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
51 static short seg_aend[8] = {0x1F, 0x3F, 0x7F, 0xFF,
52 0x1FF, 0x3FF, 0x7FF, 0xFFF};
53 static short seg_uend[8] = {0x3F, 0x7F, 0xFF, 0x1FF,
54 0x3FF, 0x7FF, 0xFFF, 0x1FFF};
55
56 /* copy from CCITT G.711 specifications */
57 unsigned 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
78 unsigned 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
100 static short
search(short val,short * table,short size)101 search(
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
135 unsigned char
Snack_Lin2Alaw(short pcm_val)136 Snack_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 */
173 short
Snack_Alaw2Lin(unsigned char a_val)174 Snack_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 */
230 unsigned char
Snack_Lin2Mulaw(short pcm_val)231 Snack_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 */
274 short
Snack_Mulaw2Lin(unsigned char u_val)275 Snack_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 */
294 unsigned char
alaw2ulaw(unsigned char aval)295 alaw2ulaw(
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 */
304 unsigned char
ulaw2alaw(unsigned char uval)305 ulaw2alaw(
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