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annotate dev/s2u-regen.c @ 226:84d22eb72196

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dev: new program s2u-regen
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 23 Apr 2023 05:17:06 +0000
parents dev/s2a-regen.c@3afbc6c64172
children a5200ad12d58
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1 /*
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2 * This program regenerates a G.711 mu-law encoding table equivalent to the
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3 * s2u[] table in the toast_ulaw.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 ulaw_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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11 static unsigned
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12 ulaw_compress(input)
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13 unsigned input;
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14 {
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15 short i; /* aux.var. */
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16 short absno; /* absolute value of linear (input) sample */
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17 short segno; /* segment (Table 2/G711, column 1) */
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18 short low_nibble; /* low nibble of log companded sample */
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19 short high_nibble; /* high nibble of log companded sample */
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20 unsigned output;
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21
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22 /* -------------------------------------------------------------------- */
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23 /* Change from 14 bit left justified to 14 bit right justified */
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24 /* Compute absolute value; adjust for easy processing */
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25 /* -------------------------------------------------------------------- */
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26 absno = input >= 4096 /* compute 1's complement in case of */
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27 ? ((~input & 4095) << 1) + 33 /* negative samples */
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28 : (input << 1) + 33; /* NB: 33 is the difference value */
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29 /* between the thresholds for */
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30 /* A-law and u-law. */
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31 if (absno > (0x1FFF)) /* limitation to "absno" < 8192 */
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32 absno = (0x1FFF);
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33
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34 /* Determination of sample's segment */
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35 i = absno >> 6;
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36 segno = 1;
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37 while (i != 0) {
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38 segno++;
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39 i >>= 1;
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40 }
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41
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42 /* Mounting the high-nibble of the log-PCM sample */
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43 high_nibble = (0x0008) - segno;
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44
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45 /* Mounting the low-nibble of the log PCM sample */
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46 low_nibble = (absno >> segno) /* right shift of mantissa and */
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47 &(0x000F); /* masking away leading '1' */
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48 low_nibble = (0x000F) - low_nibble;
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50 /* Joining the high-nibble and the low-nibble of the log PCM sample */
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51 output = (high_nibble << 4) | low_nibble;
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52
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53 /* Add sign bit */
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54 if (input < 4096)
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55 output = output | (0x0080);
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56
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57 return output;
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58 }
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60 main(argc, argv)
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61 char **argv;
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62 {
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63 unsigned input, output;
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64
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65 for (input = 0; input < 8192; input++) {
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66 output = ulaw_compress(input);
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67 printf("%04o,", output);
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68 if ((input % 15) == 14 || input == 8191)
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69 putchar('\n');
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70 }
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71 exit(0);
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72 }