warzone2100/lib/sequence/adpcm.c

100 lines
2.7 KiB
C

/*
This file is part of Warzone 2100.
Copyright (C) 1999-2004 Eidos Interactive
Copyright (C) 2005-2007 Warzone Resurrection Project
Warzone 2100 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.
Warzone 2100 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 Warzone 2100; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "adpcm.h"
char index_adjust[8] = { -1, -1, -1, -1, 2, 4, 6, 8 };
short step_size[89] = {
7, 8, 9, 10, 11, 12, 13, 14, 16, 17,
19, 21, 23, 25, 28, 31, 34, 37, 41, 45,
50, 55, 60, 66, 73, 80, 88, 97, 107, 118,
130, 143, 157, 173, 190, 209, 230, 253, 279, 307,
337, 371, 408, 449, 494, 544, 598, 658, 724, 796,
876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066,
2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358,
5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767
};
int pred_val = 0;
int step_idx = 0;
/* This code is "borrowed" from the ALSA library
http://www.alsa-project.org */
static short adpcm_decode_sample(char code) {
short pred_diff; /* Predicted difference to next sample */
short step; /* holds previous step_size value */
char sign;
int i;
/* Separate sign and magnitude */
sign = code & 0x8;
code &= 0x7;
/*
* Computes pred_diff = (code + 0.5) * step / 4,
* but see comment in adpcm_coder.
*/
step = step_size[step_idx];
/* Compute difference and new predicted value */
pred_diff = step >> 3;
for (i = 0x4; i; i >>= 1, step >>= 1) {
if (code & i) {
pred_diff += step;
}
}
pred_val += (sign) ? -pred_diff : pred_diff;
/* Clamp output value */
if (pred_val > 32767) {
pred_val = 32767;
} else if (pred_val < -32768) {
pred_val = -32768;
}
/* Find new step_size index value */
step_idx += index_adjust[(int) code];
if (step_idx < 0) {
step_idx = 0;
} else if (step_idx > 88) {
step_idx = 88;
}
return pred_val;
}
void adpcm_init(void) {
pred_val = 0;
step_idx = 0;
}
void adpcm_decode(unsigned char* input, unsigned int input_size, short** output) {
unsigned int i;
for (i = 0; i < input_size; ++i) {
unsigned char two_samples = input[i];
*((*output)++) = adpcm_decode_sample(two_samples >> 4);
*((*output)++) = adpcm_decode_sample(two_samples & 15);
}
}