/* * Mu-Law conversion Plug-In Interface * Copyright (c) 1999 by Jaroslav Kysela * Uros Bizjak * * Based on reference implementation by Sun Microsystems, Inc. * * This library is free software; you can redistribute it and/or modify * it under the terms of the GNU Library 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 Library General Public License for more details. * * You should have received a copy of the GNU Library General Public * License along with this library; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA * */ #include #include #include #include "pcm_plugin.h" #define SIGN_BIT (0x80) /* Sign bit for a u-law byte. */ #define QUANT_MASK (0xf) /* Quantization field mask. */ #define NSEGS (8) /* Number of u-law segments. */ #define SEG_SHIFT (4) /* Left shift for segment number. */ #define SEG_MASK (0x70) /* Segment field mask. */ static inline int val_seg(int val) { int r = 0; val >>= 7; if (val & 0xf0) { val >>= 4; r += 4; } if (val & 0x0c) { val >>= 2; r += 2; } if (val & 0x02) r += 1; return r; } #define BIAS (0x84) /* Bias for linear code. */ /* * linear2ulaw() - Convert a linear PCM value to u-law * * In order to simplify the encoding process, the original linear magnitude * is biased by adding 33 which shifts the encoding range from (0 - 8158) to * (33 - 8191). The result can be seen in the following encoding table: * * Biased Linear Input Code Compressed Code * ------------------------ --------------- * 00000001wxyza 000wxyz * 0000001wxyzab 001wxyz * 000001wxyzabc 010wxyz * 00001wxyzabcd 011wxyz * 0001wxyzabcde 100wxyz * 001wxyzabcdef 101wxyz * 01wxyzabcdefg 110wxyz * 1wxyzabcdefgh 111wxyz * * Each biased linear code has a leading 1 which identifies the segment * number. The value of the segment number is equal to 7 minus the number * of leading 0's. The quantization interval is directly available as the * four bits wxyz. * The trailing bits (a - h) are ignored. * * Ordinarily the complement of the resulting code word is used for * transmission, and so the code word is complemented before it is returned. * * For further information see John C. Bellamy's Digital Telephony, 1982, * John Wiley & Sons, pps 98-111 and 472-476. */ static unsigned char linear2ulaw(int pcm_val) /* 2's complement (16-bit range) */ { int mask; int seg; unsigned char uval; /* Get the sign and the magnitude of the value. */ if (pcm_val < 0) { pcm_val = BIAS - pcm_val; mask = 0x7F; } else { pcm_val += BIAS; mask = 0xFF; } if (pcm_val > 0x7FFF) pcm_val = 0x7FFF; /* Convert the scaled magnitude to segment number. */ seg = val_seg(pcm_val); /* * Combine the sign, segment, quantization bits; * and complement the code word. */ uval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0xF); return uval ^ mask; } /* * ulaw2linear() - Convert a u-law value to 16-bit linear PCM * * First, a biased linear code is derived from the code word. An unbiased * output can then be obtained by subtracting 33 from the biased code. * * Note that this function expects to be passed the complement of the * original code word. This is in keeping with ISDN conventions. */ static int ulaw2linear(unsigned char u_val) { int t; /* Complement to obtain normal u-law value. */ u_val = ~u_val; /* * Extract and bias the quantization bits. Then * shift up by the segment number and subtract out the bias. */ t = ((u_val & QUANT_MASK) << 3) + BIAS; t <<= ((unsigned)u_val & SEG_MASK) >> SEG_SHIFT; return ((u_val & SIGN_BIT) ? (BIAS - t) : (t - BIAS)); } /* * Basic Mu-Law plugin */ typedef void (*mulaw_f)(struct snd_pcm_plugin *plugin, const struct snd_pcm_plugin_channel *src_channels, struct snd_pcm_plugin_channel *dst_channels, snd_pcm_uframes_t frames); struct mulaw_priv { mulaw_f func; int cvt_endian; /* need endian conversion? */ unsigned int native_ofs; /* byte offset in native format */ unsigned int copy_ofs; /* byte offset in s16 format */ unsigned int native_bytes; /* byte size of the native format */ unsigned int copy_bytes; /* bytes to copy per conversion */ u16 flip; /* MSB flip for signedness, done after endian conversion */ }; static inline void cvt_s16_to_native(struct mulaw_priv *data, unsigned char *dst, u16 sample) { sample ^= data->flip; if (data->cvt_endian) sample = swab16(sample); if (data->native_bytes > data->copy_bytes) memset(dst, 0, data->native_bytes); memcpy(dst + data->native_ofs, (char *)&sample + data->copy_ofs, data->copy_bytes); } static void mulaw_decode(struct snd_pcm_plugin *plugin, const struct snd_pcm_plugin_channel *src_channels, struct snd_pcm_plugin_channel *dst_channels, snd_pcm_uframes_t frames) { struct mulaw_priv *data = (struct mulaw_priv *)plugin->extra_data; int channel; int nchannels = plugin->src_format.channels; for (channel = 0; channel < nchannels; ++channel) { char *src; char *dst; int src_step, dst_step; snd_pcm_uframes_t frames1; if (!src_channels[channel].enabled) { if (dst_channels[channel].wanted) snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format); dst_channels[channel].enabled = 0; continue; } dst_channels[channel].enabled = 1; src = src_channels[channel].area.addr + src_channels[channel].area.first / 8; dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8; src_step = src_channels[channel].area.step / 8; dst_step = dst_channels[channel].area.step / 8; frames1 = frames; while (frames1-- > 0) { signed short sample = ulaw2linear(*src); cvt_s16_to_native(data, dst, sample); src += src_step; dst += dst_step; } } } static inline signed short cvt_native_to_s16(struct mulaw_priv *data, unsigned char *src) { u16 sample = 0; memcpy((char *)&sample + data->copy_ofs, src + data->native_ofs, data->copy_bytes); if (data->cvt_endian) sample = swab16(sample); sample ^= data->flip; return (signed short)sample; } static void mulaw_encode(struct snd_pcm_plugin *plugin, const struct snd_pcm_plugin_channel *src_channels, struct snd_pcm_plugin_channel *dst_channels, snd_pcm_uframes_t frames) { struct mulaw_priv *data = (struct mulaw_priv *)plugin->extra_data; int channel; int nchannels = plugin->src_format.channels; for (channel = 0; channel < nchannels; ++channel) { char *src; char *dst; int src_step, dst_step; snd_pcm_uframes_t frames1; if (!src_channels[channel].enabled) { if (dst_channels[channel].wanted) snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format); dst_channels[channel].enabled = 0; continue; } dst_channels[channel].enabled = 1; src = src_channels[channel].area.addr + src_channels[channel].area.first / 8; dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8; src_step = src_channels[channel].area.step / 8; dst_step = dst_channels[channel].area.step / 8; frames1 = frames; while (frames1-- > 0) { signed short sample = cvt_native_to_s16(data, src); *dst = linear2ulaw(sample); src += src_step; dst += dst_step; } } } static snd_pcm_sframes_t mulaw_transfer(struct snd_pcm_plugin *plugin, const struct snd_pcm_plugin_channel *src_channels, struct snd_pcm_plugin_channel *dst_channels, snd_pcm_uframes_t frames) { struct mulaw_priv *data; snd_assert(plugin != NULL && src_channels != NULL && dst_channels != NULL, return -ENXIO); if (frames == 0) return 0; #ifdef CONFIG_SND_DEBUG { unsigned int channel; for (channel = 0; channel < plugin->src_format.channels; channel++) { snd_assert(src_channels[channel].area.first % 8 == 0 && src_channels[channel].area.step % 8 == 0, return -ENXIO); snd_assert(dst_channels[channel].area.first % 8 == 0 && dst_channels[channel].area.step % 8 == 0, return -ENXIO); } } #endif data = (struct mulaw_priv *)plugin->extra_data; data->func(plugin, src_channels, dst_channels, frames); return frames; } static void init_data(struct mulaw_priv *data, int format) { #ifdef SNDRV_LITTLE_ENDIAN data->cvt_endian = snd_pcm_format_big_endian(format) > 0; #else data->cvt_endian = snd_pcm_format_little_endian(format) > 0; #endif if (!snd_pcm_format_signed(format)) data->flip = 0x8000; data->native_bytes = snd_pcm_format_physical_width(format) / 8; data->copy_bytes = data->native_bytes < 2 ? 1 : 2; if (snd_pcm_format_little_endian(format)) { data->native_ofs = data->native_bytes - data->copy_bytes; data->copy_ofs = 2 - data->copy_bytes; } else { /* S24 in 4bytes need an 1 byte offset */ data->native_ofs = data->native_bytes - snd_pcm_format_width(format) / 8; } } int snd_pcm_plugin_build_mulaw(struct snd_pcm_substream *plug, struct snd_pcm_plugin_format *src_format, struct snd_pcm_plugin_format *dst_format, struct snd_pcm_plugin **r_plugin) { int err; struct mulaw_priv *data; struct snd_pcm_plugin *plugin; struct snd_pcm_plugin_format *format; mulaw_f func; snd_assert(r_plugin != NULL, return -ENXIO); *r_plugin = NULL; snd_assert(src_format->rate == dst_format->rate, return -ENXIO); snd_assert(src_format->channels == dst_format->channels, return -ENXIO); if (dst_format->format == SNDRV_PCM_FORMAT_MU_LAW) { format = src_format; func = mulaw_encode; } else if (src_format->format == SNDRV_PCM_FORMAT_MU_LAW) { format = dst_format; func = mulaw_decode; } else { snd_BUG(); return -EINVAL; } snd_assert(snd_pcm_format_linear(format->format) != 0, return -ENXIO); err = snd_pcm_plugin_build(plug, "Mu-Law<->linear conversion", src_format, dst_format, sizeof(struct mulaw_priv), &plugin); if (err < 0) return err; data = (struct mulaw_priv *)plugin->extra_data; data->func = func; init_data(data, format->format); plugin->transfer = mulaw_transfer; *r_plugin = plugin; return 0; }