code.c

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/*
 * Copyright 1992 by Jutta Degener and Carsten Bormann, Technische
 * Universitaet Berlin. See the accompanying file "COPYRIGHT" for
 * details. THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
 */

/* $Header$ */

#include "config.h"

#ifdef HAS_STRING_H
#include <string.h>
#else
# include "proto.h"
 extern char * memcpy P((char *, char *, int));
#endif

#include "private.h"
#include "gsm.h"
#include "proto.h"

/*
 * 4.2 FIXED POINT IMPLEMENTATION OF THE RPE-LTP CODER
 */

void Gsm_Coder P8((S,s,LARc,Nc,bc,Mc,xmaxc,xMc),

 struct gsm_state * S,

 word * s, /* [0..159] samples IN */

/*
 * The RPE-LTD coder works on a frame by frame basis. The length of
 * the frame is equal to 160 samples. Some computations are done
 * once per frame to produce at the output of the coder the
 * LARc[1..8] parameters which are the coded LAR coefficients and
 * also to realize the inverse filtering operation for the entire
 * frame (160 samples of signal d[0..159]). These parts produce at
 * the output of the coder:
 */

 word * LARc, /* [0..7] LAR coefficients OUT */

/*
 * Procedure 4.2.11 to 4.2.18 are to be executed four times per
 * frame. That means once for each sub-segment RPE-LTP analysis of
 * 40 samples. These parts produce at the output of the coder:
 */

 word * Nc, /* [0..3] LTP lag OUT */
 word * bc, /* [0..3] coded LTP gain OUT */
 word * Mc, /* [0..3] RPE grid selection OUT */
 word * xmaxc,/* [0..3] Coded maximum amplitude OUT */
 word * xMc /* [13*4] normalized RPE samples OUT */
)
{
 int k;
 word * dp = S->dp0 + 120; /* [ -120...-1 ] */
 word * dpp = dp; /* [ 0...39 ] */

 word e[50];

 word so[160];

 memset(e,0,sizeof e);
 Gsm_Preprocess (S, s, so);
 Gsm_LPC_Analysis (S, so, LARc);
 Gsm_Short_Term_Analysis_Filter (S, LARc, so);

 for (k = 0; k <= 3; k++, xMc += 13) {

 Gsm_Long_Term_Predictor ( S,
 so+k*40, /* d [0..39] IN */
 dp, /* dp [-120..-1] IN */
 e + 5, /* e [0..39] OUT */
 dpp, /* dpp [0..39] OUT */
 Nc++,
 bc++);

 Gsm_RPE_Encoding ( S,
 e + 5, /* e ][0..39][ IN/OUT */
 xmaxc++, Mc++, xMc );
 /*
 * Gsm_Update_of_reconstructed_short_time_residual_signal
 * ( dpp, e + 5, dp );
 */

 { register int i;
 for (i = 0; i <= 39; i++)
 dp[ i ] = GSM_ADD( e[5 + i], dpp[i] );
 }
 dp += 40;
 dpp += 40;

 }
 (void)memcpy( (char *)S->dp0, (char *)(S->dp0 + 160),
 120 * sizeof(*S->dp0) );
}