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annotate libgsmefr/lsp_lsf.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 bcd337afa0f1
children
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1 /*************************************************************************
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2 *
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3 * FUNCTIONS: Lsp_lsf and Lsf_lsp
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4 *
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5 * PURPOSE:
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6 * Lsp_lsf: Transformation lsp to lsf
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7 * Lsf_lsp: Transformation lsf to lsp
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8 *
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9 * DESCRIPTION:
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10 * lsp[i] = cos(2*pi*lsf[i]) and lsf[i] = arccos(lsp[i])/(2*pi)
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11 *
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12 * The transformation from lsp[i] to lsf[i] and lsf[i] to lsp[i] are
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13 * approximated by a look-up table and interpolation.
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14 *
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15 *************************************************************************/
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16
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17 #include "gsm_efr.h"
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18 #include "typedef.h"
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19 #include "namespace.h"
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20 #include "basic_op.h"
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21 #include "no_count.h"
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22 #include "sig_proc.h"
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24 #include "lsp_lsf.tab" /* Look-up table for transformations */
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25
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26 void Lsf_lsp (
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27 Word16 lsf[], /* (i) : lsf[m] normalized (range: 0.0<=val<=0.5) */
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28 Word16 lsp[], /* (o) : lsp[m] (range: -1<=val<1) */
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29 Word16 m /* (i) : LPC order */
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30 )
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31 {
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32 Word16 i, ind, offset;
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33 Word32 L_tmp;
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34
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35 for (i = 0; i < m; i++)
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36 {
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37 ind = shr (lsf[i], 8); /* ind = b8-b15 of lsf[i] */
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38 offset = lsf[i] & 0x00ff; logic16 (); /* offset = b0-b7 of lsf[i] */
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40 /* lsp[i] = table[ind]+ ((table[ind+1]-table[ind])*offset) / 256 */
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42 L_tmp = L_mult (sub (table[ind + 1], table[ind]), offset);
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43 lsp[i] = add (table[ind], extract_l (L_shr (L_tmp, 9)));
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44 move16 ();
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45 }
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46 return;
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47 }
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49 void Lsp_lsf (
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50 Word16 lsp[], /* (i) : lsp[m] (range: -1<=val<1) */
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51 Word16 lsf[], /* (o) : lsf[m] normalized (range: 0.0<=val<=0.5) */
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52 Word16 m /* (i) : LPC order */
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53 )
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54 {
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55 Word16 i, ind;
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56 Word32 L_tmp;
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58 ind = 63; /* begin at end of table -1 */
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60 for (i = m - 1; i >= 0; i--)
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61 {
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62 /* find value in table that is just greater than lsp[i] */
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63 test ();
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64 while (table[ind] < lsp[i])
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65 {
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66 ind--;
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67 test ();
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68 }
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70 /* acos(lsp[i])= ind*256 + ( ( lsp[i]-table[ind] ) *
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71 slope[ind] )/4096 */
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73 L_tmp = L_mult (sub (lsp[i], table[ind]), slope[ind]);
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74 /*(lsp[i]-table[ind])*slope[ind])>>12*/
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75 lsf[i] = round (L_shl (L_tmp, 3)); move16 ();
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76 lsf[i] = add (lsf[i], shl (ind, 8)); move16 ();
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77 }
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78 return;
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79 }