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annotate dev/s2u-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 a5200ad12d58
children
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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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15 #include <stdio.h>
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16 #include <stdlib.h>
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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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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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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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49 /* Mounting the high-nibble of the log-PCM sample */
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50 high_nibble = (0x0008) - segno;
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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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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 }