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annotate libgsmfr2/tfo_dtxd.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 5a3535470c95
children
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5a3535470c95 libgsmfr2 TFO: implement DTXd function
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1 /*
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2 * The function implemented in this module is a post-processor to be invoked
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3 * after Rx DTX preproc functions if the Rx DTX handler block is used as a
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4 * TFO transform with DTXd enabled. It selectively transforms certain
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5 * preproc output frames (CN and silence frames specifically) into SID,
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6 * thereby allowing the network operator to reap the benefits of DTX on
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7 * the radio downlink leg.
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8 */
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9
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10 #include <stdint.h>
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11 #include "tw_gsmfr.h"
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12 #include "pp_state.h"
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13
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14 int gsmfr_tfo_xfrm_dtxd(struct gsmfr_preproc_state *st, uint8_t *frame)
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15 {
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16 uint8_t *p, sub;
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17
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18 if (!st->dtxd_sid_flag)
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19 return 1; /* SP=1: output is a speech frame */
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20 /* turn the output frame into SID */
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21 p = frame + 5; /* skip magic+LARc */
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22 for (sub = 0; sub < 4; sub++) {
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23 *p++ = 0;
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24 *p++ &= 0x1F; /* upper 5 bits of Xmaxc field */
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25 *p++ &= 0x80; /* and the lsb spilling into the next byte */
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26 *p++ = 0;
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27 *p++ = 0;
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28 *p++ = 0;
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29 *p++ = 0;
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30 }
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31 return 0; /* SP=0: output is SID */
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32 }