FreeCalypso > hg > gsm-codec-lib

annotate libgsmefr/preemph.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
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children
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1 /*---------------------------------------------------------------------*
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2 * routine preemphasis() *
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3 * ~~~~~~~~~~~~~~~~~~~~~ *
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4 * Preemphasis: filtering through 1 - g z^-1 *
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5 *---------------------------------------------------------------------*/
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7 #include "gsm_efr.h"
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8 #include "typedef.h"
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9 #include "namespace.h"
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10 #include "basic_op.h"
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11 #include "no_count.h"
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12 #include "sig_proc.h"
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13 #include "cnst.h"
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14 #include "dec_state.h"
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16 void preemphasis (
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17 struct EFR_decoder_state *st,
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18 Word16 *signal, /* (i/o) : input signal overwritten by the output */
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19 Word16 g, /* (i) : preemphasis coefficient */
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20 Word16 L /* (i) : size of filtering */
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21 )
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22 {
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23 Word16 *p1, *p2, temp, i;
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25 p1 = signal + L - 1;
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26 p2 = p1 - 1;
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27 temp = *p1;
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29 for (i = 0; i <= L - 2; i++)
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30 {
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31 *p1 = sub (*p1, mult (g, *p2--));
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32 p1--;
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33 }
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35 *p1 = sub (*p1, mult (g, st->mem_pre));
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37 st->mem_pre = temp;
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39 return;
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40 }