FreeCalypso > hg > gsm-codec-lib
view dev/s2a-regen.c @ 482:5e2d849a4fbc
doc/Calypso-TCH-downlink: grammar fix
author | Mychaela Falconia <falcon@freecalypso.org> |
---|---|
date | Mon, 20 May 2024 01:24:22 +0000 |
parents | 3afbc6c64172 |
children |
line wrap: on
line source
/* * This program regenerates a G.711 A-law encoding table equivalent to the * s2a[] table in the toast_alaw.c module in libgsm/toast; the intent is * to check that table for correctness. The "engine" function that does * the computation is based on alaw_compress() from ITU-T G.191 STL. */ #include <stdio.h> #include <stdlib.h> static unsigned alaw_compress (input) unsigned input; { short ix, iexp; ix = input >= 2048 /* 0 <= ix < 2048 */ ? ~input & 2047 /* 1's complement for negative values */ : input; /* Do more, if exponent > 0 */ if (ix > 15) { /* exponent=0 for ix <= 15 */ iexp = 1; /* first step: */ while (ix > 16 + 15) { /* find mantissa and exponent */ ix >>= 1; iexp++; } ix -= 16; /* second step: remove leading '1' */ ix += iexp << 4; /* now compute encoded value */ } if (input < 2048) ix |= (0x0080); /* add sign bit */ return ix ^ (0x0055); /* toggle even bits */ } main(argc, argv) char **argv; { unsigned input, output; for (input = 0; input < 4096; input++) { if ((input & 15) == 0) putchar('\t'); output = alaw_compress(input); printf("%3u,", output); if ((input & 15) == 15) putchar('\n'); } exit(0); }