1/*
2 * Copyright 1992 by Jutta Degener and Carsten Bormann, Technische
3 * Universitaet Berlin.  See the accompanying file "COPYRIGHT" for
4 * details.  THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
5 */
6
7/* $Header: /tmp_amd/presto/export/kbs/jutta/src/gsm/RCS/preprocess.c,v 1.2 1994/05/10 20:18:45 jutta Exp $ */
8
9#include	<stdio.h>
10#include	<assert.h>
11
12#include "private.h"
13
14#include	"gsm.h"
15#include 	"proto.h"
16
17/*	4.2.0 .. 4.2.3	PREPROCESSING SECTION
18 *
19 *  	After A-law to linear conversion (or directly from the
20 *   	Ato D converter) the following scaling is assumed for
21 * 	input to the RPE-LTP algorithm:
22 *
23 *      in:  0.1.....................12
24 *	     S.v.v.v.v.v.v.v.v.v.v.v.v.*.*.*
25 *
26 *	Where S is the sign bit, v a valid bit, and * a "don't care" bit.
27 * 	The original signal is called sop[..]
28 *
29 *      out:   0.1................... 12
30 *	     S.S.v.v.v.v.v.v.v.v.v.v.v.v.0.0
31 */
32
33
34void Gsm_Preprocess P3((S, s, so),
35	struct gsm_state * S,
36	word		 * s,
37	word 		 * so )		/* [0..159] 	IN/OUT	*/
38{
39
40	word       z1 = S->z1;
41	longword L_z2 = S->L_z2;
42	word 	   mp = S->mp;
43
44	word 	   	s1;
45	longword      L_s2;
46
47	longword      L_temp;
48
49	word		msp, lsp;
50	word		SO;
51
52	longword	ltmp;		/* for   ADD */
53	ulongword	utmp;		/* for L_ADD */
54
55	register int		k = 160;
56
57	while (k--) {
58
59	/*  4.2.1   Downscaling of the input signal
60	 */
61		SO = SASR( *s, 3 ) << 2;
62		s++;
63
64		assert (SO >= -0x4000);	/* downscaled by     */
65		assert (SO <=  0x3FFC);	/* previous routine. */
66
67
68	/*  4.2.2   Offset compensation
69	 *
70	 *  This part implements a high-pass filter and requires extended
71	 *  arithmetic precision for the recursive part of this filter.
72	 *  The input of this procedure is the array so[0...159] and the
73	 *  output the array sof[ 0...159 ].
74	 */
75		/*   Compute the non-recursive part
76		 */
77
78		s1 = SO - z1;			/* s1 = gsm_sub( *so, z1 ); */
79		z1 = SO;
80
81		assert(s1 != MIN_WORD);
82
83		/*   Compute the recursive part
84		 */
85		L_s2 = s1;
86		L_s2 <<= 15;
87
88		/*   Execution of a 31 bv 16 bits multiplication
89		 */
90
91		msp = SASR( L_z2, 15 );
92		lsp = L_z2-((longword)msp<<15); /* gsm_L_sub(L_z2,(msp<<15)); */
93
94		L_s2  += GSM_MULT_R( lsp, 32735 );
95		L_temp = (longword)msp * 32735; /* GSM_L_MULT(msp,32735) >> 1;*/
96		L_z2   = GSM_L_ADD( L_temp, L_s2 );
97
98		/*    Compute sof[k] with rounding
99		 */
100		L_temp = GSM_L_ADD( L_z2, 16384 );
101
102	/*   4.2.3  Preemphasis
103	 */
104
105		msp   = GSM_MULT_R( mp, -28180 );
106		mp    = SASR( L_temp, 15 );
107		*so++ = GSM_ADD( mp, msp );
108	}
109
110	S->z1   = z1;
111	S->L_z2 = L_z2;
112	S->mp   = mp;
113}
114