move addressing mode parsing into separate function

1 files changed, 44 insertions, 73 deletions

diff --git a/cpu.c b/cpu.c
index 08c6119..86fbcb0 100644
--- a/cpu.c
+++ b/cpu.c
@@ -62,49 +62,58 @@ peek16(uint16_t addr)
 	return (uint16_t)memory[addr] | ((uint16_t)memory[addr + 1] << 8);
 }
 
-void
-adc(enum addressing_mode mode)
+uint8_t
+opmode_arg(enum addressing_mode mode)
 {
 	uint8_t arg, val;
-	uint16_t sum;	// 16-bit sum makes it easier to determine carry flag
 
 	if (mode != AM_ABS && mode != AM_ABS_X && mode != AM_ABS_Y)
 		arg = peek(regs.pc++);
 	else
-		arg = peek16(regs.pc++);
+		arg = peek16(regs.pc), regs.pc += 2;
 
 	switch (mode) {
-	case AM_IMM:	/* $69 */
+	case AM_IMM:
 		val = arg;
 		break;
-	case AM_ZP:	/* $65 */
+	case AM_ZP:
 		val = peek(arg % 256);
 		break;
-	case AM_ABS:	/* $6D */
-		val = peek16(arg);
-		break;
-	case AM_ZP_X:	/* $75 */
+	case AM_ZP_X:
 		val = peek((arg + regs.x) % 256);
 		break;
-	case AM_ABS_X:	/* $7D */
+	case AM_ZP_Y:
+		val = peek((arg + regs.y) % 256);
+		break;
+	case AM_ABS:
+		val = peek16(arg);
+		break;
+	case AM_ABS_X:
 		val = peek16(arg + regs.x);
 		break;
-	case AM_ABS_Y:	/* $79 */
+	case AM_ABS_Y:
 		val = peek16(arg + regs.y);
 		break;
-	case AM_IND_X:	/* $61 */
+	case AM_IND_X:
 		val = peek(peek((arg + regs.x) % 256) + peek((arg + regs.x + 1) % 256) * 256);
 		break;
-	case AM_IND_Y:	/* $71 */
+	case AM_IND_Y:
 		val = peek(peek(arg) + peek((arg + 1) % 256) * 256 + regs.y);
 		break;
 	default:
-		fprintf(stderr, "INVALID ADC ADDRESSING MODE\n");
+		fprintf(stderr, "INVALID ADDRESSING MODE\n");
 		abort();
-		return;
 	}
 
-	sum = regs.a + val + regs.status.carry;
+	return val;
+}
+
+void
+adc(uint8_t arg)
+{
+	uint16_t sum;	// 16-bit sum makes it easier to determine carry flag
+
+	sum = regs.a + arg + regs.status.carry;
 	regs.a = sum & 0xFF;
 
 	regs.status.carry = sum > 0xFF;
@@ -144,48 +153,10 @@ inx(void)
 }
 
 void
-lda(enum addressing_mode mode)
+lda(uint8_t arg)
 {
-	uint8_t arg, val;
-
-	if (mode != AM_ABS && mode != AM_ABS_X && mode != AM_ABS_Y)
-		arg = peek(regs.pc++);
-	else
-		arg = peek16(regs.pc++);
-
-	switch (mode) {
-	case AM_IMM:	/* $A9 */
-		val = arg;
-		break;
-	case AM_ZP:	/* $A5 */
-		val = peek(arg % 256);
-		break;
-	case AM_ABS:	/* $AD */
-		val = peek16(arg);
-		break;
-	case AM_ZP_X:	/* $B5 */
-		val = peek((arg + regs.x) % 256);
-		break;
-	case AM_ABS_X:	/* $BD */
-		val = peek16(arg + regs.x);
-		break;
-	case AM_ABS_Y:	/* $B9 */
-		val = peek16(arg + regs.y);
-		break;
-	case AM_IND_X:	/* $A1 */
-		val = peek(peek((arg + regs.x) % 256) + peek((arg + regs.x + 1) % 256) * 256);
-		break;
-	case AM_IND_Y:	/* $B1 */
-		val = peek(peek(arg) + peek((arg + 1) % 256) * 256 + regs.y);
-		break;
-	default:
-		fprintf(stderr, "INVALID LDA ADDRESSING MODE\n");
-		abort();
-		return;
-	}
-
 	printf("arg1 $%02X\n", arg);
-	regs.a = val;
+	regs.a = arg;
 
 	STATUS_UPDATE_ZERO(regs.a);
 	STATUS_UPDATE_NEGATIVE(regs.a);
@@ -206,55 +177,55 @@ interpret(void)
 			brk();
 			return;
 		case 0x61:
-			adc(AM_IND_X);
+			adc(opmode_arg(AM_IND_X));
 			break;
 		case 0x65:
-			adc(AM_ZP);
+			adc(opmode_arg(AM_ZP));
 			break;
 		case 0x69:
-			adc(AM_IMM);
+			adc(opmode_arg(AM_IMM));
 			break;
 		case 0x6D:
-			adc(AM_ABS);
+			adc(opmode_arg(AM_ABS));
 			break;
 		case 0x71:
-			adc(AM_IND_Y);
+			adc(opmode_arg(AM_IND_Y));
 			break;
 		case 0x75:
-			adc(AM_ZP_X);
+			adc(opmode_arg(AM_ZP_X));
 			break;
 		case 0x79:
-			adc(AM_ABS_Y);
+			adc(opmode_arg(AM_ABS_Y));
 			break;
 		case 0x7D:
-			adc(AM_ABS_X);
+			adc(opmode_arg(AM_ABS_X));
 			break;
 		case 0xa1:
-			lda(AM_IND_X);
+			lda(opmode_arg(AM_IND_X));
 			break;
 		case 0xa5:
-			lda(AM_ZP);
+			lda(opmode_arg(AM_ZP));
 			break;
 		case 0xa9:
-			lda(AM_IMM);
+			lda(opmode_arg(AM_IMM));
 			break;
 		case 0xaa:
 			tax();
 			break;
 		case 0xad:
-			lda(AM_ABS);
+			lda(opmode_arg(AM_ABS));
 			break;
 		case 0xb1:
-			lda(AM_IND_Y);
+			lda(opmode_arg(AM_IND_Y));
 			break;
 		case 0xb5:
-			lda(AM_ZP_X);
+			lda(opmode_arg(AM_ZP_X));
 			break;
 		case 0xb9:
-			lda(AM_ABS_Y);
+			lda(opmode_arg(AM_ABS_Y));
 			break;
 		case 0xbd:
-			lda(AM_ABS_X);
+			lda(opmode_arg(AM_ABS_X));
 			break;
 		case 0xe8:
 			inx();