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AUDIO: Use fixed-point arithmetic in the CMS emulator

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This commit is contained in:
Cameron Cawley 2022-11-19 13:04:51 +00:00 committed by Eugene Sandulenko
parent e494ef1aa8
commit 8c40151285
2 changed files with 17 additions and 16 deletions
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25
audio/softsynth/cms.cpp
View File

@ -30,8 +30,9 @@
#define LEFT 0x00
#define RIGHT 0x01
#define FRAC_ONE_CMS (1UL << 8)
/*#define MASTER_CLOCK 14318180/2 */
#define MASTER_CLOCK 7159090
#define MASTER_CLOCK (7159090UL * FRAC_ONE_CMS)
static const byte envelope[8][64] = {
/* zero amplitude */
@ -166,9 +167,9 @@ void CMSEmulator::update(int chip, int16 *buffer, int length) {
for (ch = 0; ch < 2; ch++) {
switch (saa->noise_params[ch]) {
case 0: saa->noise[ch].freq = MASTER_CLOCK/256 * 2; break;
case 1: saa->noise[ch].freq = MASTER_CLOCK/512 * 2; break;
case 2: saa->noise[ch].freq = MASTER_CLOCK/1024 * 2; break;
case 0: saa->noise[ch].freq = (MASTER_CLOCK * 2) / 256; break;
case 1: saa->noise[ch].freq = (MASTER_CLOCK * 2) / 512; break;
case 2: saa->noise[ch].freq = (MASTER_CLOCK * 2) / 1024; break;
case 3: saa->noise[ch].freq = saa->channels[ch * 3].freq; break;
default: break;
}
@ -180,18 +181,18 @@ void CMSEmulator::update(int chip, int16 *buffer, int length) {
/* for each channel */
for (ch = 0; ch < 6; ch++) {
if (saa->channels[ch].freq == 0.0)
saa->channels[ch].freq = (double)((2 * MASTER_CLOCK/512) << saa->channels[ch].octave) /
(511.0 - (double)saa->channels[ch].frequency);
if (saa->channels[ch].freq == 0)
saa->channels[ch].freq = (((2 * MASTER_CLOCK) / 512) << saa->channels[ch].octave) /
(511 - saa->channels[ch].frequency);
/* check the actual position in the square wave */
saa->channels[ch].counter -= saa->channels[ch].freq;
while (saa->channels[ch].counter < 0) {
/* calculate new frequency now after the half wave is updated */
saa->channels[ch].freq = (double)((2 * MASTER_CLOCK/512) << saa->channels[ch].octave) /
(511.0 - (double)saa->channels[ch].frequency);
saa->channels[ch].freq = (((2 * MASTER_CLOCK) / 512) << saa->channels[ch].octave) /
(511 - saa->channels[ch].frequency);
saa->channels[ch].counter += _sampleRate;
saa->channels[ch].counter += _sampleRate * FRAC_ONE_CMS;
saa->channels[ch].level ^= 1;
/* eventually clock the envelope counters */
@ -225,7 +226,7 @@ void CMSEmulator::update(int chip, int16 *buffer, int length) {
/* check the actual position in noise generator */
saa->noise[ch].counter -= saa->noise[ch].freq;
while (saa->noise[ch].counter < 0) {
saa->noise[ch].counter += _sampleRate;
saa->noise[ch].counter += _sampleRate * FRAC_ONE_CMS;
if (((saa->noise[ch].level & 0x4000) == 0) == ((saa->noise[ch].level & 0x0040) == 0) )
saa->noise[ch].level = (saa->noise[ch].level << 1) | 1;
else
@ -336,7 +337,7 @@ void CMSEmulator::portWriteIntern(int chip, int offset, int data) {
/* Synch & Reset generators */
for (i = 0; i < 6; i++) {
saa->channels[i].level = 0;
saa->channels[i].counter = 0.0;
saa->channels[i].counter = 0;
}
}
break;

8
audio/softsynth/cms.h
View File

@ -34,16 +34,16 @@ struct saa1099_channel {
int envelope[2]; /* envelope (0x00..0x0f or 0x10 == off) */
/* vars to simulate the square wave */
double counter;
double freq;
int32 counter;
int32 freq;
int level;
};
/* this structure defines a noise channel */
struct saa1099_noise {
/* vars to simulate the noise generator output */
double counter;
double freq;
int32 counter;
int32 freq;
int level; /* noise polynomal shifter */
};