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Lior Halphon
2025-07-17 22:49:38 +03:00
parent 5b17b41e07
commit b31cca77be
1 changed files with 36 additions and 27 deletions
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63
Core/apu.c
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@@ -6,46 +6,51 @@
#include <stdlib.h>
#include "gb.h"
/* Band limited synthesis based on: http://www.slack.net/~ant/bl-synth/ */
/* Band limited synthesis loosely based on: http://www.slack.net/~ant/bl-synth/ */
static int32_t band_limited_steps[GB_BAND_LIMITED_PHASES][GB_BAND_LIMITED_WIDTH];
static void __attribute__((constructor)) band_limited_init(void)
{
const unsigned master_size = GB_BAND_LIMITED_WIDTH * GB_BAND_LIMITED_PHASES + 1;
const unsigned master_size = GB_BAND_LIMITED_WIDTH * GB_BAND_LIMITED_PHASES;
double *master = malloc(master_size * sizeof(*master));
memset(master, 0, master_size * sizeof(*master));
const unsigned sine_size = (master_size - 1) * 2;
const unsigned max_harmonic = sine_size / 2 / GB_BAND_LIMITED_PHASES;
nounroll for (unsigned harmonic = 1; harmonic <= max_harmonic; harmonic += 2) {
double amplitude = 1.0 / harmonic / 2;
double to_angle = M_PI * 2 / sine_size * harmonic;
nounroll for (unsigned i = 0; i < master_size; i++) {
master[i] += sin(((signed)(i + 1) - (signed)sine_size / 4) * to_angle) * amplitude;
}
const double lowpass = 15.0 / 16.0; // 1.0 means using Nyquist as the exact cutoff
const double to_angle = M_PI / GB_BAND_LIMITED_PHASES * lowpass;
double sum = 0;
nounroll for (signed i = 0; i < master_size; i++) {
// Exact Blackman window
const double a0 = 7938 / 18608.0;
const double a1 = 9240 / 18608.0;
const double a2 = 1430 / 18608.0;
double window_angle = (2.0 * M_PI * i) / (master_size);
double window = a0 - a1 * cos(window_angle) + a2 * cos(2 * window_angle);
double angle = (i - (signed)master_size / 2) * to_angle;
sum += master[i] = (angle == 0? 1 : sin(angle) / angle) * window;
}
// Normalize master waveform
nounroll for (unsigned i = 0; i < master_size - 1; i++) {
master[i] += master[master_size - 1];
master[i] /= master[master_size - 1] * 2;
nounroll for (signed i = 0; i < master_size; i++) {
master[i] /= sum;
}
master[master_size - 1] = 1;
nounroll for (unsigned phase = 0; phase < GB_BAND_LIMITED_PHASES; phase++) {
nounroll for (signed phase = 0; phase < GB_BAND_LIMITED_PHASES; phase++) {
int32_t error = GB_BAND_LIMITED_ONE;
int32_t prev = 0;
nounroll for (unsigned i = 0; i < GB_BAND_LIMITED_WIDTH; i++) {
int32_t cur = master[(GB_BAND_LIMITED_PHASES - 1 - phase) + i * GB_BAND_LIMITED_PHASES] * GB_BAND_LIMITED_ONE;
int32_t delta = cur - prev;
error = error - delta;
prev = cur;
band_limited_steps[phase][i] = delta;
nounroll for (signed i = 0; i < GB_BAND_LIMITED_WIDTH; i++) {
double sum = 0;
nounroll for (signed j = 0; j < GB_BAND_LIMITED_PHASES; j++) {
signed index = i * GB_BAND_LIMITED_PHASES - phase + j;
if (index >= 0) {
sum += master[index];
}
}
int32_t cur = sum * GB_BAND_LIMITED_ONE;
error -= cur;
band_limited_steps[phase][i] = cur;
}
// Make sure the deltas sum to 1.0
band_limited_steps[phase][GB_BAND_LIMITED_WIDTH / 2 - 1] += error / 2;
band_limited_steps[phase][0] += error - (error / 2);
band_limited_steps[phase][GB_BAND_LIMITED_WIDTH / 2] += error;
}
free(master);
}
@@ -56,7 +61,9 @@ static void band_limited_update(GB_band_limited_t *band_limited, const GB_sample
unsigned delay = phase / GB_BAND_LIMITED_PHASES;
phase = phase & (GB_BAND_LIMITED_PHASES - 1);
GB_sample_t delta = {
struct {
signed left, right;
} delta = {
.left = input->left - band_limited->input.left,
.right = input->right - band_limited->input.right,
};
@@ -73,7 +80,9 @@ static void band_limited_update_unfiltered(GB_band_limited_t *band_limited, cons
{
if (input->packed == band_limited->input.packed) return;
GB_sample_t delta = {
struct {
signed left, right;
} delta = {
.left = input->left - band_limited->input.left,
.right = input->right - band_limited->input.right,
};