74 lines
1.8 KiB
C
74 lines
1.8 KiB
C
/*
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ITU-T G.729A Speech Coder ANSI-C Source Code
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Version 1.1 Last modified: September 1996
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Copyright (c) 1996,
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AT&T, France Telecom, NTT, Universite de Sherbrooke
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All rights reserved.
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*/
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/*-----------------------------------------------------------*
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* Function Decod_ACELP() *
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* ~~~~~~~~~~~~~~~~~~~~~~~ *
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* Algebraic codebook decoder. *
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*----------------------------------------------------------*/
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#include "typedef.h"
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#include "basic_op.h"
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#include "ld8a.h"
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void
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Decod_ACELP (Word16 sign, /* (i) : signs of 4 pulses. */
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Word16 index, /* (i) : Positions of the 4 pulses. */
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Word16 cod[] /* (o) Q13 : algebraic (fixed) codebook excitation */
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)
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{
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Word16 i, j;
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Word16 pos[4];
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/* Decode the positions */
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i = index & (Word16) 7;
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pos[0] = add (i, shl (i, 2)); /* pos0 =i*5 */
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index = shr (index, 3);
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i = index & (Word16) 7;
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i = add (i, shl (i, 2)); /* pos1 =i*5+1 */
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pos[1] = add (i, 1);
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index = shr (index, 3);
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i = index & (Word16) 7;
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i = add (i, shl (i, 2)); /* pos2 =i*5+1 */
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pos[2] = add (i, 2);
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index = shr (index, 3);
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j = index & (Word16) 1;
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index = shr (index, 1);
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i = index & (Word16) 7;
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i = add (i, shl (i, 2)); /* pos3 =i*5+3+j */
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i = add (i, 3);
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pos[3] = add (i, j);
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/* decode the signs and build the codeword */
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for (i = 0; i < L_SUBFR; i++) {
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cod[i] = 0;
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}
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for (j = 0; j < 4; j++) {
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i = sign & (Word16) 1;
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sign = shr (sign, 1);
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if (i != 0) {
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cod[pos[j]] = 8191; /* Q13 +1.0 */
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}
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else {
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cod[pos[j]] = -8192; /* Q13 -1.0 */
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}
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}
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return;
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}
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