FreeCalypso > hg > gsm-codec-lib
view dev/s2u-regen.c @ 399:3618b5cf25a6
libtwamr: integrate preemph.c
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Mon, 06 May 2024 19:19:27 +0000 |
parents | a5200ad12d58 |
children |
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/* * This program generates a G.711 mu-law encoding table of the same form * as the s2u[] table in the toast_ulaw.c module in libgsm/toast, i.e., * an encoding table that takes only the upper 13 bits of the linear PCM * sample to be encoded, even though canonical mu-law encoding requires * 14-bit input. The 13-bit table constructed by this program is computed * as if the lsb of the "proper" 14-bit input is always zero, like it is * expected to be when the linear PCM samples came from the output of a * GSM speech decoder. * * The "engine" function that does the computation is based on ulaw_compress() * from ITU-T G.191 STL. */ #include <stdio.h> #include <stdlib.h> static unsigned ulaw_compress(input) unsigned input; { short i; /* aux.var. */ short absno; /* absolute value of linear (input) sample */ short segno; /* segment (Table 2/G711, column 1) */ short low_nibble; /* low nibble of log companded sample */ short high_nibble; /* high nibble of log companded sample */ unsigned output; /* -------------------------------------------------------------------- */ /* Input is 14-bit right-justified in this version */ /* Compute absolute value; adjust for easy processing */ /* -------------------------------------------------------------------- */ absno = input >= 0x2000 /* compute 1's complement in case of */ ? (~input & 0x1FFF) + 33 /* negative samples */ : input + 33; /* NB: 33 is the difference value */ /* between the thresholds for */ /* A-law and u-law. */ if (absno > (0x1FFF)) /* limitation to "absno" < 8192 */ absno = (0x1FFF); /* Determination of sample's segment */ i = absno >> 6; segno = 1; while (i != 0) { segno++; i >>= 1; } /* Mounting the high-nibble of the log-PCM sample */ high_nibble = (0x0008) - segno; /* Mounting the low-nibble of the log PCM sample */ low_nibble = (absno >> segno) /* right shift of mantissa and */ &(0x000F); /* masking away leading '1' */ low_nibble = (0x000F) - low_nibble; /* Joining the high-nibble and the low-nibble of the log PCM sample */ output = (high_nibble << 4) | low_nibble; /* Add sign bit */ if (input < 0x2000) output = output | (0x0080); return output; } main(argc, argv) char **argv; { unsigned input, output; for (input = 0; input < 8192; input++) { output = ulaw_compress(input << 1); printf("%04o,", output); if ((input % 15) == 14 || input == 8191) putchar('\n'); } exit(0); }