libsndfile source files.
[Faustine.git] / interpretor / libsndfile-1.0.25 / src / GSM610 / preprocess.c
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 #include <stdio.h>
8 #include <assert.h>
9
10 #include "gsm610_priv.h"
11
12 /* 4.2.0 .. 4.2.3 PREPROCESSING SECTION
13 *
14 * After A-law to linear conversion (or directly from the
15 * Ato D converter) the following scaling is assumed for
16 * input to the RPE-LTP algorithm:
17 *
18 * in: 0.1.....................12
19 * S.v.v.v.v.v.v.v.v.v.v.v.v.*.*.*
20 *
21 * Where S is the sign bit, v a valid bit, and * a "don't care" bit.
22 * The original signal is called sop[..]
23 *
24 * out: 0.1................... 12
25 * S.S.v.v.v.v.v.v.v.v.v.v.v.v.0.0
26 */
27
28
29 void Gsm_Preprocess (
30 struct gsm_state * S,
31 word * s,
32 word * so ) /* [0..159] IN/OUT */
33 {
34
35 word z1 = S->z1;
36 longword L_z2 = S->L_z2;
37 word mp = S->mp;
38
39 word s1;
40 longword L_s2;
41
42 longword L_temp;
43
44 word msp, lsp;
45 word SO;
46
47 register int k = 160;
48
49 while (k--) {
50
51 /* 4.2.1 Downscaling of the input signal
52 */
53 SO = SASR_W( *s, 3 ) << 2;
54 s++;
55
56 assert (SO >= -0x4000); /* downscaled by */
57 assert (SO <= 0x3FFC); /* previous routine. */
58
59
60 /* 4.2.2 Offset compensation
61 *
62 * This part implements a high-pass filter and requires extended
63 * arithmetic precision for the recursive part of this filter.
64 * The input of this procedure is the array so[0...159] and the
65 * output the array sof[ 0...159 ].
66 */
67 /* Compute the non-recursive part
68 */
69
70 s1 = SO - z1; /* s1 = gsm_sub( *so, z1 ); */
71 z1 = SO;
72
73 assert(s1 != MIN_WORD);
74
75 /* Compute the recursive part
76 */
77 L_s2 = s1;
78 L_s2 <<= 15;
79
80 /* Execution of a 31 bv 16 bits multiplication
81 */
82
83 msp = SASR_L( L_z2, 15 );
84 lsp = L_z2-((longword)msp<<15); /* gsm_L_sub(L_z2,(msp<<15)); */
85
86 L_s2 += GSM_MULT_R( lsp, 32735 );
87 L_temp = (longword)msp * 32735; /* GSM_L_MULT(msp,32735) >> 1;*/
88 L_z2 = GSM_L_ADD( L_temp, L_s2 );
89
90 /* Compute sof[k] with rounding
91 */
92 L_temp = GSM_L_ADD( L_z2, 16384 );
93
94 /* 4.2.3 Preemphasis
95 */
96
97 msp = GSM_MULT_R( mp, -28180 );
98 mp = SASR_L( L_temp, 15 );
99 *so++ = GSM_ADD( mp, msp );
100 }
101
102 S->z1 = z1;
103 S->L_z2 = L_z2;
104 S->mp = mp;
105 }