mirror of https://github.com/xemu-project/xemu.git
91 lines
2.7 KiB
C
91 lines
2.7 KiB
C
/*
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* ADPCM decoder
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*
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* Copyright (c) 2017 Jannik Vogel
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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 Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 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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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, see <http://www.gnu.org/licenses/>.
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*/
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// See https://wiki.multimedia.cx/index.php/IMA_ADPCM for more information
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#include <stdint.h>
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#include <assert.h>
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static int8_t ima_index_table[16] = {
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-1, -1, -1, -1, 2, 4, 6, 8,
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-1, -1, -1, -1, 2, 4, 6, 8
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};
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static uint16_t ima_step_table[89] = {
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7, 8, 9, 10, 11, 12, 13, 14, 16, 17,
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19, 21, 23, 25, 28, 31, 34, 37, 41, 45,
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50, 55, 60, 66, 73, 80, 88, 97, 107, 118,
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130, 143, 157, 173, 190, 209, 230, 253, 279, 307,
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337, 371, 408, 449, 494, 544, 598, 658, 724, 796,
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876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066,
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2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358,
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5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
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15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767
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};
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typedef struct {
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int32_t predictor;
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int8_t step_index;
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uint16_t step;
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} ADPCMDecoder;
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static void adpcm_decoder_initialize(ADPCMDecoder* d, int16_t predictor, int8_t step_index) {
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d->predictor = predictor;
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d->step_index = step_index;
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}
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// The upper portion of the `nibble` argument is ignored.
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static int16_t adpcm_decoder_step(ADPCMDecoder* d, uint8_t nibble) {
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// Get step and prepare index for next sample
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if (d->step_index < 0) {
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d->step_index = 0;
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} else if (d->step_index > 88) {
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d->step_index = 88;
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}
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d->step = ima_step_table[d->step_index];
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d->step_index += ima_index_table[nibble & 0xF];
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// Calculate diff
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int32_t diff = d->step >> 3;
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if (nibble & 1) {
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diff += d->step >> 2;
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}
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if (nibble & 2) {
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diff += d->step >> 1;
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}
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if (nibble & 4) {
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diff += d->step;
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}
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if (nibble & 8) {
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diff = -diff;
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}
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// Update predictor and clamp to signed 16 bit
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d->predictor += diff;
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if (d->predictor < -0x8000) {
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d->predictor = -0x8000;
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} else if (d->predictor > 0x7FFF) {
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d->predictor = 0x7FFF;
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}
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return d->predictor;
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}
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