/* http://www.slack.net/~ant/ */
#include "upsampler.h"
#include
#include
#include
/* Copyright (C) 2004-2007 Shay Green. This module is free software; you
can redistribute it and/or modify it under the terms of the GNU Lesser
General Public License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version. This
module 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 Lesser General Public License for more
details. You should have received a copy of the GNU Lesser General Public
License along with this module; if not, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */
#if INT_MAX < 0x7FFFFFFF
#error "Requires that int type have at least 32 bits"
#endif
enum { stereo = 2 };
enum { write_offset = 2 * stereo - stereo };
typedef short sample_t;
sample_t upsampler_buf [RESAMPLER_BUF_SIZE];
sample_t* upsampler_write_pos;
enum { shift = 15 };
enum { unit = 1 << shift };
static int s_step;
static int s_pos;
static int s_prev [2];
void upsampler_set_rate( int in_rate, int out_rate )
{
s_step = ((unsigned long) in_rate * unit + (unsigned) out_rate / 2) / out_rate;
if ( !upsampler_write_pos )
upsampler_clear();
}
void upsampler_clear( void )
{
s_pos = 0;
s_prev [0] = 0;
s_prev [1] = 0;
upsampler_write_pos = upsampler_buf + write_offset;
memset( upsampler_buf, 0, write_offset * sizeof upsampler_buf [0] );
}
int upsampler_read( sample_t* out_begin, int count )
{
/* restrict helps optimizer by telling it that input and output don't overlap,
allowing unrestricted reordering of memory loads and stores */
sample_t* restrict out = out_begin;
sample_t* const out_end = out + count;
sample_t const* restrict in = upsampler_buf;
sample_t* const in_end = upsampler_write_pos - write_offset;
if ( in < in_end )
{
/* local copies help optimizer */
int const step = s_step;
int prev0 = s_prev [0];
int prev1 = s_prev [1];
int pos = s_pos;
do
{
/* linear interpolation followed by two-point average */
#define INTERP( i, out )\
{\
int t = in [0 + i] * (unit - pos) + in [2 + i] * pos;\
out = (prev##i + t) >> (shift + 1);\
prev##i = t;\
}
/* interpolate left and right */
int out_0;
INTERP( 0, out_0 )
INTERP( 1, out [0] = out_0; out [1] )
out += stereo;
/* increment fractional position and separate whole part */
pos += step;
in += ((unsigned) pos >> shift) * stereo;
pos &= unit - 1;
}
while ( in < in_end && out < out_end );
s_prev [1] = prev1;
s_prev [0] = prev0;
s_pos = pos;
}
/* move unused samples to beginning of input buffer */
{
int result = out - out_begin;
int remain = upsampler_write_pos - in;
if ( remain < 0 )
remain = 0;
upsampler_write_pos = &upsampler_buf [remain];
memmove( upsampler_buf, in, remain * sizeof *in );
return result;
}
}