cog/Frameworks/GME/gme/Fir_Resampler.h

187 lines
4.3 KiB
C++

// Finite impulse response (FIR) resampler with adjustable FIR size
// Game_Music_Emu https://bitbucket.org/mpyne/game-music-emu/
#ifndef FIR_RESAMPLER_H
#define FIR_RESAMPLER_H
#include "blargg_common.h"
#include <string.h>
class Fir_Resampler_ {
public:
// Use Fir_Resampler<width> (below)
// Set input/output resampling ratio and optionally low-pass rolloff and gain.
// Returns actual ratio used (rounded to internal precision).
double time_ratio( double factor, double rolloff = 0.999, double gain = 1.0 );
// Current input/output ratio
double ratio() const { return ratio_; }
// Input
typedef short sample_t;
// Resize and clear input buffer
blargg_err_t buffer_size( int );
// Clear input buffer. At least two output samples will be available after
// two input samples are written.
void clear();
// Number of input samples that can be written
int max_write() const { return buf.end() - write_pos; }
// Pointer to place to write input samples
sample_t* buffer() { return write_pos; }
// Notify resampler that 'count' input samples have been written
void write( long count );
// Number of input samples in buffer
int written() const { return write_pos - &buf [write_offset]; }
// Skip 'count' input samples. Returns number of samples actually skipped.
int skip_input( long count );
// Output
// Number of extra input samples needed until 'count' output samples are available
int input_needed( blargg_long count ) const;
// Number of output samples available
int avail() const { return avail_( write_pos - &buf [width_ * stereo] ); }
public:
~Fir_Resampler_();
protected:
enum { stereo = 2 };
enum { max_res = 32 };
blargg_vector<sample_t> buf;
sample_t* write_pos;
int res;
int imp_phase;
int const width_;
int const write_offset;
blargg_ulong skip_bits;
int step;
int input_per_cycle;
double ratio_;
sample_t* impulses;
Fir_Resampler_( int width, sample_t* );
int avail_( blargg_long input_count ) const;
};
// Width is number of points in FIR. Must be even and 4 or more. More points give
// better quality and rolloff effectiveness, and take longer to calculate.
template<int width>
class Fir_Resampler : public Fir_Resampler_ {
static_assert( width >= 4 && width % 2 == 0, "FIR width must be even and have 4 or more points" );
short impulses [max_res] [width];
public:
Fir_Resampler() : Fir_Resampler_( width, impulses [0] ) { }
// Read at most 'count' samples. Returns number of samples actually read.
typedef short sample_t;
int read( sample_t* out, blargg_long count );
};
// End of public interface
inline void Fir_Resampler_::write( long count )
{
write_pos += count;
assert( write_pos <= buf.end() );
}
template<int width>
int Fir_Resampler<width>::read( sample_t* out_begin, blargg_long count )
{
sample_t* out = out_begin;
const sample_t* in = buf.begin();
sample_t* end_pos = write_pos;
blargg_ulong skip = skip_bits >> imp_phase;
sample_t const* imp = impulses [imp_phase];
int remain = res - imp_phase;
int const step = this->step;
count >>= 1;
// Resampling can add noise so don't actually do it if we've matched sample
// rate
const double ratio1 = ratio() - 1.0;
const bool should_resample =
( ratio1 >= 0 ? ratio1 : -ratio1 ) >= 0.00001;
if ( end_pos - in >= width * stereo )
{
end_pos -= width * stereo;
do
{
count--;
if ( count < 0 )
break;
if( !should_resample )
{
out [0] = static_cast<sample_t>( in [0] );
out [1] = static_cast<sample_t>( in [1] );
}
else
{
// accumulate in extended precision
blargg_long l = 0;
blargg_long r = 0;
const sample_t* i = in;
for ( int n = width / 2; n; --n )
{
int pt0 = imp [0];
l += pt0 * i [0];
r += pt0 * i [1];
int pt1 = imp [1];
imp += 2;
l += pt1 * i [2];
r += pt1 * i [3];
i += 4;
}
remain--;
l >>= 15;
r >>= 15;
in += (skip * stereo) & stereo;
skip >>= 1;
if ( !remain )
{
imp = impulses [0];
skip = skip_bits;
remain = res;
}
out [0] = (sample_t) l;
out [1] = (sample_t) r;
}
in += step;
out += 2;
}
while ( in <= end_pos );
}
imp_phase = res - remain;
int left = write_pos - in;
write_pos = &buf [left];
memmove( buf.begin(), in, left * sizeof *in );
return out - out_begin;
}
#endif