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();