302 lines
8.2 KiB
C
302 lines
8.2 KiB
C
/*
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* This source code is a product of Sun Microsystems, Inc. and is provided
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* for unrestricted use. Users may copy or modify this source code without
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* charge.
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*
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* SUN SOURCE CODE IS PROVIDED AS IS WITH NO WARRANTIES OF ANY KIND INCLUDING
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* THE WARRANTIES OF DESIGN, MERCHANTIBILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE, OR ARISING FROM A COURSE OF DEALING, USAGE OR TRADE PRACTICE.
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*
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* Sun source code is provided with no support and without any obligation on
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* the part of Sun Microsystems, Inc. to assist in its use, correction,
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* modification or enhancement.
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*
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* SUN MICROSYSTEMS, INC. SHALL HAVE NO LIABILITY WITH RESPECT TO THE
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* INFRINGEMENT OF COPYRIGHTS, TRADE SECRETS OR ANY PATENTS BY THIS SOFTWARE
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* OR ANY PART THEREOF.
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*
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* In no event will Sun Microsystems, Inc. be liable for any lost revenue
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* or profits or other special, indirect and consequential damages, even if
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* Sun has been advised of the possibility of such damages.
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*
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* Sun Microsystems, Inc.
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* 2550 Garcia Avenue
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* Mountain View, California 94043
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*/
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/*
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* December 30, 1994:
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* Functions linear2alaw, linear2ulaw have been updated to correctly
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* convert unquantized 16 bit values.
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* Tables for direct u- to A-law and A- to u-law conversions have been
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* corrected.
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* Borge Lindberg, Center for PersonKommunikation, Aalborg University.
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* bli@cpk.auc.dk
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*
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*/
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/*
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* Downloaded from comp.speech site in Cambridge.
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*
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*/
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#include "g711.h"
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/*
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* g711.c
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*
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* u-law, A-law and linear PCM conversions.
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*/
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#define SIGN_BIT (0x80) /* Sign bit for a A-law byte. */
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#define QUANT_MASK (0xf) /* Quantization field mask. */
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#define NSEGS (8) /* Number of A-law segments. */
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#define SEG_SHIFT (4) /* Left shift for segment number. */
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#define SEG_MASK (0x70) /* Segment field mask. */
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static short seg_aend[8] = { 0x1F, 0x3F, 0x7F, 0xFF,
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0x1FF, 0x3FF, 0x7FF, 0xFFF
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};
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static short seg_uend[8] = { 0x3F, 0x7F, 0xFF, 0x1FF,
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0x3FF, 0x7FF, 0xFFF, 0x1FFF
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};
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/* copy from CCITT G.711 specifications */
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unsigned char _u2a[128] = { /* u- to A-law conversions */
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1, 1, 2, 2, 3, 3, 4, 4,
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5, 5, 6, 6, 7, 7, 8, 8,
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9, 10, 11, 12, 13, 14, 15, 16,
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17, 18, 19, 20, 21, 22, 23, 24,
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25, 27, 29, 31, 33, 34, 35, 36,
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37, 38, 39, 40, 41, 42, 43, 44,
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46, 48, 49, 50, 51, 52, 53, 54,
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55, 56, 57, 58, 59, 60, 61, 62,
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64, 65, 66, 67, 68, 69, 70, 71,
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72, 73, 74, 75, 76, 77, 78, 79,
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/* corrected:
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81, 82, 83, 84, 85, 86, 87, 88,
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should be: */
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80, 82, 83, 84, 85, 86, 87, 88,
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89, 90, 91, 92, 93, 94, 95, 96,
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97, 98, 99, 100, 101, 102, 103, 104,
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105, 106, 107, 108, 109, 110, 111, 112,
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113, 114, 115, 116, 117, 118, 119, 120,
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121, 122, 123, 124, 125, 126, 127, 128
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};
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unsigned char _a2u[128] = { /* A- to u-law conversions */
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1, 3, 5, 7, 9, 11, 13, 15,
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16, 17, 18, 19, 20, 21, 22, 23,
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24, 25, 26, 27, 28, 29, 30, 31,
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32, 32, 33, 33, 34, 34, 35, 35,
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36, 37, 38, 39, 40, 41, 42, 43,
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44, 45, 46, 47, 48, 48, 49, 49,
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50, 51, 52, 53, 54, 55, 56, 57,
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58, 59, 60, 61, 62, 63, 64, 64,
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65, 66, 67, 68, 69, 70, 71, 72,
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/* corrected:
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73, 74, 75, 76, 77, 78, 79, 79,
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should be: */
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73, 74, 75, 76, 77, 78, 79, 80,
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80, 81, 82, 83, 84, 85, 86, 87,
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88, 89, 90, 91, 92, 93, 94, 95,
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96, 97, 98, 99, 100, 101, 102, 103,
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104, 105, 106, 107, 108, 109, 110, 111,
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112, 113, 114, 115, 116, 117, 118, 119,
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120, 121, 122, 123, 124, 125, 126, 127
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};
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static short search(short val, short *table, short size)
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{
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short i;
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for (i = 0; i < size; i++) {
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if (val <= *table++)
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return (i);
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}
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return (size);
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}
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/*
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* linear2alaw() - Convert a 16-bit linear PCM value to 8-bit A-law
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*
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* linear2alaw() accepts an 16-bit integer and encodes it as A-law data.
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*
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* Linear Input Code Compressed Code
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* ------------------------ ---------------
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* 0000000wxyza 000wxyz
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* 0000001wxyza 001wxyz
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* 000001wxyzab 010wxyz
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* 00001wxyzabc 011wxyz
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* 0001wxyzabcd 100wxyz
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* 001wxyzabcde 101wxyz
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* 01wxyzabcdef 110wxyz
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* 1wxyzabcdefg 111wxyz
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*
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* For further information see John C. Bellamy's Digital Telephony, 1982,
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* John Wiley & Sons, pps 98-111 and 472-476.
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*/
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unsigned char linear2alaw(short pcm_val)
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{ /* 2's complement (16-bit range) */
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short mask;
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short seg;
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unsigned char aval;
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pcm_val = pcm_val >> 3;
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if (pcm_val >= 0) {
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mask = 0xD5; /* sign (7th) bit = 1 */
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} else {
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mask = 0x55; /* sign bit = 0 */
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pcm_val = -pcm_val - 1;
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}
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/* Convert the scaled magnitude to segment number. */
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seg = search(pcm_val, seg_aend, 8);
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/* Combine the sign, segment, and quantization bits. */
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if (seg >= 8) /* out of range, return maximum value. */
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return (unsigned char) (0x7F ^ mask);
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else {
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aval = (unsigned char) seg << SEG_SHIFT;
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if (seg < 2)
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aval |= (pcm_val >> 1) & QUANT_MASK;
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else
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aval |= (pcm_val >> seg) & QUANT_MASK;
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return (aval ^ mask);
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}
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}
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/*
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* alaw2linear() - Convert an A-law value to 16-bit linear PCM
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*
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*/
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short alaw2linear(unsigned char a_val)
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{
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short t;
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short seg;
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a_val ^= 0x55;
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t = (a_val & QUANT_MASK) << 4;
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seg = ((unsigned) a_val & SEG_MASK) >> SEG_SHIFT;
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switch (seg) {
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case 0:
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t += 8;
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break;
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case 1:
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t += 0x108;
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break;
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default:
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t += 0x108;
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t <<= seg - 1;
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}
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return ((a_val & SIGN_BIT) ? t : -t);
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}
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#define BIAS (0x84) /* Bias for linear code. */
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#define CLIP 8159
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/*
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* linear2ulaw() - Convert a linear PCM value to u-law
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*
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* In order to simplify the encoding process, the original linear magnitude
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* is biased by adding 33 which shifts the encoding range from (0 - 8158) to
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* (33 - 8191). The result can be seen in the following encoding table:
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*
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* Biased Linear Input Code Compressed Code
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* ------------------------ ---------------
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* 00000001wxyza 000wxyz
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* 0000001wxyzab 001wxyz
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* 000001wxyzabc 010wxyz
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* 00001wxyzabcd 011wxyz
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* 0001wxyzabcde 100wxyz
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* 001wxyzabcdef 101wxyz
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* 01wxyzabcdefg 110wxyz
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* 1wxyzabcdefgh 111wxyz
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*
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* Each biased linear code has a leading 1 which identifies the segment
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* number. The value of the segment number is equal to 7 minus the number
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* of leading 0's. The quantization interval is directly available as the
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* four bits wxyz. * The trailing bits (a - h) are ignored.
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*
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* Ordinarily the complement of the resulting code word is used for
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* transmission, and so the code word is complemented before it is returned.
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*
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* For further information see John C. Bellamy's Digital Telephony, 1982,
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* John Wiley & Sons, pps 98-111 and 472-476.
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*/
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unsigned char linear2ulaw(short pcm_val)
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{ /* 2's complement (16-bit range) */
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short mask;
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short seg;
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unsigned char uval;
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/* Get the sign and the magnitude of the value. */
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pcm_val = pcm_val >> 2;
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if (pcm_val < 0) {
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pcm_val = -pcm_val;
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mask = 0x7F;
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} else {
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mask = 0xFF;
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}
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if (pcm_val > CLIP)
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pcm_val = CLIP; /* clip the magnitude */
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pcm_val += (BIAS >> 2);
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/* Convert the scaled magnitude to segment number. */
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seg = search(pcm_val, seg_uend, 8);
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/*
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* Combine the sign, segment, quantization bits;
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* and complement the code word.
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*/
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if (seg >= 8) /* out of range, return maximum value. */
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return (unsigned char) (0x7F ^ mask);
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else {
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uval = (unsigned char) (seg << 4) | ((pcm_val >> (seg + 1)) & 0xF);
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return (uval ^ mask);
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}
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}
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/*
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* ulaw2linear() - Convert a u-law value to 16-bit linear PCM
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*
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* First, a biased linear code is derived from the code word. An unbiased
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* output can then be obtained by subtracting 33 from the biased code.
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*
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* Note that this function expects to be passed the complement of the
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* original code word. This is in keeping with ISDN conventions.
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*/
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short ulaw2linear(unsigned char u_val)
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{
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short t;
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/* Complement to obtain normal u-law value. */
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u_val = ~u_val;
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/*
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* Extract and bias the quantization bits. Then
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* shift up by the segment number and subtract out the bias.
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*/
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t = ((u_val & QUANT_MASK) << 3) + BIAS;
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t <<= ((unsigned) u_val & SEG_MASK) >> SEG_SHIFT;
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return ((u_val & SIGN_BIT) ? (BIAS - t) : (t - BIAS));
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}
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/* A-law to u-law conversion */
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unsigned char alaw2ulaw(unsigned char aval)
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{
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aval &= 0xff;
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return (unsigned char) ((aval & 0x80) ? (0xFF ^ _a2u[aval ^ 0xD5]) : (0x7F ^ _a2u[aval ^ 0x55]));
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}
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/* u-law to A-law conversion */
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unsigned char ulaw2alaw(unsigned char uval)
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{
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uval &= 0xff;
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return (unsigned char) ((uval & 0x80) ? (0xD5 ^ (_u2a[0xFF ^ uval] - 1)) : (0x55 ^ (_u2a[0x7F ^ uval] - 1)));
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}
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/* ---------- end of g711.c ----------------------------------------------------- */
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