345 lines
10 KiB
C
345 lines
10 KiB
C
/*
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* Mu-Law conversion Plug-In Interface
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* Copyright (c) 1999 by Jaroslav Kysela <perex@perex.cz>
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* Uros Bizjak <uros@kss-loka.si>
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*
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* Based on reference implementation by Sun Microsystems, Inc.
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*
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* This library is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Library General Public License as
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* published by the Free Software Foundation; either version 2 of
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* the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Library General Public License for more details.
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*
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* You should have received a copy of the GNU Library General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*
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*/
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#include <linux/time.h>
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#include <sound/core.h>
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#include <sound/pcm.h>
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#include "pcm_plugin.h"
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#define SIGN_BIT (0x80) /* Sign bit for a u-law byte. */
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#define QUANT_MASK (0xf) /* Quantization field mask. */
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#define NSEGS (8) /* Number of u-law segments. */
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#define SEG_SHIFT (4) /* Left shift for segment number. */
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#define SEG_MASK (0x70) /* Segment field mask. */
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static inline int val_seg(int val)
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{
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int r = 0;
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val >>= 7;
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if (val & 0xf0) {
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val >>= 4;
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r += 4;
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}
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if (val & 0x0c) {
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val >>= 2;
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r += 2;
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}
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if (val & 0x02)
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r += 1;
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return r;
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}
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#define BIAS (0x84) /* Bias for linear code. */
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/*
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* linear2ulaw() - Convert a linear PCM value to u-law
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*
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* In order to simplify the encoding process, the original linear magnitude
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* is biased by adding 33 which shifts the encoding range from (0 - 8158) to
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* (33 - 8191). The result can be seen in the following encoding table:
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*
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* Biased Linear Input Code Compressed Code
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* ------------------------ ---------------
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* 00000001wxyza 000wxyz
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* 0000001wxyzab 001wxyz
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* 000001wxyzabc 010wxyz
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* 00001wxyzabcd 011wxyz
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* 0001wxyzabcde 100wxyz
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* 001wxyzabcdef 101wxyz
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* 01wxyzabcdefg 110wxyz
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* 1wxyzabcdefgh 111wxyz
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*
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* Each biased linear code has a leading 1 which identifies the segment
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* number. The value of the segment number is equal to 7 minus the number
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* of leading 0's. The quantization interval is directly available as the
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* four bits wxyz. * The trailing bits (a - h) are ignored.
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*
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* Ordinarily the complement of the resulting code word is used for
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* transmission, and so the code word is complemented before it is returned.
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*
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* For further information see John C. Bellamy's Digital Telephony, 1982,
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* John Wiley & Sons, pps 98-111 and 472-476.
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*/
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static unsigned char linear2ulaw(int pcm_val) /* 2's complement (16-bit range) */
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{
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int mask;
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int seg;
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unsigned char uval;
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/* Get the sign and the magnitude of the value. */
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if (pcm_val < 0) {
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pcm_val = BIAS - pcm_val;
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mask = 0x7F;
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} else {
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pcm_val += BIAS;
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mask = 0xFF;
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}
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if (pcm_val > 0x7FFF)
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pcm_val = 0x7FFF;
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/* Convert the scaled magnitude to segment number. */
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seg = val_seg(pcm_val);
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/*
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* Combine the sign, segment, quantization bits;
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* and complement the code word.
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*/
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uval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0xF);
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return uval ^ mask;
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}
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/*
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* ulaw2linear() - Convert a u-law value to 16-bit linear PCM
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*
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* First, a biased linear code is derived from the code word. An unbiased
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* output can then be obtained by subtracting 33 from the biased code.
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*
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* Note that this function expects to be passed the complement of the
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* original code word. This is in keeping with ISDN conventions.
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*/
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static int ulaw2linear(unsigned char u_val)
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{
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int t;
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/* Complement to obtain normal u-law value. */
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u_val = ~u_val;
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/*
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* Extract and bias the quantization bits. Then
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* shift up by the segment number and subtract out the bias.
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*/
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t = ((u_val & QUANT_MASK) << 3) + BIAS;
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t <<= ((unsigned)u_val & SEG_MASK) >> SEG_SHIFT;
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return ((u_val & SIGN_BIT) ? (BIAS - t) : (t - BIAS));
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}
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/*
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* Basic Mu-Law plugin
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*/
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typedef void (*mulaw_f)(struct snd_pcm_plugin *plugin,
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const struct snd_pcm_plugin_channel *src_channels,
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struct snd_pcm_plugin_channel *dst_channels,
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snd_pcm_uframes_t frames);
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struct mulaw_priv {
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mulaw_f func;
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int cvt_endian; /* need endian conversion? */
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unsigned int native_ofs; /* byte offset in native format */
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unsigned int copy_ofs; /* byte offset in s16 format */
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unsigned int native_bytes; /* byte size of the native format */
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unsigned int copy_bytes; /* bytes to copy per conversion */
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u16 flip; /* MSB flip for signedness, done after endian conversion */
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};
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static inline void cvt_s16_to_native(struct mulaw_priv *data,
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unsigned char *dst, u16 sample)
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{
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sample ^= data->flip;
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if (data->cvt_endian)
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sample = swab16(sample);
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if (data->native_bytes > data->copy_bytes)
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memset(dst, 0, data->native_bytes);
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memcpy(dst + data->native_ofs, (char *)&sample + data->copy_ofs,
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data->copy_bytes);
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}
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static void mulaw_decode(struct snd_pcm_plugin *plugin,
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const struct snd_pcm_plugin_channel *src_channels,
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struct snd_pcm_plugin_channel *dst_channels,
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snd_pcm_uframes_t frames)
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{
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struct mulaw_priv *data = (struct mulaw_priv *)plugin->extra_data;
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int channel;
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int nchannels = plugin->src_format.channels;
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for (channel = 0; channel < nchannels; ++channel) {
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char *src;
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char *dst;
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int src_step, dst_step;
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snd_pcm_uframes_t frames1;
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if (!src_channels[channel].enabled) {
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if (dst_channels[channel].wanted)
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snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format);
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dst_channels[channel].enabled = 0;
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continue;
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}
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dst_channels[channel].enabled = 1;
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src = src_channels[channel].area.addr + src_channels[channel].area.first / 8;
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dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8;
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src_step = src_channels[channel].area.step / 8;
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dst_step = dst_channels[channel].area.step / 8;
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frames1 = frames;
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while (frames1-- > 0) {
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signed short sample = ulaw2linear(*src);
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cvt_s16_to_native(data, dst, sample);
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src += src_step;
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dst += dst_step;
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}
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}
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}
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static inline signed short cvt_native_to_s16(struct mulaw_priv *data,
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unsigned char *src)
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{
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u16 sample = 0;
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memcpy((char *)&sample + data->copy_ofs, src + data->native_ofs,
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data->copy_bytes);
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if (data->cvt_endian)
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sample = swab16(sample);
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sample ^= data->flip;
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return (signed short)sample;
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}
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static void mulaw_encode(struct snd_pcm_plugin *plugin,
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const struct snd_pcm_plugin_channel *src_channels,
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struct snd_pcm_plugin_channel *dst_channels,
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snd_pcm_uframes_t frames)
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{
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struct mulaw_priv *data = (struct mulaw_priv *)plugin->extra_data;
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int channel;
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int nchannels = plugin->src_format.channels;
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for (channel = 0; channel < nchannels; ++channel) {
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char *src;
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char *dst;
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int src_step, dst_step;
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snd_pcm_uframes_t frames1;
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if (!src_channels[channel].enabled) {
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if (dst_channels[channel].wanted)
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snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format);
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dst_channels[channel].enabled = 0;
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continue;
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}
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dst_channels[channel].enabled = 1;
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src = src_channels[channel].area.addr + src_channels[channel].area.first / 8;
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dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8;
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src_step = src_channels[channel].area.step / 8;
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dst_step = dst_channels[channel].area.step / 8;
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frames1 = frames;
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while (frames1-- > 0) {
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signed short sample = cvt_native_to_s16(data, src);
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*dst = linear2ulaw(sample);
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src += src_step;
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dst += dst_step;
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}
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}
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}
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static snd_pcm_sframes_t mulaw_transfer(struct snd_pcm_plugin *plugin,
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const struct snd_pcm_plugin_channel *src_channels,
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struct snd_pcm_plugin_channel *dst_channels,
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snd_pcm_uframes_t frames)
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{
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struct mulaw_priv *data;
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if (snd_BUG_ON(!plugin || !src_channels || !dst_channels))
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return -ENXIO;
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if (frames == 0)
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return 0;
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#ifdef CONFIG_SND_DEBUG
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{
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unsigned int channel;
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for (channel = 0; channel < plugin->src_format.channels; channel++) {
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if (snd_BUG_ON(src_channels[channel].area.first % 8 ||
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src_channels[channel].area.step % 8))
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return -ENXIO;
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if (snd_BUG_ON(dst_channels[channel].area.first % 8 ||
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dst_channels[channel].area.step % 8))
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return -ENXIO;
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}
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}
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#endif
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data = (struct mulaw_priv *)plugin->extra_data;
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data->func(plugin, src_channels, dst_channels, frames);
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return frames;
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}
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static void init_data(struct mulaw_priv *data, snd_pcm_format_t format)
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{
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#ifdef SNDRV_LITTLE_ENDIAN
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data->cvt_endian = snd_pcm_format_big_endian(format) > 0;
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#else
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data->cvt_endian = snd_pcm_format_little_endian(format) > 0;
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#endif
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if (!snd_pcm_format_signed(format))
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data->flip = 0x8000;
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data->native_bytes = snd_pcm_format_physical_width(format) / 8;
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data->copy_bytes = data->native_bytes < 2 ? 1 : 2;
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if (snd_pcm_format_little_endian(format)) {
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data->native_ofs = data->native_bytes - data->copy_bytes;
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data->copy_ofs = 2 - data->copy_bytes;
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} else {
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/* S24 in 4bytes need an 1 byte offset */
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data->native_ofs = data->native_bytes -
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snd_pcm_format_width(format) / 8;
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}
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}
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int snd_pcm_plugin_build_mulaw(struct snd_pcm_substream *plug,
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struct snd_pcm_plugin_format *src_format,
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struct snd_pcm_plugin_format *dst_format,
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struct snd_pcm_plugin **r_plugin)
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{
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int err;
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struct mulaw_priv *data;
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struct snd_pcm_plugin *plugin;
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struct snd_pcm_plugin_format *format;
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mulaw_f func;
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if (snd_BUG_ON(!r_plugin))
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return -ENXIO;
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*r_plugin = NULL;
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if (snd_BUG_ON(src_format->rate != dst_format->rate))
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return -ENXIO;
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if (snd_BUG_ON(src_format->channels != dst_format->channels))
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return -ENXIO;
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if (dst_format->format == SNDRV_PCM_FORMAT_MU_LAW) {
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format = src_format;
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func = mulaw_encode;
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}
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else if (src_format->format == SNDRV_PCM_FORMAT_MU_LAW) {
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format = dst_format;
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func = mulaw_decode;
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}
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else {
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snd_BUG();
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return -EINVAL;
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}
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if (snd_BUG_ON(!snd_pcm_format_linear(format->format)))
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return -ENXIO;
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err = snd_pcm_plugin_build(plug, "Mu-Law<->linear conversion",
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src_format, dst_format,
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sizeof(struct mulaw_priv), &plugin);
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if (err < 0)
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return err;
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data = (struct mulaw_priv *)plugin->extra_data;
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data->func = func;
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init_data(data, format->format);
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plugin->transfer = mulaw_transfer;
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*r_plugin = plugin;
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return 0;
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}
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