FreeCalypso > hg > efr-experiments
comparison src/lsp_lsf.c @ 0:56410792419a
src: original EFR source from ETSI
| author | Mychaela Falconia <falcon@freecalypso.org> |
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| date | Wed, 03 Apr 2024 05:31:37 +0000 |
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| -1:000000000000 | 0:56410792419a |
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| 1 /************************************************************************* | |
| 2 * | |
| 3 * FUNCTIONS: Lsp_lsf and Lsf_lsp | |
| 4 * | |
| 5 * PURPOSE: | |
| 6 * Lsp_lsf: Transformation lsp to lsf | |
| 7 * Lsf_lsp: Transformation lsf to lsp | |
| 8 * | |
| 9 * DESCRIPTION: | |
| 10 * lsp[i] = cos(2*pi*lsf[i]) and lsf[i] = arccos(lsp[i])/(2*pi) | |
| 11 * | |
| 12 * The transformation from lsp[i] to lsf[i] and lsf[i] to lsp[i] are | |
| 13 * approximated by a look-up table and interpolation. | |
| 14 * | |
| 15 *************************************************************************/ | |
| 16 | |
| 17 #include "typedef.h" | |
| 18 #include "basic_op.h" | |
| 19 #include "count.h" | |
| 20 | |
| 21 #include "lsp_lsf.tab" /* Look-up table for transformations */ | |
| 22 | |
| 23 void Lsf_lsp ( | |
| 24 Word16 lsf[], /* (i) : lsf[m] normalized (range: 0.0<=val<=0.5) */ | |
| 25 Word16 lsp[], /* (o) : lsp[m] (range: -1<=val<1) */ | |
| 26 Word16 m /* (i) : LPC order */ | |
| 27 ) | |
| 28 { | |
| 29 Word16 i, ind, offset; | |
| 30 Word32 L_tmp; | |
| 31 | |
| 32 for (i = 0; i < m; i++) | |
| 33 { | |
| 34 ind = shr (lsf[i], 8); /* ind = b8-b15 of lsf[i] */ | |
| 35 offset = lsf[i] & 0x00ff; logic16 (); /* offset = b0-b7 of lsf[i] */ | |
| 36 | |
| 37 /* lsp[i] = table[ind]+ ((table[ind+1]-table[ind])*offset) / 256 */ | |
| 38 | |
| 39 L_tmp = L_mult (sub (table[ind + 1], table[ind]), offset); | |
| 40 lsp[i] = add (table[ind], extract_l (L_shr (L_tmp, 9))); | |
| 41 move16 (); | |
| 42 } | |
| 43 return; | |
| 44 } | |
| 45 | |
| 46 void Lsp_lsf ( | |
| 47 Word16 lsp[], /* (i) : lsp[m] (range: -1<=val<1) */ | |
| 48 Word16 lsf[], /* (o) : lsf[m] normalized (range: 0.0<=val<=0.5) */ | |
| 49 Word16 m /* (i) : LPC order */ | |
| 50 ) | |
| 51 { | |
| 52 Word16 i, ind; | |
| 53 Word32 L_tmp; | |
| 54 | |
| 55 ind = 63; /* begin at end of table -1 */ | |
| 56 | |
| 57 for (i = m - 1; i >= 0; i--) | |
| 58 { | |
| 59 /* find value in table that is just greater than lsp[i] */ | |
| 60 test (); | |
| 61 while (sub (table[ind], lsp[i]) < 0) | |
| 62 { | |
| 63 ind--; | |
| 64 test (); | |
| 65 } | |
| 66 | |
| 67 /* acos(lsp[i])= ind*256 + ( ( lsp[i]-table[ind] ) * | |
| 68 slope[ind] )/4096 */ | |
| 69 | |
| 70 L_tmp = L_mult (sub (lsp[i], table[ind]), slope[ind]); | |
| 71 /*(lsp[i]-table[ind])*slope[ind])>>12*/ | |
| 72 lsf[i] = round (L_shl (L_tmp, 3)); move16 (); | |
| 73 lsf[i] = add (lsf[i], shl (ind, 8)); move16 (); | |
| 74 } | |
| 75 return; | |
| 76 } |