114 lines
2.5 KiB
C
114 lines
2.5 KiB
C
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/*
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* Copyright 1992 by Jutta Degener and Carsten Bormann, Technische
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* Universitaet Berlin. See the accompanying file "COPYRIGHT" for
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* details. THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
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*/
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/* $Header: /tmp_amd/presto/export/kbs/jutta/src/gsm/RCS/preprocess.c,v 1.2 1994/05/10 20:18:45 jutta Exp $ */
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#include <stdio.h>
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#include <assert.h>
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#include "private.h"
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#include "gsm.h"
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#include "proto.h"
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/* 4.2.0 .. 4.2.3 PREPROCESSING SECTION
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*
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* After A-law to linear conversion (or directly from the
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* Ato D converter) the following scaling is assumed for
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* input to the RPE-LTP algorithm:
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*
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* in: 0.1.....................12
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* S.v.v.v.v.v.v.v.v.v.v.v.v.*.*.*
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*
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* Where S is the sign bit, v a valid bit, and * a "don't care" bit.
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* The original signal is called sop[..]
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*
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* out: 0.1................... 12
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* S.S.v.v.v.v.v.v.v.v.v.v.v.v.0.0
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*/
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void Gsm_Preprocess P3((S, s, so),
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struct gsm_state * S,
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word * s,
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word * so ) /* [0..159] IN/OUT */
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{
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word z1 = S->z1;
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longword L_z2 = S->L_z2;
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word mp = S->mp;
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word s1;
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longword L_s2;
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longword L_temp;
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word msp, lsp;
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word SO;
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longword ltmp; /* for ADD */
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ulongword utmp; /* for L_ADD */
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register int k = 160;
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while (k--) {
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/* 4.2.1 Downscaling of the input signal
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*/
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SO = SASR( *s, 3 ) << 2;
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s++;
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assert (SO >= -0x4000); /* downscaled by */
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assert (SO <= 0x3FFC); /* previous routine. */
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/* 4.2.2 Offset compensation
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*
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* This part implements a high-pass filter and requires extended
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* arithmetic precision for the recursive part of this filter.
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* The input of this procedure is the array so[0...159] and the
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* output the array sof[ 0...159 ].
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*/
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/* Compute the non-recursive part
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*/
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s1 = SO - z1; /* s1 = gsm_sub( *so, z1 ); */
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z1 = SO;
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assert(s1 != MIN_WORD);
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/* Compute the recursive part
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*/
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L_s2 = s1;
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L_s2 <<= 15;
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/* Execution of a 31 bv 16 bits multiplication
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*/
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msp = SASR( L_z2, 15 );
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lsp = L_z2-((longword)msp<<15); /* gsm_L_sub(L_z2,(msp<<15)); */
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L_s2 += GSM_MULT_R( lsp, 32735 );
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L_temp = (longword)msp * 32735; /* GSM_L_MULT(msp,32735) >> 1;*/
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L_z2 = GSM_L_ADD( L_temp, L_s2 );
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/* Compute sof[k] with rounding
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*/
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L_temp = GSM_L_ADD( L_z2, 16384 );
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/* 4.2.3 Preemphasis
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*/
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msp = GSM_MULT_R( mp, -28180 );
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mp = SASR( L_temp, 15 );
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*so++ = GSM_ADD( mp, msp );
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}
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S->z1 = z1;
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S->L_z2 = L_z2;
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S->mp = mp;
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}
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