Asterisk - The Open Source Telephony Project GIT-master-2de1a68
alaw.h
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1/*
2 * Asterisk -- An open source telephony toolkit.
3 *
4 * Copyright (C) 1999 - 2005, Digium, Inc.
5 *
6 * Mark Spencer <markster@digium.com>
7 *
8 * See http://www.asterisk.org for more information about
9 * the Asterisk project. Please do not directly contact
10 * any of the maintainers of this project for assistance;
11 * the project provides a web site, mailing lists and IRC
12 * channels for your use.
13 *
14 * This program is free software, distributed under the terms of
15 * the GNU General Public License Version 2. See the LICENSE file
16 * at the top of the source tree.
17 */
18
19/*! \file
20 * \brief A-Law to Signed linear conversion
21 */
22
23#ifndef _ASTERISK_ALAW_H
24#define _ASTERISK_ALAW_H
25
26
27/*! \brief
28 * To init the alaw to slinear conversion stuff, this needs to be run.
29 */
30void ast_alaw_init(void);
31
32#define AST_ALAW_BIT_LOSS 4
33#define AST_ALAW_STEP (1 << AST_ALAW_BIT_LOSS)
34#define AST_ALAW_TAB_SIZE (32768 / AST_ALAW_STEP + 1)
35#define AST_ALAW_SIGN_BIT 0x80
36#define AST_ALAW_AMI_MASK 0x55
37
38
39/*! \brief converts signed linear to alaw */
40#ifndef G711_NEW_ALGORITHM
41extern unsigned char __ast_lin2a[8192];
42#else
43extern unsigned char __ast_lin2a[AST_ALAW_TAB_SIZE];
44#endif
45
46/*! help */
47extern short __ast_alaw[256];
48
49#ifndef G711_NEW_ALGORITHM
50#define AST_LIN2A(a) (__ast_lin2a[((unsigned short)(a)) >> 3])
51#else
52#define AST_LIN2A_LOOKUP(mag) \
53 __ast_lin2a[(mag) >> AST_ALAW_BIT_LOSS]
54
55/*! \brief Convert signed linear sample to sign-magnitude pair for a-Law */
56static inline void ast_alaw_get_sign_mag(short sample, unsigned *sign, unsigned *mag)
57{
58 /* It may look illogical to retrive the sign this way in both cases,
59 * but this helps gcc eliminate the branch below and produces
60 * faster code */
61 *sign = ((unsigned short)sample >> 8) & AST_ALAW_SIGN_BIT;
62#if defined(G711_REDUCED_BRANCHING)
63 {
64 unsigned dual_mag = (-sample << 16) | (unsigned short)sample;
65 *mag = (dual_mag >> (*sign >> 3)) & 0xffffU;
66 }
67#else
68 if (sample < 0)
69 *mag = -sample;
70 else
71 *mag = sample;
72#endif /* G711_REDUCED_BRANCHING */
73 *sign ^= AST_ALAW_SIGN_BIT;
74}
75
76static inline unsigned char AST_LIN2A(short sample)
77{
78 unsigned mag, sign;
79 ast_alaw_get_sign_mag(sample, &sign, &mag);
80 return (sign | AST_LIN2A_LOOKUP(mag)) ^ AST_ALAW_AMI_MASK;
81}
82#endif
83
84#define AST_ALAW(a) (__ast_alaw[(int)(a)])
85
86#endif /* _ASTERISK_ALAW_H */
#define AST_LIN2A(a)
Definition: alaw.h:50
#define AST_ALAW_AMI_MASK
Definition: alaw.h:36
unsigned char __ast_lin2a[8192]
converts signed linear to alaw
Definition: alaw.c:146
#define AST_ALAW_SIGN_BIT
Definition: alaw.h:35
short __ast_alaw[256]
Definition: alaw.c:150
void ast_alaw_init(void)
To init the alaw to slinear conversion stuff, this needs to be run.
Definition: alaw.c:152
#define AST_ALAW_TAB_SIZE
Definition: alaw.h:34