FreeCalypso > hg > gsm-codec-lib
annotate dev/u2s-regen.c @ 463:9208db14b4b9
doc/EFR-library-API: rm reference to old libgsm
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Sat, 11 May 2024 20:29:11 +0000 |
parents | 20750ffb1c3e |
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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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11 |
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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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22 |
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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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29 |
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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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40 |
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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 } |