Jacob Erlbeck | 239a853 | 2014-03-13 14:25:51 +0100 | [diff] [blame] | 1 | /* |
| 2 | * PCM - A-Law conversion |
| 3 | * Copyright (c) 2000 by Abramo Bagnara <abramo@alsa-project.org> |
| 4 | * |
| 5 | * Wrapper for linphone Codec class by Simon Morlat <simon.morlat@linphone.org> |
| 6 | * |
| 7 | * |
| 8 | * This program is free software; you can redistribute it and/or modify |
| 9 | * it under the terms of the GNU General Public License as published by |
| 10 | * the Free Software Foundation; either version 2 of the License, or |
| 11 | * (at your option) any later version. |
| 12 | * |
| 13 | * This program is distributed in the hope that it will be useful, |
| 14 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 16 | * GNU General Public License for more details. |
| 17 | * |
| 18 | * You should have received a copy of the GNU General Public License |
| 19 | * along with this program; if not, write to the Free Software |
| 20 | * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA |
| 21 | */ |
| 22 | |
| 23 | static inline int val_seg(int val) |
| 24 | { |
| 25 | int r = 0; |
| 26 | val >>= 7; /*7 = 4 + 3*/ |
| 27 | if (val & 0xf0) { |
| 28 | val >>= 4; |
| 29 | r += 4; |
| 30 | } |
| 31 | if (val & 0x0c) { |
| 32 | val >>= 2; |
| 33 | r += 2; |
| 34 | } |
| 35 | if (val & 0x02) |
| 36 | r += 1; |
| 37 | return r; |
| 38 | } |
| 39 | |
| 40 | /* |
| 41 | * s16_to_alaw() - Convert a 16-bit linear PCM value to 8-bit A-law |
| 42 | * |
| 43 | * s16_to_alaw() accepts an 16-bit integer and encodes it as A-law data. |
| 44 | * |
| 45 | * Linear Input Code Compressed Code |
| 46 | * ------------------------ --------------- |
| 47 | * 0000000wxyza 000wxyz |
| 48 | * 0000001wxyza 001wxyz |
| 49 | * 000001wxyzab 010wxyz |
| 50 | * 00001wxyzabc 011wxyz |
| 51 | * 0001wxyzabcd 100wxyz |
| 52 | * 001wxyzabcde 101wxyz |
| 53 | * 01wxyzabcdef 110wxyz |
| 54 | * 1wxyzabcdefg 111wxyz |
| 55 | * |
| 56 | * For further information see John C. Bellamy's Digital Telephony, 1982, |
| 57 | * John Wiley & Sons, pps 98-111 and 472-476. |
| 58 | * G711 is designed for 13 bits input signal, this function add extra shifting to take this into account. |
| 59 | */ |
| 60 | |
| 61 | static inline unsigned char s16_to_alaw(int pcm_val) |
| 62 | { |
| 63 | int mask; |
| 64 | int seg; |
| 65 | unsigned char aval; |
| 66 | |
| 67 | if (pcm_val >= 0) { |
| 68 | mask = 0xD5; |
| 69 | } else { |
| 70 | mask = 0x55; |
| 71 | pcm_val = -pcm_val; |
| 72 | if (pcm_val > 0x7fff) |
| 73 | pcm_val = 0x7fff; |
| 74 | } |
| 75 | |
| 76 | if (pcm_val < 256) /*256 = 32 << 3*/ |
| 77 | aval = pcm_val >> 4; /*4 = 1 + 3*/ |
| 78 | else { |
| 79 | /* Convert the scaled magnitude to segment number. */ |
| 80 | seg = val_seg(pcm_val); |
| 81 | aval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0x0f); |
| 82 | } |
| 83 | return aval ^ mask; |
| 84 | } |
| 85 | |
| 86 | /* |
| 87 | * alaw_to_s16() - Convert an A-law value to 16-bit linear PCM |
| 88 | * |
| 89 | */ |
| 90 | static inline int alaw_to_s16(unsigned char a_val) |
| 91 | { |
| 92 | int t; |
| 93 | int seg; |
| 94 | |
| 95 | a_val ^= 0x55; |
| 96 | t = a_val & 0x7f; |
| 97 | if (t < 16) |
| 98 | t = (t << 4) + 8; |
| 99 | else { |
| 100 | seg = (t >> 4) & 0x07; |
| 101 | t = ((t & 0x0f) << 4) + 0x108; |
| 102 | t <<= seg -1; |
| 103 | } |
| 104 | return ((a_val & 0x80) ? t : -t); |
| 105 | } |
| 106 | /* |
| 107 | * s16_to_ulaw() - Convert a linear PCM value to u-law |
| 108 | * |
| 109 | * In order to simplify the encoding process, the original linear magnitude |
| 110 | * is biased by adding 33 which shifts the encoding range from (0 - 8158) to |
| 111 | * (33 - 8191). The result can be seen in the following encoding table: |
| 112 | * |
| 113 | * Biased Linear Input Code Compressed Code |
| 114 | * ------------------------ --------------- |
| 115 | * 00000001wxyza 000wxyz |
| 116 | * 0000001wxyzab 001wxyz |
| 117 | * 000001wxyzabc 010wxyz |
| 118 | * 00001wxyzabcd 011wxyz |
| 119 | * 0001wxyzabcde 100wxyz |
| 120 | * 001wxyzabcdef 101wxyz |
| 121 | * 01wxyzabcdefg 110wxyz |
| 122 | * 1wxyzabcdefgh 111wxyz |
| 123 | * |
| 124 | * Each biased linear code has a leading 1 which identifies the segment |
| 125 | * number. The value of the segment number is equal to 7 minus the number |
| 126 | * of leading 0's. The quantization interval is directly available as the |
| 127 | * four bits wxyz. * The trailing bits (a - h) are ignored. |
| 128 | * |
| 129 | * Ordinarily the complement of the resulting code word is used for |
| 130 | * transmission, and so the code word is complemented before it is returned. |
| 131 | * |
| 132 | * For further information see John C. Bellamy's Digital Telephony, 1982, |
| 133 | * John Wiley & Sons, pps 98-111 and 472-476. |
| 134 | */ |
| 135 | |
| 136 | static inline unsigned char s16_to_ulaw(int pcm_val) /* 2's complement (16-bit range) */ |
| 137 | { |
| 138 | int mask; |
| 139 | int seg; |
| 140 | unsigned char uval; |
| 141 | |
| 142 | if (pcm_val < 0) { |
| 143 | pcm_val = 0x84 - pcm_val; |
| 144 | mask = 0x7f; |
| 145 | } else { |
| 146 | pcm_val += 0x84; |
| 147 | mask = 0xff; |
| 148 | } |
| 149 | if (pcm_val > 0x7fff) |
| 150 | pcm_val = 0x7fff; |
| 151 | |
| 152 | /* Convert the scaled magnitude to segment number. */ |
| 153 | seg = val_seg(pcm_val); |
| 154 | |
| 155 | /* |
| 156 | * Combine the sign, segment, quantization bits; |
| 157 | * and complement the code word. |
| 158 | */ |
| 159 | uval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0x0f); |
| 160 | return uval ^ mask; |
| 161 | } |
| 162 | |
| 163 | /* |
| 164 | * ulaw_to_s16() - Convert a u-law value to 16-bit linear PCM |
| 165 | * |
| 166 | * First, a biased linear code is derived from the code word. An unbiased |
| 167 | * output can then be obtained by subtracting 33 from the biased code. |
| 168 | * |
| 169 | * Note that this function expects to be passed the complement of the |
| 170 | * original code word. This is in keeping with ISDN conventions. |
| 171 | */ |
| 172 | static inline int ulaw_to_s16(unsigned char u_val) |
| 173 | { |
| 174 | int t; |
| 175 | |
| 176 | /* Complement to obtain normal u-law value. */ |
| 177 | u_val = ~u_val; |
| 178 | |
| 179 | /* |
| 180 | * Extract and bias the quantization bits. Then |
| 181 | * shift up by the segment number and subtract out the bias. |
| 182 | */ |
| 183 | t = ((u_val & 0x0f) << 3) + 0x84; |
| 184 | t <<= (u_val & 0x70) >> 4; |
| 185 | |
| 186 | return ((u_val & 0x80) ? (0x84 - t) : (t - 0x84)); |
| 187 | } |