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