1/* 2 * This source code is a product of Sun Microsystems, Inc. and is provided 3 * for unrestricted use. Users may copy or modify this source code without 4 * charge. 5 * 6 * SUN SOURCE CODE IS PROVIDED AS IS WITH NO WARRANTIES OF ANY KIND INCLUDING 7 * THE WARRANTIES OF DESIGN, MERCHANTIBILITY AND FITNESS FOR A PARTICULAR 8 * PURPOSE, OR ARISING FROM A COURSE OF DEALING, USAGE OR TRADE PRACTICE. 9 * 10 * Sun source code is provided with no support and without any obligation on 11 * the part of Sun Microsystems, Inc. to assist in its use, correction, 12 * modification or enhancement. 13 * 14 * SUN MICROSYSTEMS, INC. SHALL HAVE NO LIABILITY WITH RESPECT TO THE 15 * INFRINGEMENT OF COPYRIGHTS, TRADE SECRETS OR ANY PATENTS BY THIS SOFTWARE 16 * OR ANY PART THEREOF. 17 * 18 * In no event will Sun Microsystems, Inc. be liable for any lost revenue 19 * or profits or other special, indirect and consequential damages, even if 20 * Sun has been advised of the possibility of such damages. 21 * 22 * Sun Microsystems, Inc. 23 * 2550 Garcia Avenue 24 * Mountain View, California 94043 25 */ 26 27/* 28 * g711.c 29 * 30 * u-law, A-law and linear PCM conversions. 31 */ 32 33#include "snack.h" 34 35/* 36 * Functions Snack_Lin2Alaw, Snack_Lin2Mulaw have been updated to correctly 37 * convert unquantized 16 bit values. 38 * Tables for direct u- to A-law and A- to u-law conversions have been 39 * corrected. 40 * Borge Lindberg, Center for PersonKommunikation, Aalborg University. 41 * bli@cpk.auc.dk 42 * 43 */ 44 45#define SIGN_BIT (0x80) /* Sign bit for a A-law byte. */ 46#define QUANT_MASK (0xf) /* Quantization field mask. */ 47#define NSEGS (8) /* Number of A-law segments. */ 48#define SEG_SHIFT (4) /* Left shift for segment number. */ 49#define SEG_MASK (0x70) /* Segment field mask. */ 50 51static short seg_aend[8] = {0x1F, 0x3F, 0x7F, 0xFF, 52 0x1FF, 0x3FF, 0x7FF, 0xFFF}; 53static short seg_uend[8] = {0x3F, 0x7F, 0xFF, 0x1FF, 54 0x3FF, 0x7FF, 0xFFF, 0x1FFF}; 55 56/* copy from CCITT G.711 specifications */ 57unsigned char _u2a[128] = { /* u- to A-law conversions */ 58 1, 1, 2, 2, 3, 3, 4, 4, 59 5, 5, 6, 6, 7, 7, 8, 8, 60 9, 10, 11, 12, 13, 14, 15, 16, 61 17, 18, 19, 20, 21, 22, 23, 24, 62 25, 27, 29, 31, 33, 34, 35, 36, 63 37, 38, 39, 40, 41, 42, 43, 44, 64 46, 48, 49, 50, 51, 52, 53, 54, 65 55, 56, 57, 58, 59, 60, 61, 62, 66 64, 65, 66, 67, 68, 69, 70, 71, 67 72, 73, 74, 75, 76, 77, 78, 79, 68/* corrected: 69 81, 82, 83, 84, 85, 86, 87, 88, 70 should be: */ 71 80, 82, 83, 84, 85, 86, 87, 88, 72 89, 90, 91, 92, 93, 94, 95, 96, 73 97, 98, 99, 100, 101, 102, 103, 104, 74 105, 106, 107, 108, 109, 110, 111, 112, 75 113, 114, 115, 116, 117, 118, 119, 120, 76 121, 122, 123, 124, 125, 126, 127, 128}; 77 78unsigned char _a2u[128] = { /* A- to u-law conversions */ 79 1, 3, 5, 7, 9, 11, 13, 15, 80 16, 17, 18, 19, 20, 21, 22, 23, 81 24, 25, 26, 27, 28, 29, 30, 31, 82 32, 32, 33, 33, 34, 34, 35, 35, 83 36, 37, 38, 39, 40, 41, 42, 43, 84 44, 45, 46, 47, 48, 48, 49, 49, 85 50, 51, 52, 53, 54, 55, 56, 57, 86 58, 59, 60, 61, 62, 63, 64, 64, 87 65, 66, 67, 68, 69, 70, 71, 72, 88/* corrected: 89 73, 74, 75, 76, 77, 78, 79, 79, 90 should be: */ 91 73, 74, 75, 76, 77, 78, 79, 80, 92 93 80, 81, 82, 83, 84, 85, 86, 87, 94 88, 89, 90, 91, 92, 93, 94, 95, 95 96, 97, 98, 99, 100, 101, 102, 103, 96 104, 105, 106, 107, 108, 109, 110, 111, 97 112, 113, 114, 115, 116, 117, 118, 119, 98 120, 121, 122, 123, 124, 125, 126, 127}; 99 100static short 101search( 102 short val, 103 short *table, 104 short size) 105{ 106 short i; 107 108 for (i = 0; i < size; i++) { 109 if (val <= *table++) 110 return (i); 111 } 112 return (size); 113} 114 115/* 116 * Snack_Lin2Alaw() - Convert a 16-bit linear PCM value to 8-bit A-law 117 * 118 * Snack_Lin2Alaw() accepts an 16-bit integer and encodes it as A-law data. 119 * 120 * Linear Input Code Compressed Code 121 * ------------------------ --------------- 122 * 0000000wxyza 000wxyz 123 * 0000001wxyza 001wxyz 124 * 000001wxyzab 010wxyz 125 * 00001wxyzabc 011wxyz 126 * 0001wxyzabcd 100wxyz 127 * 001wxyzabcde 101wxyz 128 * 01wxyzabcdef 110wxyz 129 * 1wxyzabcdefg 111wxyz 130 * 131 * For further information see John C. Bellamy's Digital Telephony, 1982, 132 * John Wiley & Sons, pps 98-111 and 472-476. 133 */ 134 135unsigned char 136Snack_Lin2Alaw( 137 short pcm_val) /* 2's complement (16-bit range) */ 138{ 139 short mask; 140 short seg; 141 unsigned char aval; 142 143 pcm_val = pcm_val >> 3; 144 145 if (pcm_val >= 0) { 146 mask = 0xD5; /* sign (7th) bit = 1 */ 147 } else { 148 mask = 0x55; /* sign bit = 0 */ 149 pcm_val = -pcm_val - 1; 150 } 151 152 /* Convert the scaled magnitude to segment number. */ 153 seg = search(pcm_val, seg_aend, 8); 154 155 /* Combine the sign, segment, and quantization bits. */ 156 157 if (seg >= 8) /* out of range, return maximum value. */ 158 return (unsigned char) (0x7F ^ mask); 159 else { 160 aval = (unsigned char) seg << SEG_SHIFT; 161 if (seg < 2) 162 aval |= (pcm_val >> 1) & QUANT_MASK; 163 else 164 aval |= (pcm_val >> seg) & QUANT_MASK; 165 return (aval ^ mask); 166 } 167} 168 169/* 170 * Snack_Alaw2Lin() - Convert an A-law value to 16-bit linear PCM 171 * 172 */ 173short 174Snack_Alaw2Lin( 175 unsigned char a_val) 176{ 177 short t; 178 short seg; 179 180 a_val ^= 0x55; 181 182 t = (a_val & QUANT_MASK) << 4; 183 seg = ((unsigned)a_val & SEG_MASK) >> SEG_SHIFT; 184 switch (seg) { 185 case 0: 186 t += 8; 187 break; 188 case 1: 189 t += 0x108; 190 break; 191 default: 192 t += 0x108; 193 t <<= seg - 1; 194 } 195 return ((a_val & SIGN_BIT) ? t : -t); 196} 197 198#define BIAS (0x84) /* Bias for linear code. */ 199#define CLIP 8159 200 201/* 202 * Snack_Lin2Mulaw() - Convert a linear PCM value to u-law 203 * 204 * In order to simplify the encoding process, the original linear magnitude 205 * is biased by adding 33 which shifts the encoding range from (0 - 8158) to 206 * (33 - 8191). The result can be seen in the following encoding table: 207 * 208 * Biased Linear Input Code Compressed Code 209 * ------------------------ --------------- 210 * 00000001wxyza 000wxyz 211 * 0000001wxyzab 001wxyz 212 * 000001wxyzabc 010wxyz 213 * 00001wxyzabcd 011wxyz 214 * 0001wxyzabcde 100wxyz 215 * 001wxyzabcdef 101wxyz 216 * 01wxyzabcdefg 110wxyz 217 * 1wxyzabcdefgh 111wxyz 218 * 219 * Each biased linear code has a leading 1 which identifies the segment 220 * number. The value of the segment number is equal to 7 minus the number 221 * of leading 0's. The quantization interval is directly available as the 222 * four bits wxyz. * The trailing bits (a - h) are ignored. 223 * 224 * Ordinarily the complement of the resulting code word is used for 225 * transmission, and so the code word is complemented before it is returned. 226 * 227 * For further information see John C. Bellamy's Digital Telephony, 1982, 228 * John Wiley & Sons, pps 98-111 and 472-476. 229 */ 230unsigned char 231Snack_Lin2Mulaw( 232 short pcm_val) /* 2's complement (16-bit range) */ 233{ 234 short mask; 235 short seg; 236 unsigned char uval; 237 238 /* Get the sign and the magnitude of the value. */ 239 pcm_val = pcm_val >> 2; 240 if (pcm_val < 0) { 241 pcm_val = -pcm_val; 242 mask = 0x7F; 243 } else { 244 mask = 0xFF; 245 } 246 if ( pcm_val > CLIP ) pcm_val = CLIP; /* clip the magnitude */ 247 pcm_val += (BIAS >> 2); 248 249 /* Convert the scaled magnitude to segment number. */ 250 seg = search(pcm_val, seg_uend, 8); 251 252 /* 253 * Combine the sign, segment, quantization bits; 254 * and complement the code word. 255 */ 256 if (seg >= 8) /* out of range, return maximum value. */ 257 return (unsigned char) (0x7F ^ mask); 258 else { 259 uval = (unsigned char) (seg << 4) | ((pcm_val >> (seg + 1)) & 0xF); 260 return (uval ^ mask); 261 } 262 263} 264 265/* 266 * Snack_Mulaw2Lin() - Convert a u-law value to 16-bit linear PCM 267 * 268 * First, a biased linear code is derived from the code word. An unbiased 269 * output can then be obtained by subtracting 33 from the biased code. 270 * 271 * Note that this function expects to be passed the complement of the 272 * original code word. This is in keeping with ISDN conventions. 273 */ 274short 275Snack_Mulaw2Lin( 276 unsigned char u_val) 277{ 278 short t; 279 280 /* Complement to obtain normal u-law value. */ 281 u_val = ~u_val; 282 283 /* 284 * Extract and bias the quantization bits. Then 285 * shift up by the segment number and subtract out the bias. 286 */ 287 t = ((u_val & QUANT_MASK) << 3) + BIAS; 288 t <<= ((unsigned)u_val & SEG_MASK) >> SEG_SHIFT; 289 290 return ((u_val & SIGN_BIT) ? (BIAS - t) : (t - BIAS)); 291} 292 293/* A-law to u-law conversion */ 294unsigned char 295alaw2ulaw( 296 unsigned char aval) 297{ 298 aval &= 0xff; 299 return (unsigned char) ((aval & 0x80) ? (0xFF ^ _a2u[aval ^ 0xD5]) : 300 (0x7F ^ _a2u[aval ^ 0x55])); 301} 302 303/* u-law to A-law conversion */ 304unsigned char 305ulaw2alaw( 306 unsigned char uval) 307{ 308 uval &= 0xff; 309 return (unsigned char) ((uval & 0x80) ? (0xD5 ^ (_u2a[0xFF ^ uval] - 1)) : 310 (unsigned char) (0x55 ^ (_u2a[0x7F ^ uval] - 1))); 311} 312 313