122 lines
4.0 KiB
C
122 lines
4.0 KiB
C
#include "alaw.h"
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signed char lin2alaw[65536]; // 16bit unsigned index
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signed char *slin2alaw; // 16bit signed index
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uint16_t alaw2lin[256]; // alaw -> 16bit PCM, Mono, 8000 hz
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// alaw -> signed 16-bit
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static short alaw_to_lin[] = {
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0x13fc, 0xec04, 0x0144, 0xfebc, 0x517c, 0xae84, 0x051c, 0xfae4,
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0x0a3c, 0xf5c4, 0x0048, 0xffb8, 0x287c, 0xd784, 0x028c, 0xfd74,
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0x1bfc, 0xe404, 0x01cc, 0xfe34, 0x717c, 0x8e84, 0x071c, 0xf8e4,
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0x0e3c, 0xf1c4, 0x00c4, 0xff3c, 0x387c, 0xc784, 0x039c, 0xfc64,
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0x0ffc, 0xf004, 0x0104, 0xfefc, 0x417c, 0xbe84, 0x041c, 0xfbe4,
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0x083c, 0xf7c4, 0x0008, 0xfff8, 0x207c, 0xdf84, 0x020c, 0xfdf4,
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0x17fc, 0xe804, 0x018c, 0xfe74, 0x617c, 0x9e84, 0x061c, 0xf9e4,
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0x0c3c, 0xf3c4, 0x0084, 0xff7c, 0x307c, 0xcf84, 0x030c, 0xfcf4,
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0x15fc, 0xea04, 0x0164, 0xfe9c, 0x597c, 0xa684, 0x059c, 0xfa64,
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0x0b3c, 0xf4c4, 0x0068, 0xff98, 0x2c7c, 0xd384, 0x02cc, 0xfd34,
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0x1dfc, 0xe204, 0x01ec, 0xfe14, 0x797c, 0x8684, 0x07bc, 0xf844,
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0x0f3c, 0xf0c4, 0x00e4, 0xff1c, 0x3c7c, 0xc384, 0x03dc, 0xfc24,
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0x11fc, 0xee04, 0x0124, 0xfedc, 0x497c, 0xb684, 0x049c, 0xfb64,
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0x093c, 0xf6c4, 0x0028, 0xffd8, 0x247c, 0xdb84, 0x024c, 0xfdb4,
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0x19fc, 0xe604, 0x01ac, 0xfe54, 0x697c, 0x9684, 0x069c, 0xf964,
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0x0d3c, 0xf2c4, 0x00a4, 0xff5c, 0x347c, 0xcb84, 0x034c, 0xfcb4,
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0x12fc, 0xed04, 0x0134, 0xfecc, 0x4d7c, 0xb284, 0x04dc, 0xfb24,
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0x09bc, 0xf644, 0x0038, 0xffc8, 0x267c, 0xd984, 0x026c, 0xfd94,
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0x1afc, 0xe504, 0x01ac, 0xfe54, 0x6d7c, 0x9284, 0x06dc, 0xf924,
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0x0dbc, 0xf244, 0x00b4, 0xff4c, 0x367c, 0xc984, 0x036c, 0xfc94,
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0x0f3c, 0xf0c4, 0x00f4, 0xff0c, 0x3e7c, 0xc184, 0x03dc, 0xfc24,
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0x07bc, 0xf844, 0x0008, 0xfff8, 0x1efc, 0xe104, 0x01ec, 0xfe14,
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0x16fc, 0xe904, 0x0174, 0xfe8c, 0x5d7c, 0xa284, 0x05dc, 0xfa24,
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0x0bbc, 0xf444, 0x0078, 0xff88, 0x2e7c, 0xd184, 0x02ec, 0xfd14,
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0x14fc, 0xeb04, 0x0154, 0xfeac, 0x557c, 0xaa84, 0x055c, 0xfaa4,
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0x0abc, 0xf544, 0x0058, 0xffa8, 0x2a7c, 0xd584, 0x02ac, 0xfd54,
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0x1cfc, 0xe304, 0x01cc, 0xfe34, 0x757c, 0x8a84, 0x075c, 0xf8a4,
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0x0ebc, 0xf144, 0x00d4, 0xff2c, 0x3a7c, 0xc584, 0x039c, 0xfc64,
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0x10fc, 0xef04, 0x0114, 0xfeec, 0x457c, 0xba84, 0x045c, 0xfba4,
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0x08bc, 0xf744, 0x0018, 0xffe8, 0x227c, 0xdd84, 0x022c, 0xfdd4,
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0x18fc, 0xe704, 0x018c, 0xfe74, 0x657c, 0x9a84, 0x065c, 0xf9a4,
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0x0cbc, 0xf344, 0x0094, 0xff6c, 0x327c, 0xcd84, 0x032c, 0xfcd4
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};
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static unsigned char linear2alaw(short sample)
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{
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int best = -1;
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int i = 0;
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int diff = 0;
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int best_diff = 0;
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while (i < 256) {
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diff = alaw_to_lin[i] - sample;
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if (diff < 0)
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diff = 0 - diff;
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if (diff < best_diff || best < 0) {
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best_diff = diff;
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best = i;
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}
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i++;
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}
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return (best);
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}
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static int alaw2linear(unsigned char sample)
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{
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signed short r = 0, sign = 1;
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// Must reverse bit order.
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sample = ((sample & 0xaaaa) >> 1) | ((sample & 0x5555) << 1);
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sample = ((sample & 0xcccc) >> 2) | ((sample & 0x3333) << 2);
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sample = (sample >> 4) | (sample << 4);
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if (sample & 0x80) {
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sample ^= 0xd5; // Flip bits for positive values
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} else {
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sample ^= 0x55; // Flip bits for negative values
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sign = -1; // Remember sign
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}
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switch (sample & 0x70) {
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case 0x70: // Segment 7 (0x800..0xfff)
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r = 0x840 | ((sample & 0xf) << 7);
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break;
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case 0x60: // Segment 6 (0x400..0x7ff)
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r = 0x420 | ((sample & 0xf) << 6);
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break;
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case 0x50: // Segment 5 (0x200..0x3ff)
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r = 0x210 | ((sample & 0xf) << 5);
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break;
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case 0x40: // Segment 4 (0x100..0x1ff)
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r = 0x108 | ((sample & 0xf) << 4);
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break;
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case 0x30: // Segment 3 (0x080..0x0ff)
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r = 0x084 | ((sample & 0xf) << 3);
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break;
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case 0x20: // Segment 2 (0x040..0x07f)
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r = 0x042 | ((sample & 0xf) << 2);
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break;
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default: // Segment 1 (0x000..0x03f)
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r = 0x001 | ((sample & 0x1f) << 1);
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}
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return (r * sign) << 3;
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}
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// Build table .. makes encoding pretty fast :)
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void create_lin2alaw_table(void)
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{
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int i;
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slin2alaw = &lin2alaw[32768];
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// build law->linear16
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for (i = 0; i < 65535; i++)
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slin2alaw[i - 32768] = linear2alaw((short)i - 32768);
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// build linear16->law
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for (i = 0; i < 256; i++) {
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alaw2lin[i] = alaw2linear((unsigned char)i);
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}
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}
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