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341 lines
8.1 KiB
JavaScript
341 lines
8.1 KiB
JavaScript
var SIGN_BIT = 0x80; /* Sign bit for a A-law byte. */
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var QUANT_MASK = 0xf; /* Quantization field mask. */
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var NSEGS = 0x8; /* Number of A-law segments. */
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var SEG_SHIFT = 0x4; /* Left shift for segment number. */
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var SEG_MASK = 0x70; /* Segment field mask. */
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var seg_aend = new Int16Array([0x1F, 0x3F, 0x7F, 0xFF,0x1FF, 0x3FF, 0x7FF, 0xFFF]);
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var seg_uend = new Int16Array([0x3F, 0x7F, 0xFF, 0x1FF,0x3FF, 0x7FF, 0xFFF, 0x1FFF]);
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/* copy from CCITT G.711 specifications */
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var _u2a = new Uint8Array([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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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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/* A- to u-law conversions */
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var _a2u = new Uint8Array([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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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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function search( val, table, size)
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{
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var i;
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for (i = 0; i < size; i++) {
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if (val <= table[i])
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return (i);
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}
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return (size);
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}
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function linear2alaw(pcm_val) /* 2's complement (16-bit range) */
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{
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var mask;
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var seg;
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var 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 (0x7F ^ mask);
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else {
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aval = 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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function alaw2linear(a_val){
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var t;
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var seg;
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a_val ^= 0x55;
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t = (a_val & QUANT_MASK) << 4;
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seg = (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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var BIAS = 0x84;
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var 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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function linear2ulaw(pcm_val) /* 2's complement (16-bit range) */
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{
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var mask;
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var seg;
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var 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 ) 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 (0x7F ^ mask);
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else {
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uval = (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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function ulaw2linear(u_val)
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{
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var 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 <<= (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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function alaw2ulaw(aval)
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{
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aval &= 0xff;
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return ((aval & 0x80) ? (0xFF ^ _a2u[aval ^ 0xD5]) :
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(0x7F ^ _a2u[aval ^ 0x55]));
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}
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/* u-law to A-law conversion */
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function ulaw2alaw(uval)
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{
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uval &= 0xff;
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return ((uval & 0x80) ? (0xD5 ^ (_u2a[0xFF ^ uval] - 1)) :
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(0x55 ^ (_u2a[0x7F ^ uval] - 1)));
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}
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// unsigned char linear_to_alaw[65536];
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// unsigned char linear_to_ulaw[65536];
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var short_index = new Int16Array(65536);
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var linear_to_alaw = new Uint8Array(65536);
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var linear_to_ulaw = new Uint8Array(65536);
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// /* 16384 entries per table (8 bit) */
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// unsigned short alaw_to_linear[256];
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// unsigned short ulaw_to_linear[256];
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var alaw_to_linear = new Uint8Array(256);
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var ulaw_to_linear = new Uint8Array(256);
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function build_linear_to_xlaw_table(linear_to_xlaw,linear2xlaw)
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{
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var i;
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for (i=0; i<65536;i++){
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var v = linear2xlaw(short_index[i]);
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linear_to_xlaw[i] = v;
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}
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}
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function build_xlaw_to_linear_table(xlaw_to_linear,xlaw2linear)
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{
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var i;
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for (i=0; i<256;i++){
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xlaw_to_linear[i] = xlaw2linear(i);
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}
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}
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function pcm16_to_xlaw(linear_to_xlaw, src_length,src_samples,dst_samples)
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{
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var i;
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var s_samples;
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s_samples = src_samples;
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for (i=0; i < src_length / 2; i++)
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{
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dst_samples[i] = linear_to_xlaw[s_samples[i]];
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}
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}
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function xlaw_to_pcm16(xlaw_to_linear, src_length,src_samples, dst_samples)
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{
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var i;
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var s_samples;
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var d_samples;
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s_samples = src_samples;
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d_samples = dst_samples;
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for (i=0; i < src_length; i++)
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{
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d_samples[i] = xlaw_to_linear[s_samples[i]];
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}
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}
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function pcm16_to_alaw(src_length, src_samples, dst_samples)
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{
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pcm16_to_xlaw(linear_to_alaw, src_length, src_samples, dst_samples);
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}
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function pcm16_to_ulaw(src_length, src_samples, dst_samples)
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{
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pcm16_to_xlaw(linear_to_ulaw, src_length, src_samples, dst_samples);
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}
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function alaw_to_pcm16(src_length, src_samples, dst_samples)
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{
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xlaw_to_pcm16(alaw_to_linear, src_length, src_samples, dst_samples);
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}
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function ulaw_to_pcm16(src_length, src_samples, dst_samples)
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{
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xlaw_to_pcm16(ulaw_to_linear, src_length, src_samples, dst_samples);
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}
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function pcm16_alaw_tableinit()
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{
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build_linear_to_xlaw_table(linear_to_alaw, linear2alaw);
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}
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function pcm16_ulaw_tableinit()
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{
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build_linear_to_xlaw_table(linear_to_ulaw, linear2ulaw);
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}
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function alaw_pcm16_tableinit()
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{
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build_xlaw_to_linear_table(alaw_to_linear, alaw2linear);
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}
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function ulaw_pcm16_tableinit()
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{
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build_xlaw_to_linear_table(ulaw_to_linear, ulaw2linear);
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}
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for(var i =0; i < 65536;i++){
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short_index[i] = i;
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}
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pcm16_alaw_tableinit();
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pcm16_ulaw_tableinit();
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alaw_pcm16_tableinit();
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ulaw_pcm16_tableinit(); |