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122 lines
2.8 KiB
122 lines
2.8 KiB
/* A-law code from GStreamer
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* Copyright (C) 1999 Erik Walthinsen <omega@cse.ogi.edu>
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* PCM - A-Law conversion
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* Copyright (C) 2000 by Abramo Bagnara <abramo@alsa-project.org>
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Library General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Library General Public License for more details.
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*
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* You should have received a copy of the GNU Library General Public
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* License along with this library; if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 02111-1307, USA.
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*/
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#include "eth_ar/alaw.h"
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#include <stdint.h>
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static int16_t alaw_to_s16 (uint8_t a_val)
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{
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int t;
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int seg;
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a_val ^= 0x55;
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t = a_val & 0x7f;
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if (t < 16)
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t = (t << 4) + 8;
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else {
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seg = (t >> 4) & 0x07;
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t = ((t & 0x0f) << 4) + 0x108;
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t <<= seg - 1;
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}
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return ((a_val & 0x80) ? t : -t);
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}
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void alaw_decode(int16_t *samples, uint8_t *alaw, int nr)
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{
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int i;
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for (i = 0; i < nr; i++) {
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samples[i] = alaw_to_s16(alaw[i]);
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}
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}
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/*
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* s16_to_alaw() - Convert a 16-bit linear PCM value to 8-bit A-law
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*
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* s16_to_alaw() accepts an 16-bit integer and encodes it as A-law data.
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*
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* Linear Input Code Compressed Code
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* ------------------------ ---------------
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* 0000000wxyza 000wxyz
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* 0000001wxyza 001wxyz
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* 000001wxyzab 010wxyz
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* 00001wxyzabc 011wxyz
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* 0001wxyzabcd 100wxyz
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* 001wxyzabcde 101wxyz
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* 01wxyzabcdef 110wxyz
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* 1wxyzabcdefg 111wxyz
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*
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* For further information see John C. Bellamy's Digital Telephony, 1982,
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* John Wiley & Sons, pps 98-111 and 472-476.
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*/
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static int val_seg (int val)
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{
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int r = 1;
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val >>= 8;
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if (val & 0xf0) {
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val >>= 4;
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r += 4;
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}
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if (val & 0x0c) {
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val >>= 2;
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r += 2;
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}
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if (val & 0x02)
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r += 1;
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return r;
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}
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static uint8_t s16_to_alaw (int16_t pcm_val)
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{
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int seg;
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uint8_t mask;
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uint8_t aval;
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if (pcm_val >= 0) {
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mask = 0xD5;
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} else {
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mask = 0x55;
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pcm_val = -pcm_val;
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if (pcm_val > 0x7fff)
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pcm_val = 0x7fff;
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}
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if (pcm_val < 256)
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aval = pcm_val >> 4;
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else {
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/* Convert the scaled magnitude to segment number. */
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seg = val_seg (pcm_val);
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aval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0x0f);
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}
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return aval ^ mask;
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}
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void alaw_encode(uint8_t *alaw, int16_t *samples, int nr)
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{
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int i;
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for (i = 0; i < nr; i++) {
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alaw[i] = s16_to_alaw(samples[i]);
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}
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}
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