aboutsummaryrefslogtreecommitdiffstats
path: root/main/alaw.c
blob: 8d35952068e7bee671f304e1d6ff269b5cb54047 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 1999 - 2005, Digium, Inc.
 *
 * Mark Spencer <markster@digium.com>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*! \file
 *
 * \brief a-Law to Signed linear conversion
 *
 * \author Mark Spencer <markster@digium.com> 
 */

#include "asterisk.h"

ASTERISK_FILE_VERSION(__FILE__, "$Revision$")

#include "asterisk/alaw.h"

#ifndef G711_NEW_ALGORITHM
#define AMI_MASK 0x55

static inline unsigned char linear2alaw(short int linear)
{
    int mask;
    int seg;
    int pcm_val;
    static int seg_end[8] =
		{
			0xFF, 0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF
		};
    
    pcm_val = linear;
    if (pcm_val >= 0) {
	    /* Sign (7th) bit = 1 */
	    mask = AMI_MASK | 0x80;
    } else {
	    /* Sign bit = 0 */
	    mask = AMI_MASK;
	    pcm_val = -pcm_val;
    }
	
    /* Convert the scaled magnitude to segment number. */
    for (seg = 0;  seg < 8;  seg++) {
	    if (pcm_val <= seg_end[seg])
		    break;
    }
    /* Combine the sign, segment, and quantization bits. */
    return  ((seg << 4) | ((pcm_val >> ((seg)  ?  (seg + 3)  :  4)) & 0x0F)) ^ mask;
}
#else
static unsigned char linear2alaw(short sample, int full_coding)
{
	static const unsigned exp_lut[128] = {
		1,1,2,2,3,3,3,3,
		4,4,4,4,4,4,4,4,
		5,5,5,5,5,5,5,5,
		5,5,5,5,5,5,5,5,
		6,6,6,6,6,6,6,6,
		6,6,6,6,6,6,6,6,
		6,6,6,6,6,6,6,6,
		6,6,6,6,6,6,6,6,
		7,7,7,7,7,7,7,7,
		7,7,7,7,7,7,7,7,
		7,7,7,7,7,7,7,7,
		7,7,7,7,7,7,7,7,
		7,7,7,7,7,7,7,7,
		7,7,7,7,7,7,7,7,
		7,7,7,7,7,7,7,7,
		7,7,7,7,7,7,7,7 };
	unsigned sign, exponent, mantissa, mag;
	unsigned char alawbyte;
	
	ast_alaw_get_sign_mag(sample, &sign, &mag);
	if (mag > 32767)
		mag = 32767;        /* clip the magnitude for -32768 */
	
	exponent = exp_lut[(mag >> 8) & 0x7f];
	mantissa = (mag >> (exponent + 3)) & 0x0f;
	if (mag < 0x100)
		exponent = 0;
	
	if (full_coding) {
		/* full encoding, with sign and xform */
		alawbyte = (unsigned char)(sign | (exponent << 4) | mantissa);
		alawbyte ^= AST_ALAW_AMI_MASK;
	} else {
		/* half-cooked coding -- mantissa+exponent only (for lookup tab) */
		alawbyte = (exponent << 4) | mantissa;
	}
	return alawbyte;
}
#endif

#ifndef G711_NEW_ALGORITHM
static inline short int alaw2linear (unsigned char alaw)
{
    int i;
    int seg;
	
    alaw ^= AMI_MASK;
    i = ((alaw & 0x0F) << 4) + 8 /* rounding error */;
    seg = (((int) alaw & 0x70) >> 4);
    if (seg)
	    i = (i + 0x100) << (seg - 1);
    return (short int) ((alaw & 0x80)  ?  i  :  -i);
}
#else
static inline short alaw2linear(unsigned char alawbyte)
{
	unsigned exponent, mantissa;
	short sample;
	
	alawbyte ^= AST_ALAW_AMI_MASK;
	exponent = (alawbyte & 0x70) >> 4;
	mantissa = alawbyte & 0x0f;
	sample = (mantissa << 4) + 8 /* rounding error */;
	if (exponent)
		sample = (sample + 0x100) << (exponent - 1);
	if (!(alawbyte & 0x80))
		sample = -sample;
	return sample;
}
#endif



#ifndef G711_NEW_ALGORITHM
unsigned char __ast_lin2a[8192];
#else
unsigned char __ast_lin2a[AST_ALAW_TAB_SIZE];
#endif
short __ast_alaw[256];

void ast_alaw_init(void)
{
	int i;
	/* 
	 *  Set up mu-law conversion table
	 */ 
#ifndef G711_NEW_ALGORITHM
	for (i = 0; i < 256; i++) {
		__ast_alaw[i] = alaw2linear(i);
	}
	/* set up the reverse (mu-law) conversion table */
	for (i = -32768; i < 32768; i++) {
		__ast_lin2a[((unsigned short)i) >> 3] = linear2alaw(i);
	}
#else
	for (i = 0; i < 256; i++) {
		__ast_alaw[i] = alaw2linear(i);
	}
	/* set up the reverse (a-law) conversion table */
	for (i = 0; i <= 32768; i += AST_ALAW_STEP) {
		AST_LIN2A_LOOKUP(i) = linear2alaw(i, 0 /* half-cooked */);
	}
#endif
	
#ifdef TEST_CODING_TABLES
	for (i = -32768; i < 32768; ++i) {
#ifndef G711_NEW_ALGORITHM
		unsigned char e1 = linear2alaw(i);
#else
		unsigned char e1 = linear2alaw(i, 1);
#endif
		short d1 = alaw2linear(e1);
		unsigned char e2 = AST_LIN2A(i);
		short d2 = alaw2linear(e2);
		short d3 = AST_ALAW(e1);
		
		if (e1 != e2 || d1 != d3 || d2 != d3) {
			ast_log(LOG_WARNING, "a-Law coding tables test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d\n",
					i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2);
		}
	}
	ast_log(LOG_NOTICE, "a-Law coding tables test complete.\n");
#endif /* TEST_CODING_TABLES */
	
#ifdef TEST_TANDEM_TRANSCODING
	/* tandem transcoding test */
	for (i = -32768; i < 32768; ++i) {
		unsigned char e1 = AST_LIN2A(i);
		short d1 = AST_ALAW(e1);
		unsigned char e2 = AST_LIN2A(d1);
		short d2 = AST_ALAW(e2);
		unsigned char e3 = AST_LIN2A(d2);
		short d3 = AST_ALAW(e3);
		
		if (e1 != e2 || e2 != e3 || d1 != d2 || d2 != d3) {
			ast_log(LOG_WARNING, "a-Law tandem transcoding test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d, d3=%d\n",
					i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2, (int)d3);
		}
	}
	ast_log(LOG_NOTICE, "a-Law tandem transcoding test complete.\n");
#endif /* TEST_TANDEM_TRANSCODING */
	
}