pcm_mix(char *buffer1, const char *buffer2, size_t size,
void pcm_convert_init(struct pcm_convert_state *state)
{
memset(state, 0, sizeof(*state));
+
+ pcm_dither_24_init(&state->dither);
}
#ifdef HAVE_LIBSAMPLERATE
@@ -457,17 +459,16 @@ pcm_convert_8_to_16(int16_t *out, const int8_t *in,
}
static void
-pcm_convert_24_to_16(int16_t *out, const int32_t *in,
+pcm_convert_24_to_16(struct pcm_dither_24 *dither,
+ int16_t *out, const int32_t *in,
unsigned num_samples)
{
- while (num_samples > 0) {
- *out++ = *in++ >> 8;
- --num_samples;
- }
+ pcm_dither_24_to_16(dither, out, in, num_samples);
}
static const int16_t *
-pcm_convert_to_16(uint8_t bits, const void *src,
+pcm_convert_to_16(struct pcm_convert_state *convert,
+ uint8_t bits, const void *src,
size_t src_size, size_t *dest_size_r)
{
static int16_t *buf;
@@ -500,7 +501,8 @@ pcm_convert_to_16(uint8_t bits, const void *src,
buf = xrealloc(buf, len);
}
- pcm_convert_24_to_16((int16_t *)buf,
+ pcm_convert_24_to_16(&convert->dither,
+ (int16_t *)buf,
(const int32_t *)src,
num_samples);
return buf;
@@ -524,7 +526,7 @@ size_t pcm_convert(const struct audio_format *inFormat,
assert(outFormat->bits == 16);
/* everything else supports 16 bit only, so convert to that first */
- buf = pcm_convert_to_16(inFormat->bits, src, src_size, &len);
+ buf = pcm_convert_to_16(convState, inFormat->bits, src, src_size, &len);
if (!buf)
exit(EXIT_FAILURE);
diff --git a/src/pcm_utils.h b/src/pcm_utils.h
index 3fc15e8b..835ba187 100644
--- a/src/pcm_utils.h
+++ b/src/pcm_utils.h
@@ -20,6 +20,7 @@
#define PCM_UTILS_H
#include "../config.h"
+#include "pcm_dither.h"
#include <stdint.h>
#include <stddef.h>
@@ -40,6 +41,9 @@ struct pcm_convert_state {
uint32_t lastInSampleRate;
uint32_t lastOutSampleRate;
#endif
+
+ struct pcm_dither_24 dither;
+
/* Strict C99 doesn't allow empty structs */
int error;
};
generated by cgit v1.2.3 (git 2.39.1) at 2024-06-25 23:33:27 +0000