alaw.c

Go to the documentation of this file.

/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 1999 - 2005, Digium, Inc.
 *
 * Mark Spencer <[email protected]>
 *
 * 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 <[email protected]>
 */

/*** MODULEINFO
 <support_level>core</support_level>
 ***/

#include "asterisk.h"

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

}