Asterisk - The Open Source Telephony Project  18.5.0
Macros | Functions | Variables
alaw.c File Reference

a-Law to Signed linear conversion More...

#include "asterisk.h"
#include "asterisk/alaw.h"
#include "asterisk/logger.h"
Include dependency graph for alaw.c:

Go to the source code of this file.

Macros

#define AMI_MASK   0x55
 

Functions

static short int alaw2linear (unsigned char alaw)
 
void ast_alaw_init (void)
 To init the alaw to slinear conversion stuff, this needs to be run. More...
 
static unsigned char linear2alaw (short int linear)
 

Variables

short __ast_alaw [256]
 
unsigned char __ast_lin2a [8192]
 converts signed linear to alaw More...
 

Detailed Description

a-Law to Signed linear conversion

Author
Mark Spencer marks.nosp@m.ter@.nosp@m.digiu.nosp@m.m.co.nosp@m.m

Definition in file alaw.c.

Macro Definition Documentation

◆ AMI_MASK

#define AMI_MASK   0x55

Definition at line 36 of file alaw.c.

Referenced by alaw2linear(), and linear2alaw().

Function Documentation

◆ alaw2linear()

static short int alaw2linear ( unsigned char  alaw)
inlinestatic

Definition at line 112 of file alaw.c.

References AMI_MASK, and AST_ALAW_AMI_MASK.

Referenced by ast_alaw_init().

113 {
114  int i;
115  int seg;
116 
117  alaw ^= AMI_MASK;
118  i = ((alaw & 0x0F) << 4) + 8 /* rounding error */;
119  seg = (((int) alaw & 0x70) >> 4);
120  if (seg) {
121  i = (i + 0x100) << (seg - 1);
122  }
123  return (short int) ((alaw & 0x80) ? i : -i);
124 }
static struct ast_codec alaw
#define AMI_MASK
Definition: alaw.c:36

◆ ast_alaw_init()

void ast_alaw_init ( void  )

To init the alaw to slinear conversion stuff, this needs to be run.

Definition at line 152 of file alaw.c.

References __ast_alaw, __ast_lin2a, alaw2linear(), AST_ALAW, AST_ALAW_STEP, AST_LIN2A, ast_log, linear2alaw(), LOG_NOTICE, and LOG_WARNING.

Referenced by asterisk_daemon().

153 {
154  int i;
155  /*
156  * Set up mu-law conversion table
157  */
158 #ifndef G711_NEW_ALGORITHM
159  for (i = 0; i < 256; i++) {
160  __ast_alaw[i] = alaw2linear(i);
161  }
162  /* set up the reverse (mu-law) conversion table */
163  for (i = -32768; i < 32768; i++) {
164  __ast_lin2a[((unsigned short)i) >> 3] = linear2alaw(i);
165  }
166 #else
167  for (i = 0; i < 256; i++) {
168  __ast_alaw[i] = alaw2linear(i);
169  }
170  /* set up the reverse (a-law) conversion table */
171  for (i = 0; i <= 32768; i += AST_ALAW_STEP) {
172  AST_LIN2A_LOOKUP(i) = linear2alaw(i, 0 /* half-cooked */);
173  }
174 #endif
175 
176 #ifdef TEST_CODING_TABLES
177  for (i = -32768; i < 32768; ++i) {
178 #ifndef G711_NEW_ALGORITHM
179  unsigned char e1 = linear2alaw(i);
180 #else
181  unsigned char e1 = linear2alaw(i, 1);
182 #endif
183  short d1 = alaw2linear(e1);
184  unsigned char e2 = AST_LIN2A(i);
185  short d2 = alaw2linear(e2);
186  short d3 = AST_ALAW(e1);
187 
188  if (e1 != e2 || d1 != d3 || d2 != d3) {
189  ast_log(LOG_WARNING, "a-Law coding tables test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d\n",
190  i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2);
191  }
192  }
193  ast_log(LOG_NOTICE, "a-Law coding tables test complete.\n");
194 #endif /* TEST_CODING_TABLES */
195 
196 #ifdef TEST_TANDEM_TRANSCODING
197  /* tandem transcoding test */
198  for (i = -32768; i < 32768; ++i) {
199  unsigned char e1 = AST_LIN2A(i);
200  short d1 = AST_ALAW(e1);
201  unsigned char e2 = AST_LIN2A(d1);
202  short d2 = AST_ALAW(e2);
203  unsigned char e3 = AST_LIN2A(d2);
204  short d3 = AST_ALAW(e3);
205 
206  if (e1 != e2 || e2 != e3 || d1 != d2 || d2 != d3) {
207  ast_log(LOG_WARNING, "a-Law tandem transcoding test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d, d3=%d\n",
208  i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2, (int)d3);
209  }
210  }
211  ast_log(LOG_NOTICE, "a-Law tandem transcoding test complete.\n");
212 #endif /* TEST_TANDEM_TRANSCODING */
213 
214 }
unsigned char __ast_lin2a[8192]
converts signed linear to alaw
Definition: alaw.c:146
short __ast_alaw[256]
Definition: alaw.c:150
#define LOG_WARNING
Definition: logger.h:274
#define AST_ALAW(a)
Definition: alaw.h:84
#define ast_log
Definition: astobj2.c:42
#define AST_ALAW_STEP
Definition: alaw.h:33
static short int alaw2linear(unsigned char alaw)
Definition: alaw.c:112
#define LOG_NOTICE
Definition: logger.h:263
static unsigned char linear2alaw(short int linear)
Definition: alaw.c:38
#define AST_LIN2A(a)
Definition: alaw.h:50

◆ linear2alaw()

static unsigned char linear2alaw ( short int  linear)
inlinestatic

Definition at line 38 of file alaw.c.

References AMI_MASK, and AST_ALAW_AMI_MASK.

Referenced by ast_alaw_init().

39 {
40  int mask;
41  int seg;
42  int pcm_val;
43  static int seg_end[8] =
44  {
45  0xFF, 0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF
46  };
47 
48  pcm_val = linear;
49  if (pcm_val >= 0) {
50  /* Sign (7th) bit = 1 */
51  mask = AMI_MASK | 0x80;
52  } else {
53  /* Sign bit = 0 */
54  mask = AMI_MASK;
55  pcm_val = -pcm_val;
56  }
57 
58  /* Convert the scaled magnitude to segment number. */
59  for (seg = 0; seg < 8; seg++) {
60  if (pcm_val <= seg_end[seg]) {
61  break;
62  }
63  }
64  /* Combine the sign, segment, and quantization bits. */
65  return ((seg << 4) | ((pcm_val >> ((seg) ? (seg + 3) : 4)) & 0x0F)) ^ mask;
66 }
#define AMI_MASK
Definition: alaw.c:36

Variable Documentation

◆ __ast_alaw

short __ast_alaw[256]

help

Definition at line 150 of file alaw.c.

Referenced by ast_alaw_init().

◆ __ast_lin2a

unsigned char __ast_lin2a[8192]

converts signed linear to alaw

Definition at line 146 of file alaw.c.

Referenced by ast_alaw_init().