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