Implement indirect zero-page addressing mode

Author: Scitoshi Nakayobro

functions.h

@@ -21,6 +21,10 @@ static inline size_t mem_indexed_indirect(cpu *m, uint8_t addr, uint8_t off) {
     return mem_abs(m->mem[addr+off], m->mem[addr+off+1], 0);
 }
 
+static inline size_t mem_indirect_zp(cpu *m, uint8_t addr) {
+    return mem_abs(m->mem[addr], m->mem[addr + 1], 0);
+}
+
 // set arg MUST be 16 bits, not 8, so that add results can fit into set.
 static inline void set_flag(cpu *m, uint8_t flag, uint16_t set) {
     if (set) {

opcode_handlers/arithmetic.h

@@ -36,6 +36,10 @@ case ADC_ZPX:
     add(m, m->mem[ZP(NEXT_BYTE(m) + m->x)]);
     break;
 
+case ADC_INZP:
+    add(m, m->mem[mem_indirect_zp(m, NEXT_BYTE(m))]);
+    break;
+
 case SBC_AB:
     arg1 = NEXT_BYTE(m);
     arg2 = NEXT_BYTE(m);
@@ -73,3 +77,7 @@ case SBC_ZP:
 case SBC_ZPX:
     sub(m, m->mem[ZP(NEXT_BYTE(m) + m->x)]);
     break;
+
+case SBC_INZP:
+    sub(m, m->mem[mem_indirect_zp(m, NEXT_BYTE(m))]);
+    break;

opcode_handlers/compare.h

@@ -36,6 +36,10 @@ case CMP_ZPX:
     cmp(m, m->mem[ZP(NEXT_BYTE(m) + m->x)], m->ac);
     break;
 
+case CMP_INZP:
+    cmp(m, m->mem[mem_indirect_zp(m, NEXT_BYTE(m))], m->ac);
+    break;
+
 case CPX_AB:
     arg1 = NEXT_BYTE(m);
     arg2 = NEXT_BYTE(m);

opcode_handlers/load.h

@@ -44,6 +44,10 @@ case LDA_ZPX:
     set_flags(m, m->ac);
     break;
 
+case LDA_INZP:
+    m->ac = m->mem[mem_indirect_zp(m, NEXT_BYTE(m))];
+    break;
+
 case LDX_AB:
     arg1 = NEXT_BYTE(m);
     arg2 = NEXT_BYTE(m);

opcode_handlers/logical.h

@@ -44,6 +44,11 @@ case AND_INY:
     set_flags(m, m->ac);
     break;
 
+case AND_INZP:
+    m->ac &= m->mem[mem_indirect_zp(m, NEXT_BYTE(m))];
+    set_flags(m, m->ac);
+    break;
+
 case EOR_IMM:
     m->ac ^= NEXT_BYTE(m);
     set_flags(m, m->ac);
@@ -90,6 +95,11 @@ case EOR_INY:
     set_flags(m, m->ac);
     break;
 
+case EOR_INZP:
+    m->ac ^= m->mem[mem_indirect_zp(m, NEXT_BYTE(m))];
+    set_flags(m, m->ac);
+    break;
+
 case ORA_IMM:
     m->ac |= NEXT_BYTE(m);
     set_flags(m, m->ac);
@@ -136,6 +146,11 @@ case ORA_INY:
     set_flags(m, m->ac);
     break;
 
+case ORA_INZP:
+    m->ac |= m->mem[mem_indirect_zp(m, NEXT_BYTE(m))];
+    set_flags(m, m->ac);
+    break;
+
 case BIT_AB:
     arg1 = NEXT_BYTE(m);
     arg2 = NEXT_BYTE(m);

opcode_handlers/store.h

@@ -46,6 +46,12 @@ case STA_ZPX:
     mark_dirty(m, r1);
     break;
 
+case STA_INZP:
+    r1 = mem_indirect_zp(m, NEXT_BYTE(m));
+    m->mem[r1] = m->ac;
+    mark_dirty(m, r1);
+    break;
+
 case STX_ZP:
     r1 = ZP(NEXT_BYTE(m));
     m->mem[r1] = m->x;