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annotate libgsmefr/lsp_lsf.c @ 485:751f06541fbb

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doc/Codec-utils: clarify lack of DHF in gsmfr-decode-rb
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 20 May 2024 01:47:22 +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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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 }