PSG Emulator Code

[Yazwho]

I was looking through the emulators code to see how the PSG works.

Even with my pretty terrible C knowledge, I understand most of it. Apart from the section below. I think I understand the syntax (xor the volume with $20, if the 6th bit ($20) is set, or the volume with $C0), I dont get why it's doing it. It kinda feels like it's meant to cap the value at 63, but it doesn't do that and there are surly better ways to achieve it anyway. So I was wondering if anyone else knew?

https://github.com/commanderx16/x16-emulator/blob/master/src/vera_psg.c

	int8_t sv = (v ^ 0x20);
	if (sv & 0x20) {
	sv |= 0xC0;
	}

[Yazwho]

Ah, so I had a problem with my sheet as I was trying to visualise this. Its rebasing the volume.

Given its an unsigned int8, surly you could just -32?

Anyway, all makes sense now.

[ZeroByte]

actually, int8_t is signed. What the line "sv |= 0xc0;" does is fill in the 2 msb with 1s if the resultant value is negative.