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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 #define SIGN_BIT (0x80) /* Sign bit for a A-law byte. */
33 #define QUANT_MASK (0xf) /* Quantization field mask. */
34 #define NSEGS (8) /* Number of A-law segments. */
35 #define SEG_SHIFT (4) /* Left shift for segment number. */
36 #define SEG_MASK (0x70) /* Segment field mask. */
37
38 static short seg_end[8] = {0xFF, 0x1FF, 0x3FF, 0x7FF,
39 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF};
40
41 /* copy from CCITT G.711 specifications */
42 unsigned char _u2a[128] = { /* u- to A-law conversions */
43 1, 1, 2, 2, 3, 3, 4, 4,
44 5, 5, 6, 6, 7, 7, 8, 8,
45 9, 10, 11, 12, 13, 14, 15, 16,
46 17, 18, 19, 20, 21, 22, 23, 24,
47 25, 27, 29, 31, 33, 34, 35, 36,
48 37, 38, 39, 40, 41, 42, 43, 44,
49 46, 48, 49, 50, 51, 52, 53, 54,
50 55, 56, 57, 58, 59, 60, 61, 62,
51 64, 65, 66, 67, 68, 69, 70, 71,
52 72, 73, 74, 75, 76, 77, 78, 79,
53 81, 82, 83, 84, 85, 86, 87, 88,
54 89, 90, 91, 92, 93, 94, 95, 96,
55 97, 98, 99, 100, 101, 102, 103, 104,
56 105, 106, 107, 108, 109, 110, 111, 112,
57 113, 114, 115, 116, 117, 118, 119, 120,
58 121, 122, 123, 124, 125, 126, 127, 128};
59
60 unsigned char _a2u[128] = { /* A- to u-law conversions */
61 1, 3, 5, 7, 9, 11, 13, 15,
62 16, 17, 18, 19, 20, 21, 22, 23,
63 24, 25, 26, 27, 28, 29, 30, 31,
64 32, 32, 33, 33, 34, 34, 35, 35,
65 36, 37, 38, 39, 40, 41, 42, 43,
66 44, 45, 46, 47, 48, 48, 49, 49,
67 50, 51, 52, 53, 54, 55, 56, 57,
68 58, 59, 60, 61, 62, 63, 64, 64,
69 65, 66, 67, 68, 69, 70, 71, 72,
70 73, 74, 75, 76, 77, 78, 79, 79,
71 80, 81, 82, 83, 84, 85, 86, 87,
72 88, 89, 90, 91, 92, 93, 94, 95,
73 96, 97, 98, 99, 100, 101, 102, 103,
74 104, 105, 106, 107, 108, 109, 110, 111,
75 112, 113, 114, 115, 116, 117, 118, 119,
76 120, 121, 122, 123, 124, 125, 126, 127};
77
78 static int
79 search(
80 int val,
81 short *table,
82 int size)
83 {
84 int i;
85
86 for (i = 0; i < size; i++) {
87 if (val <= *table++)
88 return (i);
89 }
90 return (size);
91 }
92
93 /*
94 * linear2alaw() - Convert a 16-bit linear PCM value to 8-bit A-law
95 *
96 * linear2alaw() accepts an 16-bit integer and encodes it as A-law data.
97 *
98 * Linear Input Code Compressed Code
99 * ------------------------ ---------------
100 * 0000000wxyza 000wxyz
101 * 0000001wxyza 001wxyz
102 * 000001wxyzab 010wxyz
103 * 00001wxyzabc 011wxyz
104 * 0001wxyzabcd 100wxyz
105 * 001wxyzabcde 101wxyz
106 * 01wxyzabcdef 110wxyz
107 * 1wxyzabcdefg 111wxyz
108 *
109 * For further information see John C. Bellamy's Digital Telephony, 1982,
110 * John Wiley & Sons, pps 98-111 and 472-476.
111 */
112 unsigned char
113 linear2alaw(
114 int pcm_val) /* 2's complement (16-bit range) */
115 {
116 int mask;
117 int seg;
118 unsigned char aval;
119
120 if (pcm_val >= 0) {
121 mask = 0xD5; /* sign (7th) bit = 1 */
122 } else {
123 mask = 0x55; /* sign bit = 0 */
124 pcm_val = -pcm_val - 8;
125 }
126
127 /* Convert the scaled magnitude to segment number. */
128 seg = search(pcm_val, seg_end, 8);
129
130 /* Combine the sign, segment, and quantization bits. */
131
132 if (seg >= 8) /* out of range, return maximum value. */
133 return (0x7F ^ mask);
134 else {
135 aval = seg << SEG_SHIFT;
136 if (seg < 2)
137 aval |= (pcm_val >> 4) & QUANT_MASK;
138 else
139 aval |= (pcm_val >> (seg + 3)) & QUANT_MASK;
140 return (aval ^ mask);
141 }
142 }
143
144 /*
145 * alaw2linear() - Convert an A-law value to 16-bit linear PCM
146 *
147 */
148 int
149 alaw2linear(
150 unsigned char a_val)
151 {
152 int t;
153 int seg;
154
155 a_val ^= 0x55;
156
157 t = (a_val & QUANT_MASK) << 4;
158 seg = ((unsigned)a_val & SEG_MASK) >> SEG_SHIFT;
159 switch (seg) {
160 case 0:
161 t += 8;
162 break;
163 case 1:
164 t += 0x108;
165 break;
166 default:
167 t += 0x108;
168 t <<= seg - 1;
169 }
170 return ((a_val & SIGN_BIT) ? t : -t);
171 }
172
173 #define BIAS (0x84) /* Bias for linear code. */
174
175 /*
176 * linear2ulaw() - Convert a linear PCM value to u-law
177 *
178 * In order to simplify the encoding process, the original linear magnitude
179 * is biased by adding 33 which shifts the encoding range from (0 - 8158) to
180 * (33 - 8191). The result can be seen in the following encoding table:
181 *
182 * Biased Linear Input Code Compressed Code
183 * ------------------------ ---------------
184 * 00000001wxyza 000wxyz
185 * 0000001wxyzab 001wxyz
186 * 000001wxyzabc 010wxyz
187 * 00001wxyzabcd 011wxyz
188 * 0001wxyzabcde 100wxyz
189 * 001wxyzabcdef 101wxyz
190 * 01wxyzabcdefg 110wxyz
191 * 1wxyzabcdefgh 111wxyz
192 *
193 * Each biased linear code has a leading 1 which identifies the segment
194 * number. The value of the segment number is equal to 7 minus the number
195 * of leading 0's. The quantization interval is directly available as the
196 * four bits wxyz. * The trailing bits (a - h) are ignored.
197 *
198 * Ordinarily the complement of the resulting code word is used for
199 * transmission, and so the code word is complemented before it is returned.
200 *
201 * For further information see John C. Bellamy's Digital Telephony, 1982,
202 * John Wiley & Sons, pps 98-111 and 472-476.
203 */
204 unsigned char
205 linear2ulaw(
206 int pcm_val) /* 2's complement (16-bit range) */
207 {
208 int mask;
209 int seg;
210 unsigned char uval;
211
212 /* Get the sign and the magnitude of the value. */
213 if (pcm_val < 0) {
214 pcm_val = BIAS - pcm_val;
215 mask = 0x7F;
216 } else {
217 pcm_val += BIAS;
218 mask = 0xFF;
219 }
220
221 /* Convert the scaled magnitude to segment number. */
222 seg = search(pcm_val, seg_end, 8);
223
224 /*
225 * Combine the sign, segment, quantization bits;
226 * and complement the code word.
227 */
228 if (seg >= 8) /* out of range, return maximum value. */
229 return (0x7F ^ mask);
230 else {
231 uval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0xF);
232 return (uval ^ mask);
233 }
234
235 }
236
237 /*
238 * ulaw2linear() - Convert a u-law value to 16-bit linear PCM
239 *
240 * First, a biased linear code is derived from the code word. An unbiased
241 * output can then be obtained by subtracting 33 from the biased code.
242 *
243 * Note that this function expects to be passed the complement of the
244 * original code word. This is in keeping with ISDN conventions.
245 */
246 int
247 ulaw2linear(
248 unsigned char u_val)
249 {
250 int t;
251
252 /* Complement to obtain normal u-law value. */
253 u_val = ~u_val;
254
255 /*
256 * Extract and bias the quantization bits. Then
257 * shift up by the segment number and subtract out the bias.
258 */
259 t = ((u_val & QUANT_MASK) << 3) + BIAS;
260 t <<= ((unsigned)u_val & SEG_MASK) >> SEG_SHIFT;
261
262 return ((u_val & SIGN_BIT) ? (BIAS - t) : (t - BIAS));
263 }
264
265 /* A-law to u-law conversion */
266 unsigned char
267 alaw2ulaw(
268 unsigned char aval)
269 {
270 aval &= 0xff;
271 return ((aval & 0x80) ? (0xFF ^ _a2u[aval ^ 0xD5]) :
272 (0x7F ^ _a2u[aval ^ 0x55]));
273 }
274
275 /* u-law to A-law conversion */
276 unsigned char
277 ulaw2alaw(
278 unsigned char uval)
279 {
280 uval &= 0xff;
281 return ((uval & 0x80) ? (0xD5 ^ (_u2a[0xFF ^ uval] - 1)) :
282 (0x55 ^ (_u2a[0x7F ^ uval] - 1)));
283 }