FreeCalypso > hg > gsm-codec-lib
annotate dev/s2a-regen.c @ 492:cc3a831712a4
libgsmhr1: implement arbitrary RTP input
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Sat, 15 Jun 2024 06:52:37 +0000 |
parents | 3afbc6c64172 |
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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 } |