furnace/src/engine/blip_buf.c

/* blip_buf $vers. http://www.slack.net/~ant/ */

#include "blip_buf.h"

#include <assert.h>
#include <limits.h>
#include <string.h>
#include <stdlib.h>

/* Library Copyright (C) 2003-2009 Shay Green. This library 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
library 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 defined (BLARGG_TEST) && BLARGG_TEST
	#include "blargg_test.h"
#endif

/* Equivalent to ULONG_MAX >= 0xFFFFFFFF00000000.
Avoids constants that don't fit in 32 bits. */
#if ULONG_MAX/0xFFFFFFFF > 0xFFFFFFFF
	typedef unsigned long fixed_t;
	enum { pre_shift = 32 };

#elif defined(ULLONG_MAX)
	typedef unsigned long long fixed_t;
	enum { pre_shift = 32 };

#else
	typedef unsigned fixed_t;
	enum { pre_shift = 0 };

#endif

enum { time_bits = pre_shift + 20 };

static fixed_t const time_unit = (fixed_t) 1 << time_bits;

enum { bass_shift  = 9 }; /* affects high-pass filter breakpoint frequency */
enum { end_frame_extra = 2 }; /* allows deltas slightly after frame length */

enum { half_width  = 8 };
enum { buf_extra   = half_width*2 + end_frame_extra };
enum { phase_bits  = 5 };
enum { phase_count = 1 << phase_bits };
enum { delta_bits  = 15 };
enum { delta_unit  = 1 << delta_bits };
enum { frac_bits = time_bits - pre_shift };

/* We could eliminate avail and encode whole samples in offset, but that would
limit the total buffered samples to blip_max_frame. That could only be
increased by decreasing time_bits, which would reduce resample ratio accuracy.
*/

/** Sample buffer that resamples to output rate and accumulates samples
until they're read out */
struct blip_t
{
	fixed_t factor;
	fixed_t offset;
	int avail;
	int size;
	int integrator;
};

typedef int buf_t;

/* probably not totally portable */
#define SAMPLES( buf ) ((buf_t*) ((buf) + 1))

/* Arithmetic (sign-preserving) right shift */
#define ARITH_SHIFT( n, shift ) \
	((n) >> (shift))

enum { max_sample = +32767 };
enum { min_sample = -32768 };

#define CLAMP( n ) \
	{\
		if ( (short) n != n )\
			n = ARITH_SHIFT( n, 16 ) ^ max_sample;\
	}

static void check_assumptions( void )
{
	int n;
	
	#if INT_MAX < 0x7FFFFFFF || UINT_MAX < 0xFFFFFFFF
		#error "int must be at least 32 bits"
	#endif
	
	assert( (-3 >> 1) == -2 ); /* right shift must preserve sign */
	
	n = max_sample * 2;
	CLAMP( n );
	assert( n == max_sample );
	
	n = min_sample * 2;
	CLAMP( n );
	assert( n == min_sample );
	
	assert( blip_max_ratio <= time_unit );
	assert( blip_max_frame <= (fixed_t) -1 >> time_bits );
}

blip_t* blip_new( int size )
{
	blip_t* m;
	assert( size >= 0 );
	
	m = (blip_t*) malloc( sizeof *m + (size + buf_extra) * sizeof (buf_t) );
	if ( m )
	{
		m->factor = time_unit / blip_max_ratio;
		m->size   = size;
		blip_clear( m );
		check_assumptions();
	}
	return m;
}

void blip_delete( blip_t* m )
{
	if ( m != NULL )
	{
		/* Clear fields in case user tries to use after freeing */
		memset( m, 0, sizeof *m );
		free( m );
	}
}

void blip_set_rates( blip_t* m, double clock_rate, double sample_rate )
{
	double factor = time_unit * sample_rate / clock_rate;
	m->factor = (fixed_t) factor;
	
	/* Fails if clock_rate exceeds maximum, relative to sample_rate */
	assert( 0 <= factor - m->factor && factor - m->factor < 1 );
	
	/* Avoid requiring math.h. Equivalent to
	m->factor = (int) ceil( factor ) */
	if ( m->factor < factor )
		m->factor++;
	
	/* At this point, factor is most likely rounded up, but could still
	have been rounded down in the floating-point calculation. */
}

void blip_clear( blip_t* m )
{
	/* We could set offset to 0, factor/2, or factor-1. 0 is suitable if
	factor is rounded up. factor-1 is suitable if factor is rounded down.
	Since we don't know rounding direction, factor/2 accommodates either,
	with the slight loss of showing an error in half the time. Since for
	a 64-bit factor this is years, the halving isn't a problem. */
	
	m->offset     = m->factor / 2;
	m->avail      = 0;
	m->integrator = 0;
	memset( SAMPLES( m ), 0, (m->size + buf_extra) * sizeof (buf_t) );
}

int blip_clocks_needed( const blip_t* m, int samples )
{
	fixed_t needed;
	
	/* Fails if buffer can't hold that many more samples */
	assert( samples >= 0 && m->avail + samples <= m->size );
	
	needed = (fixed_t) samples * time_unit;
	if ( needed < m->offset )
		return 0;
	
	return (needed - m->offset + m->factor - 1) / m->factor;
}

void blip_end_frame( blip_t* m, unsigned t )
{
	fixed_t off = t * m->factor + m->offset;
	m->avail += off >> time_bits;
	m->offset = off & (time_unit - 1);
	
	/* Fails if buffer size was exceeded */
	assert( m->avail <= m->size );
}

int blip_samples_avail( const blip_t* m )
{
	return m->avail;
}

static void remove_samples( blip_t* m, int count )
{
	buf_t* buf = SAMPLES( m );
	int remain = m->avail + buf_extra - count;
	m->avail -= count;
	
	memmove( &buf [0], &buf [count], remain * sizeof buf [0] );
	memset( &buf [remain], 0, count * sizeof buf [0] );
}

int blip_read_samples( blip_t* m, short out [], int count, int stereo )
{
	assert( count >= 0 );
	
	if ( count > m->avail )
		count = m->avail;
	
	if ( count )
	{
		int const step = stereo ? 2 : 1;
		buf_t const* in  = SAMPLES( m );
		buf_t const* end = in + count;
		int sum = m->integrator;
		do
		{
			/* Eliminate fraction */
			int s = ARITH_SHIFT( sum, delta_bits );
			
			sum += *in++;
			
			CLAMP( s );
			
			*out = s;
			out += step;
			
			/* High-pass filter */
			sum -= s << (delta_bits - bass_shift);
		}
		while ( in != end );
		m->integrator = sum;
		
		remove_samples( m, count );
	}
	
	return count;
}

/* Things that didn't help performance on x86:
	__attribute__((aligned(128)))
	#define short int
	restrict
*/

/* Sinc_Generator( 0.9, 0.55, 4.5 ) */
static short const bl_step [phase_count + 1] [half_width] =
{
{   43, -115,  350, -488, 1136, -914, 5861,21022},
{   44, -118,  348, -473, 1076, -799, 5274,21001},
{   45, -121,  344, -454, 1011, -677, 4706,20936},
{   46, -122,  336, -431,  942, -549, 4156,20829},
{   47, -123,  327, -404,  868, -418, 3629,20679},
{   47, -122,  316, -375,  792, -285, 3124,20488},
{   47, -120,  303, -344,  714, -151, 2644,20256},
{   46, -117,  289, -310,  634,  -17, 2188,19985},
{   46, -114,  273, -275,  553,  117, 1758,19675},
{   44, -108,  255, -237,  471,  247, 1356,19327},
{   43, -103,  237, -199,  390,  373,  981,18944},
{   42,  -98,  218, -160,  310,  495,  633,18527},
{   40,  -91,  198, -121,  231,  611,  314,18078},
{   38,  -84,  178,  -81,  153,  722,   22,17599},
{   36,  -76,  157,  -43,   80,  824, -241,17092},
{   34,  -68,  135,   -3,    8,  919, -476,16558},
{   32,  -61,  115,   34,  -60, 1006, -683,16001},
{   29,  -52,   94,   70, -123, 1083, -862,15422},
{   27,  -44,   73,  106, -184, 1152,-1015,14824},
{   25,  -36,   53,  139, -239, 1211,-1142,14210},
{   22,  -27,   34,  170, -290, 1261,-1244,13582},
{   20,  -20,   16,  199, -335, 1301,-1322,12942},
{   18,  -12,   -3,  226, -375, 1331,-1376,12293},
{   15,   -4,  -19,  250, -410, 1351,-1408,11638},
{   13,    3,  -35,  272, -439, 1361,-1419,10979},
{   11,    9,  -49,  292, -464, 1362,-1410,10319},
{    9,   16,  -63,  309, -483, 1354,-1383, 9660},
{    7,   22,  -75,  322, -496, 1337,-1339, 9005},
{    6,   26,  -85,  333, -504, 1312,-1280, 8355},
{    4,   31,  -94,  341, -507, 1278,-1205, 7713},
{    3,   35, -102,  347, -506, 1238,-1119, 7082},
{    1,   40, -110,  350, -499, 1190,-1021, 6464},
{    0,   43, -115,  350, -488, 1136, -914, 5861}
};

/* Shifting by pre_shift allows calculation using unsigned int rather than
possibly-wider fixed_t. On 32-bit platforms, this is likely more efficient.
And by having pre_shift 32, a 32-bit platform can easily do the shift by
simply ignoring the low half. */

void blip_add_delta( blip_t* m, unsigned time, int delta )
{
	unsigned fixed = (unsigned) ((time * m->factor + m->offset) >> pre_shift);
	buf_t* out = SAMPLES( m ) + m->avail + (fixed >> frac_bits);
	
	int const phase_shift = frac_bits - phase_bits;
	int phase = fixed >> phase_shift & (phase_count - 1);
	short const* in  = bl_step [phase];
	short const* rev = bl_step [phase_count - phase];
	
	int interp = fixed >> (phase_shift - delta_bits) & (delta_unit - 1);
	int delta2 = (delta * interp) >> delta_bits;
	delta -= delta2;
	
	/* Fails if buffer size was exceeded */
	assert( out <= &SAMPLES( m ) [m->size + end_frame_extra] );
	
	out [0] += in[0]*delta + in[half_width+0]*delta2;
	out [1] += in[1]*delta + in[half_width+1]*delta2;
	out [2] += in[2]*delta + in[half_width+2]*delta2;
	out [3] += in[3]*delta + in[half_width+3]*delta2;
	out [4] += in[4]*delta + in[half_width+4]*delta2;
	out [5] += in[5]*delta + in[half_width+5]*delta2;
	out [6] += in[6]*delta + in[half_width+6]*delta2;
	out [7] += in[7]*delta + in[half_width+7]*delta2;
	
	in = rev;
	out [ 8] += in[7]*delta + in[7-half_width]*delta2;
	out [ 9] += in[6]*delta + in[6-half_width]*delta2;
	out [10] += in[5]*delta + in[5-half_width]*delta2;
	out [11] += in[4]*delta + in[4-half_width]*delta2;
	out [12] += in[3]*delta + in[3-half_width]*delta2;
	out [13] += in[2]*delta + in[2-half_width]*delta2;
	out [14] += in[1]*delta + in[1-half_width]*delta2;
	out [15] += in[0]*delta + in[0-half_width]*delta2;
}

void blip_add_delta_fast( blip_t* m, unsigned time, int delta )
{
	unsigned fixed = (unsigned) ((time * m->factor + m->offset) >> pre_shift);
	buf_t* out = SAMPLES( m ) + m->avail + (fixed >> frac_bits);
	
	int interp = fixed >> (frac_bits - delta_bits) & (delta_unit - 1);
	int delta2 = delta * interp;
	
	/* Fails if buffer size was exceeded */
	assert( out <= &SAMPLES( m ) [m->size + end_frame_extra] );
	
	out [7] += delta * delta_unit - delta2;
	out [8] += delta2;
}