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annotate libgsmfr2/prng.c @ 585:3c6bf0d26ee7 default tip

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TW-TS-005 reader: fix maximum line length bug TW-TS-005 section 4.1 states: The maximum allowed length of each line is 80 characters, not including the OS-specific newline encoding. The implementation of this line length limit in the TW-TS-005 hex file reader function in the present suite was wrong, such that lines of the full maximum length could not be read. Fix it. Note that this bug affects comment lines too, not just actual RTP payloads. Neither Annex A nor Annex B features an RTP payload format that goes to the maximum of 40 bytes, but if a comment line goes to the maximum allowed length of 80 characters not including the terminating newline, the bug will be triggered, necessitating the present fix.
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 25 Feb 2025 07:49:28 +0000
parents 573afa985df6
children
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1 /*
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2 * We use a pseudorandom sequence generator function in two places:
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3 * when generating comfort noise (GSM 06.12 section 6.1), and when
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4 * randomizing grid position parameters as part of speech muting
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5 * during error handling (GSM 06.11 section 6).
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6 *
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7 * Our PRNG is a copy of the pseudonoise() function from ETSI EFR code,
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8 * where it is used for similar purposes.
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9 */
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11 #include <stdint.h>
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12 #include "tw_gsmfr.h"
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13 #include "pp_state.h"
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14 #include "pp_internal.h"
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16 uint16_t gsmfr_preproc_prng(struct gsmfr_preproc_state *st, uint16_t no_bits)
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17 {
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18 uint16_t noise_bits, Sn, i;
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20 noise_bits = 0;
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21 for (i = 0; i < no_bits; i++)
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22 {
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23 /* State n == 31 */
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24 if ((st->cn_random_lfsr & 0x00000001L) != 0)
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25 {
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26 Sn = 1;
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27 }
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28 else
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29 {
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30 Sn = 0;
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31 }
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32
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33 /* State n == 3 */
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34 if ((st->cn_random_lfsr & 0x10000000L) != 0)
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35 {
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36 Sn = Sn ^ 1;
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37 }
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38 else
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39 {
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40 Sn = Sn ^ 0;
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41 }
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43 noise_bits = noise_bits << 1;
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44 noise_bits = noise_bits | st->cn_random_lfsr & 1;
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45
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46 st->cn_random_lfsr >>= 1;
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47 if (Sn & 1)
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48 {
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49 st->cn_random_lfsr |= 0x40000000L;
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50 }
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51 }
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53 return noise_bits;
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54 }