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https://github.com/ekeeke/Genesis-Plus-GX.git
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141 lines
4.3 KiB
C
141 lines
4.3 KiB
C
/* http://www.slack.net/~ant/ */
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#include "blip.h"
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#include <string.h>
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#include <stdlib.h>
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#include <stddef.h>
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/* Copyright (C) 2003-2008 Shay Green. This module is free software; you
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can redistribute it and/or modify it under the terms of the GNU Lesser
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General Public License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version. This
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module is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
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details. You should have received a copy of the GNU Lesser General Public
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License along with this module; if not, write to the Free Software Foundation,
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Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */
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enum { buf_extra = 2 }; /* extra samples to save past end */
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enum { time_bits = 16 }; /* bits in fraction of fixed-point sample counts */
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enum { time_unit = 1 << time_bits };
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enum { phase_bits = 15 }; /* bits in fraction of deltas in buffer */
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enum { phase_count = 1 << phase_bits };
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enum { phase_shift = time_bits - phase_bits };
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typedef int buf_t; /* type of element in delta buffer */
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struct blip_buffer_t
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{
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int factor; /* clocks to samples conversion factor */
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int offset; /* fractional position of clock 0 in delta buffer */
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int amp; /* current output amplitude (sum of all deltas up to now) */
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int size; /* size of delta buffer */
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buf_t buf [65536]; /* delta buffer, only size elements actually allocated */
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};
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blip_buffer_t* blip_alloc( double clock_rate, double sample_rate, int size )
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{
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/* Allocate space for structure and delta buffer */
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blip_buffer_t* s = (blip_buffer_t*) malloc(
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offsetof (blip_buffer_t, buf) + (size + buf_extra) * sizeof (buf_t) );
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if ( s != NULL )
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{
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/* Calculate output:input ratio and convert to fixed-point */
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double ratio = sample_rate / clock_rate;
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s->factor = (int) (ratio * time_unit + 0.5);
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s->size = size;
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blip_clear( s );
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}
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return s;
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}
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void blip_free( blip_buffer_t* s )
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{
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free( s );
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}
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void blip_clear( blip_buffer_t* s )
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{
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s->offset = 0;
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s->amp = 0;
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memset( s->buf, 0, (s->size + buf_extra) * sizeof (buf_t) );
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}
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void blip_add( blip_buffer_t* s, int clocks, int delta )
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{
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/* Convert to fixed-point time in terms of output samples */
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int fixed_time = clocks * s->factor + s->offset;
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/* Extract whole and fractional parts */
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int index = fixed_time >> time_bits; /* whole */
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int phase = fixed_time >> phase_shift & (phase_count - 1); /* fraction */
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/* Split delta between first and second samples */
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int second = delta * phase;
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int first = delta * phase_count - second;
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/* Add deltas to buffer */
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s->buf [index ] += first;
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s->buf [index+1] += second;
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}
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int blip_clocks_needed( const blip_buffer_t* s, int samples )
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{
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/* Fixed-point number of samples needed in addition to those in buffer */
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int fixed_needed = samples * time_unit - s->offset;
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/* If more are needed, convert to clocks and round up */
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return (fixed_needed <= 0) ? 0 : (fixed_needed - 1) / s->factor + 1;
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}
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void blip_end_frame( blip_buffer_t* s, int clocks )
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{
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s->offset += clocks * s->factor;
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}
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int blip_samples_avail( const blip_buffer_t* s )
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{
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return s->offset >> time_bits;
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}
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int blip_read_samples( blip_buffer_t* s, short out[], int stereo)
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{
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int count = s->offset >> time_bits;
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if ( count )
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{
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/* Sum deltas and write out */
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int i, sample;
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for ( i = 0; i < count; ++i )
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{
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/* Apply slight high-pass filter */
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s->amp -= s->amp >> 9;
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/* Add next delta */
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s->amp += s->buf [i];
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/* Calculate output sample */
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sample = s->amp >> phase_bits;
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/* Keep within 16-bit sample range */
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if ( sample < -32768 ) sample = -32768;
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if ( sample > +32767 ) sample = +32767;
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out [i << stereo] = sample;
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}
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/* Copy remaining samples to beginning of buffer and clear the rest */
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memmove( s->buf, &s->buf [count], buf_extra * sizeof (buf_t) );
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memset( &s->buf [buf_extra], 0, count * sizeof (buf_t) );
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/* Remove samples */
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s->offset -= count * time_unit;
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}
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return count;
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}
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