188 lines
4.9 KiB
C
188 lines
4.9 KiB
C
/*
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* PCM - A-Law conversion
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* Copyright (c) 2000 by Abramo Bagnara <abramo@alsa-project.org>
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*
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* Wrapper for linphone Codec class by Simon Morlat <simon.morlat@linphone.org>
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*
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (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 General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; 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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static inline int val_seg(int val)
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{
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int r = 0;
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val >>= 7; /*7 = 4 + 3*/
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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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/*
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* s16_to_alaw() - Convert a 16-bit linear PCM value to 8-bit A-law
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*
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* s16_to_alaw() accepts an 16-bit integer and encodes it as A-law data.
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*
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* Linear Input Code Compressed Code
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* ------------------------ ---------------
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* 0000000wxyza 000wxyz
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* 0000001wxyza 001wxyz
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* 000001wxyzab 010wxyz
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* 00001wxyzabc 011wxyz
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* 0001wxyzabcd 100wxyz
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* 001wxyzabcde 101wxyz
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* 01wxyzabcdef 110wxyz
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* 1wxyzabcdefg 111wxyz
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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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* G711 is designed for 13 bits input signal, this function add extra shifting to take this into account.
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*/
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static inline unsigned char s16_to_alaw(int pcm_val)
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{
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int mask;
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int seg;
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unsigned char aval;
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if (pcm_val >= 0) {
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mask = 0xD5;
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} else {
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mask = 0x55;
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pcm_val = -pcm_val;
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if (pcm_val > 0x7fff)
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pcm_val = 0x7fff;
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}
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if (pcm_val < 256) /*256 = 32 << 3*/
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aval = pcm_val >> 4; /*4 = 1 + 3*/
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else {
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/* Convert the scaled magnitude to segment number. */
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seg = val_seg(pcm_val);
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aval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0x0f);
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}
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return aval ^ mask;
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}
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/*
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* alaw_to_s16() - Convert an A-law value to 16-bit linear PCM
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*
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*/
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static inline int alaw_to_s16(unsigned char a_val)
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{
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int t;
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int seg;
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a_val ^= 0x55;
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t = a_val & 0x7f;
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if (t < 16)
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t = (t << 4) + 8;
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else {
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seg = (t >> 4) & 0x07;
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t = ((t & 0x0f) << 4) + 0x108;
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t <<= seg -1;
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}
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return ((a_val & 0x80) ? t : -t);
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}
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/*
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* s16_to_ulaw() - 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 inline unsigned char s16_to_ulaw(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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if (pcm_val < 0) {
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pcm_val = 0x84 - pcm_val;
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mask = 0x7f;
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} else {
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pcm_val += 0x84;
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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)) & 0x0f);
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return uval ^ mask;
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}
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/*
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* ulaw_to_s16() - 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 inline int ulaw_to_s16(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 & 0x0f) << 3) + 0x84;
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t <<= (u_val & 0x70) >> 4;
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return ((u_val & 0x80) ? (0x84 - t) : (t - 0x84));
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}
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