• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
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 
34 void 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