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Diffstat (limited to 'src/libmgcp/g711common.h')
| -rw-r--r-- | src/libmgcp/g711common.h | 187 |
1 files changed, 187 insertions, 0 deletions
diff --git a/src/libmgcp/g711common.h b/src/libmgcp/g711common.h new file mode 100644 index 000000000..cb35fc651 --- /dev/null +++ b/src/libmgcp/g711common.h @@ -0,0 +1,187 @@ +/* + * PCM - A-Law conversion + * Copyright (c) 2000 by Abramo Bagnara <abramo@alsa-project.org> + * + * Wrapper for linphone Codec class by Simon Morlat <simon.morlat@linphone.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 + */ + +static inline int val_seg(int val) +{ + int r = 0; + val >>= 7; /*7 = 4 + 3*/ + if (val & 0xf0) { + val >>= 4; + r += 4; + } + if (val & 0x0c) { + val >>= 2; + r += 2; + } + if (val & 0x02) + r += 1; + return r; +} + +/* + * s16_to_alaw() - Convert a 16-bit linear PCM value to 8-bit A-law + * + * s16_to_alaw() accepts an 16-bit integer and encodes it as A-law data. + * + * Linear Input Code Compressed Code + * ------------------------ --------------- + * 0000000wxyza 000wxyz + * 0000001wxyza 001wxyz + * 000001wxyzab 010wxyz + * 00001wxyzabc 011wxyz + * 0001wxyzabcd 100wxyz + * 001wxyzabcde 101wxyz + * 01wxyzabcdef 110wxyz + * 1wxyzabcdefg 111wxyz + * + * For further information see John C. Bellamy's Digital Telephony, 1982, + * John Wiley & Sons, pps 98-111 and 472-476. + * G711 is designed for 13 bits input signal, this function add extra shifting to take this into account. + */ + +static inline unsigned char s16_to_alaw(int pcm_val) +{ + int mask; + int seg; + unsigned char aval; + + if (pcm_val >= 0) { + mask = 0xD5; + } else { + mask = 0x55; + pcm_val = -pcm_val; + if (pcm_val > 0x7fff) + pcm_val = 0x7fff; + } + + if (pcm_val < 256) /*256 = 32 << 3*/ + aval = pcm_val >> 4; /*4 = 1 + 3*/ + else { + /* Convert the scaled magnitude to segment number. */ + seg = val_seg(pcm_val); + aval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0x0f); + } + return aval ^ mask; +} + +/* + * alaw_to_s16() - Convert an A-law value to 16-bit linear PCM + * + */ +static inline int alaw_to_s16(unsigned char a_val) +{ + int t; + int seg; + + a_val ^= 0x55; + t = a_val & 0x7f; + if (t < 16) + t = (t << 4) + 8; + else { + seg = (t >> 4) & 0x07; + t = ((t & 0x0f) << 4) + 0x108; + t <<= seg -1; + } + return ((a_val & 0x80) ? t : -t); +} +/* + * s16_to_ulaw() - 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 inline unsigned char s16_to_ulaw(int pcm_val) /* 2's complement (16-bit range) */ +{ + int mask; + int seg; + unsigned char uval; + + if (pcm_val < 0) { + pcm_val = 0x84 - pcm_val; + mask = 0x7f; + } else { + pcm_val += 0x84; + 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)) & 0x0f); + return uval ^ mask; +} + +/* + * ulaw_to_s16() - 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 inline int ulaw_to_s16(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 & 0x0f) << 3) + 0x84; + t <<= (u_val & 0x70) >> 4; + + return ((u_val & 0x80) ? (0x84 - t) : (t - 0x84)); +} |