love2d.megasource/libs/openal-soft/OpenAL32/Include/bs2b.h

/*-
 * Copyright (c) 2005 Boris Mikhaylov
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#ifndef BS2B_H
#define BS2B_H

/* Number of crossfeed levels */
#define BS2B_CLEVELS           3

/* Normal crossfeed levels */
#define BS2B_HIGH_CLEVEL       3
#define BS2B_MIDDLE_CLEVEL     2
#define BS2B_LOW_CLEVEL        1

/* Easy crossfeed levels */
#define BS2B_HIGH_ECLEVEL      BS2B_HIGH_CLEVEL    + BS2B_CLEVELS
#define BS2B_MIDDLE_ECLEVEL    BS2B_MIDDLE_CLEVEL  + BS2B_CLEVELS
#define BS2B_LOW_ECLEVEL       BS2B_LOW_CLEVEL     + BS2B_CLEVELS

/* Default crossfeed levels */
#define BS2B_DEFAULT_CLEVEL    BS2B_HIGH_ECLEVEL
/* Default sample rate (Hz) */
#define BS2B_DEFAULT_SRATE     44100

#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */

struct bs2b {
    int level;  /* Crossfeed level */
    int srate;   /* Sample rate (Hz) */

    /* Lowpass IIR filter coefficients */
    float a0_lo;
    float b1_lo;

    /* Highboost IIR filter coefficients */
    float a0_hi;
    float a1_hi;
    float b1_hi;

    /* Buffer of last filtered sample.
     * [0] - first channel, [1] - second channel
     */
    struct t_last_sample {
        float asis[2];
        float lo[2];
        float hi[2];
    } last_sample;
};

/* Clear buffers and set new coefficients with new crossfeed level and sample
 * rate values.
 * level - crossfeed level of *LEVEL values.
 * srate - sample rate by Hz.
 */
void bs2b_set_params(struct bs2b *bs2b, int level, int srate);

/* Return current crossfeed level value */
int bs2b_get_level(struct bs2b *bs2b);

/* Return current sample rate value */
int bs2b_get_srate(struct bs2b *bs2b);

/* Clear buffer */
void bs2b_clear(struct bs2b *bs2b);

/* Crossfeeds one stereo sample that are pointed by sample.
 * [0] - first channel, [1] - second channel.
 * Returns crossfided sample by sample pointer.
 */
inline void bs2b_cross_feed(struct bs2b *bs2b, float *restrict sample)
{
/* Single pole IIR filter.
 * O[n] = a0*I[n] + a1*I[n-1] + b1*O[n-1]
 */

/* Lowpass filter */
#define lo_filter(in, out_1) (bs2b->a0_lo*(in) + bs2b->b1_lo*(out_1))

/* Highboost filter */
#define hi_filter(in, in_1, out_1) (bs2b->a0_hi*(in) + bs2b->a1_hi*(in_1) + bs2b->b1_hi*(out_1))

    /* Lowpass filter */
    bs2b->last_sample.lo[0] = lo_filter(sample[0], bs2b->last_sample.lo[0]);
    bs2b->last_sample.lo[1] = lo_filter(sample[1], bs2b->last_sample.lo[1]);

    /* Highboost filter */
    bs2b->last_sample.hi[0] = hi_filter(sample[0], bs2b->last_sample.asis[0], bs2b->last_sample.hi[0]);
    bs2b->last_sample.hi[1] = hi_filter(sample[1], bs2b->last_sample.asis[1], bs2b->last_sample.hi[1]);
    bs2b->last_sample.asis[0] = sample[0];
    bs2b->last_sample.asis[1] = sample[1];

    /* Crossfeed */
    sample[0] = bs2b->last_sample.hi[0] + bs2b->last_sample.lo[1];
    sample[1] = bs2b->last_sample.hi[1] + bs2b->last_sample.lo[0];
#undef hi_filter
#undef lo_filter
} /* bs2b_cross_feed */

#ifdef __cplusplus
}    /* extern "C" */
#endif /* __cplusplus */

#endif /* BS2B_H */