FreeCalypso > hg > gsm-codec-lib
annotate dev/s2u-regen.c @ 539:0daaae66b3f6
libtest: add TW-TS-005 write helper function
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Sun, 22 Sep 2024 00:21:16 +0000 |
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1 /* |
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2 * This program generates a G.711 mu-law encoding table of the same form |
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3 * as the s2u[] table in the toast_ulaw.c module in libgsm/toast, i.e., |
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4 * an encoding table that takes only the upper 13 bits of the linear PCM |
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5 * sample to be encoded, even though canonical mu-law encoding requires |
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6 * 14-bit input. The 13-bit table constructed by this program is computed |
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7 * as if the lsb of the "proper" 14-bit input is always zero, like it is |
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8 * expected to be when the linear PCM samples came from the output of a |
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9 * GSM speech decoder. |
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10 * |
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11 * The "engine" function that does the computation is based on ulaw_compress() |
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12 * from ITU-T G.191 STL. |
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13 */ |
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14 |
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15 #include <stdio.h> |
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16 #include <stdlib.h> |
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17 |
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18 static unsigned |
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19 ulaw_compress(input) |
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20 unsigned input; |
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21 { |
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22 short i; /* aux.var. */ |
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23 short absno; /* absolute value of linear (input) sample */ |
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24 short segno; /* segment (Table 2/G711, column 1) */ |
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25 short low_nibble; /* low nibble of log companded sample */ |
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26 short high_nibble; /* high nibble of log companded sample */ |
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27 unsigned output; |
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28 |
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29 /* -------------------------------------------------------------------- */ |
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30 /* Input is 14-bit right-justified in this version */ |
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31 /* Compute absolute value; adjust for easy processing */ |
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32 /* -------------------------------------------------------------------- */ |
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33 absno = input >= 0x2000 /* compute 1's complement in case of */ |
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34 ? (~input & 0x1FFF) + 33 /* negative samples */ |
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35 : input + 33; /* NB: 33 is the difference value */ |
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36 /* between the thresholds for */ |
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37 /* A-law and u-law. */ |
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38 if (absno > (0x1FFF)) /* limitation to "absno" < 8192 */ |
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39 absno = (0x1FFF); |
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40 |
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41 /* Determination of sample's segment */ |
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42 i = absno >> 6; |
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43 segno = 1; |
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44 while (i != 0) { |
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45 segno++; |
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46 i >>= 1; |
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47 } |
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48 |
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49 /* Mounting the high-nibble of the log-PCM sample */ |
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50 high_nibble = (0x0008) - segno; |
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51 |
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52 /* Mounting the low-nibble of the log PCM sample */ |
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53 low_nibble = (absno >> segno) /* right shift of mantissa and */ |
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54 &(0x000F); /* masking away leading '1' */ |
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55 low_nibble = (0x000F) - low_nibble; |
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56 |
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57 /* Joining the high-nibble and the low-nibble of the log PCM sample */ |
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58 output = (high_nibble << 4) | low_nibble; |
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59 |
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60 /* Add sign bit */ |
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61 if (input < 0x2000) |
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62 output = output | (0x0080); |
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63 |
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64 return output; |
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65 } |
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66 |
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67 main(argc, argv) |
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68 char **argv; |
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69 { |
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70 unsigned input, output; |
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71 |
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72 for (input = 0; input < 8192; input++) { |
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73 output = ulaw_compress(input << 1); |
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74 printf("%04o,", output); |
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75 if ((input % 15) == 14 || input == 8191) |
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76 putchar('\n'); |
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77 } |
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78 exit(0); |
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79 } |