+/* plugin_common - Routines common to several plugins
+ * Copyright (C) 2002 Josh Coalson
+ *
+ * dithering routine derived from (other GPLed source):
+ * mad - MPEG audio decoder
+ * Copyright (C) 2000-2001 Robert Leslie
+ *
+ * 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 "dither.h"
+#include "FLAC/assert.h"
+
+#ifdef max
+#undef max
+#endif
+#define max(a,b) ((a)>(b)?(a):(b))
+
+
+#define FLAC__DO_DITHER
+
+#define MAX_SUPPORTED_CHANNELS 2
+
+#if defined _MSC_VER || defined __MINGW32__
+#define FLAC__INLINE __inline
+#else
+#define FLAC__INLINE
+#endif
+
+/* 32-bit pseudo-random number generator */
+static FLAC__INLINE FLAC__uint32 prng(FLAC__uint32 state)
+{
+ return (state * 0x0019660dL + 0x3c6ef35fL) & 0xffffffffL;
+}
+
+/* dither routine derived from MAD winamp plugin */
+
+typedef struct {
+ FLAC__int32 error[3];
+ FLAC__int32 random;
+} dither_state;
+
+static FLAC__INLINE FLAC__int32 linear_dither(unsigned source_bps, unsigned target_bps, FLAC__int32 sample, dither_state *dither, const FLAC__int32 MIN, const FLAC__int32 MAX)
+{
+ unsigned scalebits;
+ FLAC__int32 output, mask, random;
+
+ FLAC__ASSERT(source_bps < 32);
+ FLAC__ASSERT(target_bps <= 24);
+ FLAC__ASSERT(target_bps <= source_bps);
+
+ /* noise shape */
+ sample += dither->error[0] - dither->error[1] + dither->error[2];
+
+ dither->error[2] = dither->error[1];
+ dither->error[1] = dither->error[0] / 2;
+
+ /* bias */
+ output = sample + (1L << (source_bps - target_bps - 1));
+
+ scalebits = source_bps - target_bps;
+ mask = (1L << scalebits) - 1;
+
+ /* dither */
+ random = (FLAC__int32)prng(dither->random);
+ output += (random & mask) - (dither->random & mask);
+
+ dither->random = random;
+
+ /* clip */
+ if(output > MAX) {
+ output = MAX;
+
+ if(sample > MAX)
+ sample = MAX;
+ }
+ else if(output < MIN) {
+ output = MIN;
+
+ if(sample < MIN)
+ sample = MIN;
+ }
+
+ /* quantize */
+ output &= ~mask;
+
+ /* error feedback */
+ dither->error[0] = sample - output;
+
+ /* scale */
+ return output >> scalebits;
+}
+
+unsigned FLAC__plugin_common__pack_pcm(FLAC__byte *data, FLAC__int32 *input, unsigned wide_samples, unsigned channels, unsigned source_bps, unsigned target_bps)
+{
+ static dither_state dither[MAX_SUPPORTED_CHANNELS];
+ FLAC__byte * const start = data;
+ FLAC__int32 sample;
+ unsigned samples = wide_samples * channels;
+ const unsigned bytes_per_sample = target_bps / 8;
+
+ FLAC__ASSERT(MAX_SUPPORTED_CHANNELS == 2);
+ FLAC__ASSERT(channels > 0 && channels <= MAX_SUPPORTED_CHANNELS);
+ FLAC__ASSERT(source_bps < 32);
+ FLAC__ASSERT(target_bps <= 24);
+ FLAC__ASSERT(target_bps <= source_bps);
+ FLAC__ASSERT((source_bps & 7) == 0);
+ FLAC__ASSERT((target_bps & 7) == 0);
+
+ if(source_bps != target_bps) {
+ const FLAC__int32 MIN = -(1L << source_bps);
+ const FLAC__int32 MAX = ~MIN; /*(1L << (source_bps-1)) - 1 */
+ const unsigned dither_twiggle = channels - 1;
+ unsigned dither_source = 0;
+
+ while(samples--) {
+ sample = linear_dither(source_bps, target_bps, *input++, &dither[dither_source], MIN, MAX);
+ dither_source ^= dither_twiggle;
+
+ switch(target_bps) {
+ case 8:
+ data[0] = sample ^ 0x80;
+ break;
+ case 24:
+ data[2] = (FLAC__byte)(sample >> 16);
+ /* fall through */
+ case 16:
+ data[1] = (FLAC__byte)(sample >> 8);
+ data[0] = (FLAC__byte)sample;
+ }
+
+ data += bytes_per_sample;
+ }
+ }
+ else {
+ while(samples--) {
+ sample = *input++;
+
+ switch(target_bps) {
+ case 8:
+ data[0] = sample ^ 0x80;
+ break;
+ case 24:
+ data[2] = (FLAC__byte)(sample >> 16);
+ /* fall through */
+ case 16:
+ data[1] = (FLAC__byte)(sample >> 8);
+ data[0] = (FLAC__byte)sample;
+ }
+
+ data += bytes_per_sample;
+ }
+ }
+
+ return data - start;
+}