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This patch solves problem 1 in 8126; it should not slow down the alaw codec, but should prevent signal degradation via multiple trips thru the codec. Fossil estimates the twice thru this codec will prevent fax from working. 4-6 times thru would result hearable, noticeable, voice degradation.

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git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@80166 65c4cc65-6c06-0410-ace0-fbb531ad65f3
This commit is contained in:
Steve Murphy
2007-08-21 16:36:34 +00:00
parent db1f93048f
commit 4b5a9ae533
3 changed files with 100 additions and 2 deletions
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50
include/asterisk/alaw.h
View File

@@ -23,21 +23,69 @@
#ifndef _ASTERISK_ALAW_H
#define _ASTERISK_ALAW_H
#define G711_FAST_AND_DIRTY 1
/* #define G711_REDUCED_BRANCHING */
/*! Init the ulaw conversion stuff */
/*!
* To init the ulaw to slinear conversion stuff, this needs to be run.
*/
void ast_alaw_init(void);
#define AST_ALAW_BIT_LOSS 4
#define AST_ALAW_STEP (1 << AST_ALAW_BIT_LOSS)
#define AST_ALAW_TAB_SIZE (32768 / AST_ALAW_STEP + 1)
#define AST_ALAW_SIGN_BIT 0x80
#define AST_ALAW_AMI_MASK 0x55
/*! converts signed linear to mulaw */
/*!
*/
*/
#ifdef G711_FAST_AND_DIRTY
extern unsigned char __ast_lin2a[8192];
#else
extern unsigned char __ast_lin2a[AST_ALAW_TAB_SIZE];
#endif
/*! help */
extern short __ast_alaw[256];
#ifdef G711_FAST_AND_DIRTY
#define AST_LIN2A(a) (__ast_lin2a[((unsigned short)(a)) >> 3])
#else
#define AST_LIN2A_LOOKUP(mag) \
__ast_lin2a[(mag) >> AST_ALAW_BIT_LOSS]
/*! convert signed linear sample to sign-magnitude pair for a-Law */
static inline void ast_alaw_get_sign_mag(short sample, unsigned *sign, unsigned *mag)
{
/* It may look illogical to retrive the sign this way in both cases,
* but this helps gcc eliminate the branch below and produces
* faster code */
*sign = ((unsigned short)sample >> 8) & AST_ALAW_SIGN_BIT;
#if defined(G711_REDUCED_BRANCHING)
{
unsigned dual_mag = (-sample << 16) | (unsigned short)sample;
*mag = (dual_mag >> (*sign >> 3)) & 0xffffU;
}
#else
if (sample < 0)
*mag = -sample;
else
*mag = sample;
#endif /* G711_REDUCED_BRANCHING */
*sign ^= AST_ALAW_SIGN_BIT;
}
static inline unsigned char AST_LIN2A(short sample)
{
unsigned mag, sign;
ast_alaw_get_sign_mag(sample, &sign, &mag);
return (sign | AST_LIN2A_LOOKUP(mag)) ^ AST_ALAW_AMI_MASK;
}
#endif
#define AST_ALAW(a) (__ast_alaw[(int)(a)])
#endif /* _ASTERISK_ALAW_H */

50
include/asterisk/ulaw.h
View File

@@ -23,21 +23,71 @@
#ifndef _ASTERISK_ULAW_H
#define _ASTERISK_ULAW_H
#define G711_FAST_AND_DIRTY 1
/* #define G711_REDUCED_BRANCHING */
/*! Init the ulaw conversion stuff */
/*!
* To init the ulaw to slinear conversion stuff, this needs to be run.
*/
void ast_ulaw_init(void);
#define AST_ULAW_BIT_LOSS 3
#define AST_ULAW_STEP (1 << AST_ULAW_BIT_LOSS)
#define AST_ULAW_TAB_SIZE (32768 / AST_ULAW_STEP + 1)
#define AST_ULAW_SIGN_BIT 0x80
/*! converts signed linear to mulaw */
/*!
*/
#ifdef G711_FAST_AND_DIRTY
extern unsigned char __ast_lin2mu[16384];
#else
extern unsigned char __ast_lin2mu[AST_ULAW_TAB_SIZE];
#endif
/*! help */
extern short __ast_mulaw[256];
#ifdef G711_FAST_AND_DIRTY
#define AST_LIN2MU(a) (__ast_lin2mu[((unsigned short)(a)) >> 2])
#else
#define AST_LIN2MU_LOOKUP(mag) \
__ast_lin2mu[((mag) + AST_ULAW_STEP / 2) >> AST_ULAW_BIT_LOSS]
/*! convert signed linear sample to sign-magnitude pair for u-Law */
static inline void ast_ulaw_get_sign_mag(short sample, unsigned *sign, unsigned *mag)
{
/* It may look illogical to retrive the sign this way in both cases,
* but this helps gcc eliminate the branch below and produces
* faster code */
*sign = ((unsigned short)sample >> 8) & AST_ULAW_SIGN_BIT;
#if defined(G711_REDUCED_BRANCHING)
{
unsigned dual_mag = (-sample << 16) | (unsigned short)sample;
*mag = (dual_mag >> (*sign >> 3)) & 0xffffU;
}
#else
if (sample < 0)
*mag = -sample;
else
*mag = sample;
#endif /* G711_REDUCED_BRANCHING */
}
static inline unsigned char AST_LIN2MU(short sample)
{
unsigned mag, sign;
ast_ulaw_get_sign_mag(sample, &sign, &mag);
return ~(sign | AST_LIN2MU_LOOKUP(mag));
}
#endif
#define AST_MULAW(a) (__ast_mulaw[(a)])
#endif /* _ASTERISK_ULAW_H */

2
main/alaw.c
View File

@@ -71,7 +71,7 @@ static inline short int alaw2linear (unsigned char alaw)
int seg;
alaw ^= AMI_MASK;
i = ((alaw & 0x0F) << 4);
i = ((alaw & 0x0F) << 4) + 8 /* rounding error */;
seg = (((int) alaw & 0x70) >> 4);
if (seg)
i = (i + 0x100) << (seg - 1);