{
int i;
DATATYPE *buf = (DATATYPE *)buffer;
struct SN76496 *R = &sn[chip];
/* If the volume is 0, increase the counter */
for (i = 0;i < 4;i++)
{
if (R->Volume[i] == 0)
{
/* note that I do count += length, NOT count = length + 1. You might think */
/* it's the same since the volume is 0, but doing the latter could cause */
/* interferencies when the program is rapidly modulating the volume. */
if (R->Count[i] <= length*STEP) R->Count[i] += length*STEP;
}
}
while (length > 0)
{
int vol[4];
unsigned int out;
int left;
/* vol[] keeps track of how long each square wave stays */
/* in the 1 position during the sample period. */
vol[0] = vol[1] = vol[2] = vol[3] = 0;
for (i = 0;i < 3;i++)
{
if (R->Output[i]) vol[i] += R->Count[i];
R->Count[i] -= STEP;
/* Period[i] is the half period of the square wave. Here, in each */
/* loop I add Period[i] twice, so that at the end of the loop the */
/* square wave is in the same status (0 or 1) it was at the start. */
/* vol[i] is also incremented by Period[i], since the wave has been 1 */
/* exactly half of the time, regardless of the initial position. */
/* If we exit the loop in the middle, Output[i] has to be inverted */
/* and vol[i] incremented only if the exit status of the square */
/* wave is 1. */
while (R->Count[i] <= 0)
{
R->Count[i] += R->Period[i];
if (R->Count[i] > 0)
{
R->Output[i] ^= 1;
if (R->Output[i]) vol[i] += R->Period[i];
break;
}
R->Count[i] += R->Period[i];
vol[i] += R->Period[i];
}
if (R->Output[i]) vol[i] -= R->Count[i];
}
left = STEP;
do
{
int nextevent;
if (R->Count[3] < left) nextevent = R->Count[3];
else nextevent = left;
if (R->Output[3]) vol[3] += R->Count[3];
R->Count[3] -= nextevent;
if (R->Count[3] <= 0)
{
if (R->RNG & 1) R->RNG ^= R->NoiseFB;
R->RNG >>= 1;
R->Output[3] = R->RNG & 1;
R->Count[3] += R->Period[3];
if (R->Output[3]) vol[3] += R->Period[3];
}
if (R->Output[3]) vol[3] -= R->Count[3];
left -= nextevent;
} while (left > 0);
out = vol[0] * R->Volume[0] + vol[1] * R->Volume[1] +
vol[2] * R->Volume[2] + vol[3] * R->Volume[3];
if (out > MAX_OUTPUT * STEP) out = MAX_OUTPUT * STEP;
*(buf++) = DATACONV(out);
length--;
}
}