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games/snes: SPC ADDW/SUBW fix

--- a/sys/src/games/snes/spc.c

+++ b/sys/src/games/snes/spc.c

@@ -581,6 +581,7 @@

 	case 0x79: cmp(spcread(sX|dp), spcread(sY|dp)); return 5;

 	case 0x7A:

 		b = memd16(azp());

+		sP &= ~SPCC;

 		sA = adc(sA, b);

 		sY = adc(sY, b >> 8);

 		if(sA != 0)

@@ -625,6 +626,7 @@

 	case 0x99: spcwrite(sX|dp, adc(spcread(sX|dp), spcread(sY|dp))); return 5;

 	case 0x9A:

 		b = memd16(azp());

+		sP |= SPCC;

 		sA = sbc(sA, b);

 		sY = sbc(sY, b >> 8);

 		if(sA != 0)