FreeCalypso > hg > gsm-codec-lib

annotate dev/u2s-regen.c @ 282:9ee8ad3d4d30

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frtest: rm gsmfr-hand-test and gsmfr-max-out utils These hack programs were never properly documented and were written only as part of a debug chase, in pursuit of a bug that ultimately turned out to be in our then-hacky patch to osmo-bts-sysmo, before beginning of proper patches in Osmocom. These hack programs need to be dropped from the present sw package because they depend on old libgsm, and we are eliminating that dependency.
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 14 Apr 2024 05:44:47 +0000
parents 20750ffb1c3e
children
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1 /*
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2 * This program generates a G.711 mu-law decoding table of the same form
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3 * as the u2s[] table in the toast_ulaw.c module in libgsm/toast; the intent
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4 * is to replace that incorrect table with a corrected one. The "engine"
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5 * function that does the computation is based on ulaw_expand() from ITU-T
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6 * G.191 STL.
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7 */
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8
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9 #include <stdio.h>
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10 #include <stdlib.h>
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12 static unsigned
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13 ulaw_expand (input)
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14 unsigned input;
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15 {
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16 short segment; /* segment (Table 2/G711, column 1) */
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17 short mantissa; /* low nibble of log companded sample */
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18 short exponent; /* high nibble of log companded sample */
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19 short sign; /* sign of output sample */
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20 short step;
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21 short output;
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23 sign = input < (0x0080) /* sign-bit = 1 for positiv values */
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24 ? -1 : 1;
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25 mantissa = ~input; /* 1's complement of input value */
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26 exponent = (mantissa >> 4) & (0x0007); /* extract exponent */
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27 segment = exponent + 1; /* compute segment number */
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28 mantissa = mantissa & (0x000F); /* extract mantissa */
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30 /* Compute Quantized Sample (14 bit left justified!) */
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31 step = (4) << segment; /* position of the LSB */
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32 /* = 1 quantization step) */
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33 output = sign * /* sign */
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34 (((0x0080) << exponent) /* '1', preceding the mantissa */
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35 +step * mantissa /* left shift of mantissa */
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36 + step / 2 /* 1/2 quantization step */
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37 - 4 * 33);
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38 return output & 0xFFFF;
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39 }
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41 main(argc, argv)
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42 char **argv;
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43 {
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44 unsigned input, output;
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45
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46 for (input = 0; input < 256; input++) {
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47 output = ulaw_expand(input);
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48 printf("%6u,", output);
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49 if ((input & 7) == 7)
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50 putchar('\n');
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51 }
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52 exit(0);
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53 }