FreeCalypso > hg > gsm-codec-lib

comparison dev/s2a-regen.c @ 222:842136bbd0da

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
dev: new program s2a-regen
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 23 Apr 2023 04:09:24 +0000
parents
children 3afbc6c64172
comparison
equal deleted inserted replaced
221:6555dae764b3 222:842136bbd0da
1 /*
2 * This program regenerates a G.711 A-law encoding table equivalent to the
3 * s2a[] table in the toast_alaw.c module in libgsm/toast; the intent is
4 * to check that table for correctness. The "engine" function that does
5 * the computation is based on alaw_compress() from ITU-T G.191 STL.
6 */
7
8 #include <stdio.h>
9 #include <stdlib.h>
10
11 static unsigned
12 alaw_compress (input)
13 unsigned input;
14 {
15 short ix, iexp;
16
17 ix = input >= 2048 /* 0 <= ix < 2048 */
18 ? ~input & 2047 /* 1's complement for negative values */
19 : input;
20
21 /* Do more, if exponent > 0 */
22 if (ix > 15) { /* exponent=0 for ix <= 15 */
23 iexp = 1; /* first step: */
24 while (ix > 16 + 15) { /* find mantissa and exponent */
25 ix >>= 1;
26 iexp++;
27 }
28 ix -= 16; /* second step: remove leading '1' */
29
30 ix += iexp << 4; /* now compute encoded value */
31 }
32 if (input < 2048)
33 ix |= (0x0080); /* add sign bit */
34
35 return ix ^ (0x0055); /* toggle even bits */
36 }
37
38 main(argc, argv)
39 char **argv;
40 {
41 unsigned input, output;
42
43 for (input = 0; input < 4096; input++) {
44 if ((input & 15) == 0)
45 putchar('\t');
46 output = alaw_compress(input);
47 printf("%03u,", output);
48 if ((input & 15) == 15)
49 putchar('\n');
50 }
51 exit(0);
52 }