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/*
* PCM - A-Law conversion
* Copyright (c) 2000 by Abramo Bagnara <abramo@alsa-project.org>
*
* Wrapper for linphone Codec class by Simon Morlat <simon.morlat@linphone.org>
*
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
static inline int val_seg(int val)
{
int r = 0;
val >>= 7; /*7 = 4 + 3*/
if (val & 0xf0) {
val >>= 4;
r += 4;
}
if (val & 0x0c) {
val >>= 2;
r += 2;
}
if (val & 0x02)
r += 1;
return r;
}
/*
* s16_to_alaw() - Convert a 16-bit linear PCM value to 8-bit A-law
*
* s16_to_alaw() accepts an 16-bit integer and encodes it as A-law data.
*
* Linear Input Code Compressed Code
* ------------------------ ---------------
* 0000000wxyza 000wxyz
* 0000001wxyza 001wxyz
* 000001wxyzab 010wxyz
* 00001wxyzabc 011wxyz
* 0001wxyzabcd 100wxyz
* 001wxyzabcde 101wxyz
* 01wxyzabcdef 110wxyz
* 1wxyzabcdefg 111wxyz
*
* For further information see John C. Bellamy's Digital Telephony, 1982,
* John Wiley & Sons, pps 98-111 and 472-476.
* G711 is designed for 13 bits input signal, this function add extra shifting to take this into account.
*/
static inline unsigned char s16_to_alaw(int pcm_val)
{
int mask;
int seg;
unsigned char aval;
if (pcm_val >= 0) {
mask = 0xD5;
} else {
mask = 0x55;
pcm_val = -pcm_val;
if (pcm_val > 0x7fff)
pcm_val = 0x7fff;
}
if (pcm_val < 256) /*256 = 32 << 3*/
aval = pcm_val >> 4; /*4 = 1 + 3*/
else {
/* Convert the scaled magnitude to segment number. */
seg = val_seg(pcm_val);
aval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0x0f);
}
return aval ^ mask;
}
/*
* alaw_to_s16() - Convert an A-law value to 16-bit linear PCM
*
*/
static inline int alaw_to_s16(unsigned char a_val)
{
int t;
int seg;
a_val ^= 0x55;
t = a_val & 0x7f;
if (t < 16)
t = (t << 4) + 8;
else {
seg = (t >> 4) & 0x07;
t = ((t & 0x0f) << 4) + 0x108;
t <<= seg -1;
}
return ((a_val & 0x80) ? t : -t);
}
/*
* s16_to_ulaw() - Convert a linear PCM value to u-law
*
* In order to simplify the encoding process, the original linear magnitude
* is biased by adding 33 which shifts the encoding range from (0 - 8158) to
* (33 - 8191). The result can be seen in the following encoding table:
*
* Biased Linear Input Code Compressed Code
* ------------------------ ---------------
* 00000001wxyza 000wxyz
* 0000001wxyzab 001wxyz
* 000001wxyzabc 010wxyz
* 00001wxyzabcd 011wxyz
* 0001wxyzabcde 100wxyz
* 001wxyzabcdef 101wxyz
* 01wxyzabcdefg 110wxyz
* 1wxyzabcdefgh 111wxyz
*
* Each biased linear code has a leading 1 which identifies the segment
* number. The value of the segment number is equal to 7 minus the number
* of leading 0's. The quantization interval is directly available as the
* four bits wxyz. * The trailing bits (a - h) are ignored.
*
* Ordinarily the complement of the resulting code word is used for
* transmission, and so the code word is complemented before it is returned.
*
* For further information see John C. Bellamy's Digital Telephony, 1982,
* John Wiley & Sons, pps 98-111 and 472-476.
*/
static inline unsigned char s16_to_ulaw(int pcm_val) /* 2's complement (16-bit range) */
{
int mask;
int seg;
unsigned char uval;
if (pcm_val < 0) {
pcm_val = 0x84 - pcm_val;
mask = 0x7f;
} else {
pcm_val += 0x84;
mask = 0xff;
}
if (pcm_val > 0x7fff)
pcm_val = 0x7fff;
/* Convert the scaled magnitude to segment number. */
seg = val_seg(pcm_val);
/*
* Combine the sign, segment, quantization bits;
* and complement the code word.
*/
uval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0x0f);
return uval ^ mask;
}
/*
* ulaw_to_s16() - Convert a u-law value to 16-bit linear PCM
*
* First, a biased linear code is derived from the code word. An unbiased
* output can then be obtained by subtracting 33 from the biased code.
*
* Note that this function expects to be passed the complement of the
* original code word. This is in keeping with ISDN conventions.
*/
static inline int ulaw_to_s16(unsigned char u_val)
{
int t;
/* Complement to obtain normal u-law value. */
u_val = ~u_val;
/*
* Extract and bias the quantization bits. Then
* shift up by the segment number and subtract out the bias.
*/
t = ((u_val & 0x0f) << 3) + 0x84;
t <<= (u_val & 0x70) >> 4;
return ((u_val & 0x80) ? (0x84 - t) : (t - 0x84));
}
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