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annotate src/lsp_lsf.c @ 8:8b17df8f6340 default tip

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author Mychaela Falconia <falcon@freecalypso.org>
date Wed, 17 Apr 2024 17:30:25 +0000
parents 56410792419a
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 "typedef.h"
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18 #include "basic_op.h"
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19 #include "count.h"
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20
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21 #include "lsp_lsf.tab" /* Look-up table for transformations */
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22
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23 void Lsf_lsp (
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24 Word16 lsf[], /* (i) : lsf[m] normalized (range: 0.0<=val<=0.5) */
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25 Word16 lsp[], /* (o) : lsp[m] (range: -1<=val<1) */
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26 Word16 m /* (i) : LPC order */
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27 )
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28 {
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29 Word16 i, ind, offset;
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30 Word32 L_tmp;
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31
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32 for (i = 0; i < m; i++)
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33 {
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34 ind = shr (lsf[i], 8); /* ind = b8-b15 of lsf[i] */
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35 offset = lsf[i] & 0x00ff; logic16 (); /* offset = b0-b7 of lsf[i] */
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36
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37 /* lsp[i] = table[ind]+ ((table[ind+1]-table[ind])*offset) / 256 */
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38
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39 L_tmp = L_mult (sub (table[ind + 1], table[ind]), offset);
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40 lsp[i] = add (table[ind], extract_l (L_shr (L_tmp, 9)));
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41 move16 ();
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42 }
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43 return;
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44 }
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45
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46 void Lsp_lsf (
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47 Word16 lsp[], /* (i) : lsp[m] (range: -1<=val<1) */
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48 Word16 lsf[], /* (o) : lsf[m] normalized (range: 0.0<=val<=0.5) */
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49 Word16 m /* (i) : LPC order */
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50 )
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51 {
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52 Word16 i, ind;
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53 Word32 L_tmp;
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54
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55 ind = 63; /* begin at end of table -1 */
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56
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57 for (i = m - 1; i >= 0; i--)
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58 {
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59 /* find value in table that is just greater than lsp[i] */
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60 test ();
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61 while (sub (table[ind], lsp[i]) < 0)
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62 {
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63 ind--;
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64 test ();
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65 }
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66
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67 /* acos(lsp[i])= ind*256 + ( ( lsp[i]-table[ind] ) *
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68 slope[ind] )/4096 */
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69
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70 L_tmp = L_mult (sub (lsp[i], table[ind]), slope[ind]);
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71 /*(lsp[i]-table[ind])*slope[ind])>>12*/
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72 lsf[i] = round (L_shl (L_tmp, 3)); move16 ();
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73 lsf[i] = add (lsf[i], shl (ind, 8)); move16 ();
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74 }
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75 return;
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76 }