ref: 6e0fe794da9a0fbec8b55cd0700f599cf54f7d3a
dir: /src/libgsm/preprocess.c/
/*
* 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.
*/
#include <stdio.h>
#include <assert.h>
#include "private.h"
#include "gsm.h"
/* 4.2.0 .. 4.2.3 PREPROCESSING SECTION
*
* After A-law to linear conversion (or directly from the
* Ato D converter) the following scaling is assumed for
* input to the RPE-LTP algorithm:
*
* in: 0.1.....................12
* S.v.v.v.v.v.v.v.v.v.v.v.v.*.*.*
*
* Where S is the sign bit, v a valid bit, and * a "don't care" bit.
* The original signal is called sop[..]
*
* out: 0.1................... 12
* S.S.v.v.v.v.v.v.v.v.v.v.v.v.0.0
*/
void Gsm_Preprocess (
struct gsm_state * S,
word * s,
word * so ) /* [0..159] IN/OUT */
{
word z1 = S->z1;
longword L_z2 = S->L_z2;
word mp = S->mp;
word s1;
longword L_s2;
longword L_temp;
word msp, lsp;
word SO;
longword ltmp; /* for ADD */
ulongword utmp; /* for L_ADD */
register int k = 160;
while (k--) {
/* 4.2.1 Downscaling of the input signal
*/
SO = SASR( *s, 3 ) << 2;
s++;
assert (SO >= -0x4000); /* downscaled by */
assert (SO <= 0x3FFC); /* previous routine. */
/* 4.2.2 Offset compensation
*
* This part implements a high-pass filter and requires extended
* arithmetic precision for the recursive part of this filter.
* The input of this procedure is the array so[0...159] and the
* output the array sof[ 0...159 ].
*/
/* Compute the non-recursive part
*/
s1 = SO - z1; /* s1 = gsm_sub( *so, z1 ); */
z1 = SO;
assert(s1 != MIN_WORD);
/* Compute the recursive part
*/
L_s2 = s1;
L_s2 <<= 15;
/* Execution of a 31 bv 16 bits multiplication
*/
msp = SASR( L_z2, 15 );
lsp = L_z2-((longword)msp<<15); /* gsm_L_sub(L_z2,(msp<<15)); */
L_s2 += GSM_MULT_R( lsp, 32735 );
L_temp = (longword)msp * 32735; /* GSM_L_MULT(msp,32735) >> 1;*/
L_z2 = GSM_L_ADD( L_temp, L_s2 );
/* Compute sof[k] with rounding
*/
L_temp = GSM_L_ADD( L_z2, 16384 );
/* 4.2.3 Preemphasis
*/
msp = GSM_MULT_R( mp, -28180 );
mp = SASR( L_temp, 15 );
*so++ = GSM_ADD( mp, msp );
}
S->z1 = z1;
S->L_z2 = L_z2;
S->mp = mp;
}