Wed Jan 8 2020 09:49:52

Asterisk developer's documentation


alaw.c File Reference

a-Law to Signed linear conversion More...

#include "asterisk.h"
#include "asterisk/alaw.h"
#include "asterisk/logger.h"

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

#define AMI_MASK   0x55

Definition at line 38 of file alaw.c.

Referenced by alaw2linear(), and linear2alaw().

Function Documentation

static short int alaw2linear ( unsigned char  alaw)
inlinestatic

Definition at line 114 of file alaw.c.

References AMI_MASK.

Referenced by ast_alaw_init().

115 {
116  int i;
117  int seg;
118 
119  alaw ^= AMI_MASK;
120  i = ((alaw & 0x0F) << 4) + 8 /* rounding error */;
121  seg = (((int) alaw & 0x70) >> 4);
122  if (seg) {
123  i = (i + 0x100) << (seg - 1);
124  }
125  return (short int) ((alaw & 0x80) ? i : -i);
126 }
#define AMI_MASK
Definition: alaw.c:38
void ast_alaw_init ( void  )

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

Definition at line 154 of file alaw.c.

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

Referenced by main().

155 {
156  int i;
157  /*
158  * Set up mu-law conversion table
159  */
160 #ifndef G711_NEW_ALGORITHM
161  for (i = 0; i < 256; i++) {
162  __ast_alaw[i] = alaw2linear(i);
163  }
164  /* set up the reverse (mu-law) conversion table */
165  for (i = -32768; i < 32768; i++) {
166  __ast_lin2a[((unsigned short)i) >> 3] = linear2alaw(i);
167  }
168 #else
169  for (i = 0; i < 256; i++) {
170  __ast_alaw[i] = alaw2linear(i);
171  }
172  /* set up the reverse (a-law) conversion table */
173  for (i = 0; i <= 32768; i += AST_ALAW_STEP) {
174  AST_LIN2A_LOOKUP(i) = linear2alaw(i, 0 /* half-cooked */);
175  }
176 #endif
177 
178 #ifdef TEST_CODING_TABLES
179  for (i = -32768; i < 32768; ++i) {
180 #ifndef G711_NEW_ALGORITHM
181  unsigned char e1 = linear2alaw(i);
182 #else
183  unsigned char e1 = linear2alaw(i, 1);
184 #endif
185  short d1 = alaw2linear(e1);
186  unsigned char e2 = AST_LIN2A(i);
187  short d2 = alaw2linear(e2);
188  short d3 = AST_ALAW(e1);
189 
190  if (e1 != e2 || d1 != d3 || d2 != d3) {
191  ast_log(LOG_WARNING, "a-Law coding tables test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d\n",
192  i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2);
193  }
194  }
195  ast_log(LOG_NOTICE, "a-Law coding tables test complete.\n");
196 #endif /* TEST_CODING_TABLES */
197 
198 #ifdef TEST_TANDEM_TRANSCODING
199  /* tandem transcoding test */
200  for (i = -32768; i < 32768; ++i) {
201  unsigned char e1 = AST_LIN2A(i);
202  short d1 = AST_ALAW(e1);
203  unsigned char e2 = AST_LIN2A(d1);
204  short d2 = AST_ALAW(e2);
205  unsigned char e3 = AST_LIN2A(d2);
206  short d3 = AST_ALAW(e3);
207 
208  if (e1 != e2 || e2 != e3 || d1 != d2 || d2 != d3) {
209  ast_log(LOG_WARNING, "a-Law tandem transcoding test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d, d3=%d\n",
210  i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2, (int)d3);
211  }
212  }
213  ast_log(LOG_NOTICE, "a-Law tandem transcoding test complete.\n");
214 #endif /* TEST_TANDEM_TRANSCODING */
215 
216 }
#define LOG_WARNING
Definition: logger.h:144
#define AST_ALAW(a)
Definition: alaw.h:84
short __ast_alaw[256]
Definition: alaw.c:152
unsigned char __ast_lin2a[8192]
converts signed linear to alaw
Definition: alaw.c:148
#define AST_ALAW_STEP
Definition: alaw.h:33
static short int alaw2linear(unsigned char alaw)
Definition: alaw.c:114
void ast_log(int level, const char *file, int line, const char *function, const char *fmt,...)
Used for sending a log message This is the standard logger function. Probably the only way you will i...
Definition: logger.c:1207
#define LOG_NOTICE
Definition: logger.h:133
static unsigned char linear2alaw(short int linear)
Definition: alaw.c:40
#define AST_LIN2A(a)
Definition: alaw.h:50
static unsigned char linear2alaw ( short int  linear)
inlinestatic

Definition at line 40 of file alaw.c.

References AMI_MASK.

Referenced by ast_alaw_init().

41 {
42  int mask;
43  int seg;
44  int pcm_val;
45  static int seg_end[8] =
46  {
47  0xFF, 0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF
48  };
49 
50  pcm_val = linear;
51  if (pcm_val >= 0) {
52  /* Sign (7th) bit = 1 */
53  mask = AMI_MASK | 0x80;
54  } else {
55  /* Sign bit = 0 */
56  mask = AMI_MASK;
57  pcm_val = -pcm_val;
58  }
59 
60  /* Convert the scaled magnitude to segment number. */
61  for (seg = 0; seg < 8; seg++) {
62  if (pcm_val <= seg_end[seg]) {
63  break;
64  }
65  }
66  /* Combine the sign, segment, and quantization bits. */
67  return ((seg << 4) | ((pcm_val >> ((seg) ? (seg + 3) : 4)) & 0x0F)) ^ mask;
68 }
#define AMI_MASK
Definition: alaw.c:38

Variable Documentation

short __ast_alaw[256]

help

Definition at line 152 of file alaw.c.

unsigned char __ast_lin2a[8192]

converts signed linear to alaw

Definition at line 148 of file alaw.c.