ref: e847abfa04ca6dc058810a4b31cec6ee5d91f94e
dir: /src/helpers/fir_resampler.c/
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include "internal/fir_resampler.h"
enum { fir_width = 16 };
enum { fir_max_res = 1024 };
enum { fir_min_width = (fir_width < 4 ? 4 : fir_width) };
enum { fir_adj_width = fir_min_width / 4 * 4 + 2 };
enum { fir_stereo = 1 }; /* channel count, not boolean value */
enum { fir_write_offset = fir_adj_width * fir_stereo };
enum { fir_buffer_size = fir_width * 2 };
typedef short fir_impulse[fir_adj_width];
/* exp slope to 31/32 of ln(8) */
static const double fir_ratios[32] = {
1.000, 1.067, 1.139, 1.215, 1.297, 1.384, 1.477, 1.576,
1.682, 1.795, 1.915, 2.044, 2.181, 2.327, 2.484, 2.650,
2.828, 3.018, 3.221, 3.437, 3.668, 3.914, 4.177, 4.458,
4.757, 5.076, 5.417, 5.781, 6.169, 6.583, 7.025, 7.497
};
static fir_impulse fir_impulses[32][fir_max_res];
#undef PI
#define PI 3.1415926535897932384626433832795029
static void gen_sinc( double rolloff, int width, double offset, double spacing, double scale,
int count, short* out )
{
double const maxh = 256;
double const step = PI / maxh * spacing;
double const to_w = maxh * 2 / width;
double const pow_a_n = pow( rolloff, maxh );
double angle = (count / 2 - 1 + offset) * -step;
scale /= maxh * 2;
while ( count-- )
{
double w;
*out++ = 0;
w = angle * to_w;
if ( fabs( w ) < PI )
{
double rolloff_cos_a = rolloff * cos( angle );
double num = 1 - rolloff_cos_a -
pow_a_n * cos( maxh * angle ) +
pow_a_n * rolloff * cos( (maxh - 1) * angle );
double den = 1 - rolloff_cos_a - rolloff_cos_a + rolloff * rolloff;
double sinc = scale * num / den - scale;
out [-1] = (short) (cos( w ) * sinc + sinc);
}
angle += step;
}
}
typedef struct fir_resampler
{
int write_pos, write_filled;
int read_pos, read_filled;
unsigned short phase;
unsigned int phase_inc;
unsigned int ratio_set;
int buffer_in[fir_buffer_size * 2];
int buffer_out[fir_buffer_size];
} fir_resampler;
void * fir_resampler_create()
{
fir_resampler * r = ( fir_resampler * ) malloc( sizeof(fir_resampler) );
if ( !r ) return 0;
r->write_pos = 0;
r->write_filled = 0;
r->read_pos = 0;
r->read_filled = 0;
r->phase = 0;
r->phase_inc = 0;
r->ratio_set = 0;
memset( r->buffer_in, 0, sizeof(r->buffer_in) );
memset( r->buffer_out, 0, sizeof(r->buffer_out) );
return r;
}
void fir_resampler_delete(void * _r)
{
free( _r );
}
void * fir_resampler_dup(void * _r)
{
fir_resampler * r_in = ( fir_resampler * ) _r;
fir_resampler * r_out = ( fir_resampler * ) malloc( sizeof(fir_resampler) );
if ( !r_out ) return 0;
r_out->write_pos = r_in->write_pos;
r_out->write_filled = r_in->write_filled;
r_out->read_pos = r_in->read_pos;
r_out->read_filled = r_in->read_filled;
r_out->phase = r_in->phase;
r_out->phase_inc = r_in->phase_inc;
r_out->ratio_set = r_in->ratio_set;
memcpy( r_out->buffer_in, r_in->buffer_in, sizeof(r_in->buffer_in) );
memcpy( r_out->buffer_out, r_in->buffer_out, sizeof(r_in->buffer_out) );
return r_out;
}
int fir_resampler_get_free_count(void *_r)
{
fir_resampler * r = ( fir_resampler * ) _r;
return fir_buffer_size - r->write_filled;
}
int fir_resampler_ready(void *_r)
{
fir_resampler * r = ( fir_resampler * ) _r;
return r->write_filled > fir_adj_width;
}
void fir_resampler_clear(void *_r)
{
fir_resampler * r = ( fir_resampler * ) _r;
r->write_pos = 0;
r->write_filled = 0;
r->read_pos = 0;
r->read_filled = 0;
r->phase = 0;
memset( r->buffer_in, 0, sizeof(r->buffer_in) );
}
void fir_resampler_set_rate(void *_r, double new_factor)
{
fir_resampler * r = ( fir_resampler * ) _r;
r->phase_inc = (int)( new_factor * 65536.0 );
r->ratio_set = 0;
while ( r->ratio_set < 31 && new_factor > fir_ratios[ r->ratio_set ] ) r->ratio_set++;
}
void fir_resampler_write_sample(void *_r, short s)
{
fir_resampler * r = ( fir_resampler * ) _r;
if ( r->write_filled < fir_buffer_size )
{
int s32 = s;
r->buffer_in[ r->write_pos ] = s32;
r->buffer_in[ r->write_pos + fir_buffer_size ] = s32;
++r->write_filled;
r->write_pos = ( r->write_pos + 1 ) % fir_buffer_size;
}
}
void fir_init()
{
double const rolloff = 0.999;
double const gain = 1.0;
int const res = fir_max_res;
int i;
for (i = 0; i < 32; i++)
{
double const ratio_ = fir_ratios[ i ];
double fraction = 1.0 / (double)fir_max_res;
double const filter = (ratio_ < 1.0) ? 1.0 : 1.0 / ratio_;
double pos = 0.0;
short* out = (short*) fir_impulses[ i ];
int n;
for ( n = res; --n >= 0; )
{
gen_sinc( rolloff, (int) (fir_adj_width * filter + 1) & ~1, pos, filter,
(double) (0x7FFF * gain * filter), (int) fir_adj_width, out );
out += fir_adj_width;
pos += fraction;
}
}
}
int fir_resampler_run(void *_r, int ** out_, int * out_end)
{
fir_resampler * r = ( fir_resampler * ) _r;
int in_size = r->write_filled;
int const* in_ = r->buffer_in + fir_buffer_size + r->write_pos - r->write_filled;
int used = 0;
in_size -= fir_write_offset;
if ( in_size > 0 )
{
int* out = *out_;
int const* in = in_;
int const* const in_end = in + in_size;
int phase = r->phase;
int phase_inc = r->phase_inc;
int ratio_set = r->ratio_set;
do
{
// accumulate in extended precision
short const* imp = fir_impulses[ratio_set][(phase & 0xFFC0) >> 6];
int pt = imp [0];
int s = pt * in [0];
int n;
if ( out >= out_end )
break;
for ( n = (fir_adj_width - 2) / 2; n; --n )
{
pt = imp [1];
s += pt * in [1];
// pre-increment more efficient on some RISC processors
imp += 2;
pt = imp [0];
in += 2;
s += pt * in [0];
}
pt = imp [1];
s += pt * in [1];
phase += phase_inc;
in += (phase >> 16) - fir_adj_width + 2;
phase &= 65535;
*out++ = (int) (s >> 7);
}
while ( in < in_end );
r->phase = phase;
*out_ = out;
used = in - in_;
r->write_filled -= used;
}
return used;
}
int fir_resampler_get_sample(void *_r)
{
fir_resampler * r = ( fir_resampler * ) _r;
if ( r->read_filled < 1 )
{
int write_pos = ( r->read_pos + r->read_filled ) % fir_buffer_size;
int write_size = fir_buffer_size - write_pos;
int * out = r->buffer_out + write_pos;
if ( write_size > ( fir_buffer_size - r->read_filled ) )
write_size = fir_buffer_size - r->read_filled;
fir_resampler_run( r, &out, out + write_size );
r->read_filled += out - r->buffer_out - write_pos;
}
if ( r->read_filled < 1 )
return 0;
return r->buffer_out[ r->read_pos ];
}
void fir_resampler_remove_sample(void *_r)
{
fir_resampler * r = ( fir_resampler * ) _r;
if ( r->read_filled > 0 )
{
--r->read_filled;
r->read_pos = ( r->read_pos + 1 ) % fir_buffer_size;
}
}