Add addr_mode field, rely upon it vs. the opcode

This makes testing _slightly_ easier, because now the handlers require a
type of state in the cpu vs. a specific opcode state in the segment that
we execute from. (The latter being just more complex to work with and
require in testing.)

include/mos6502/mos6502.h

@@ -104,6 +104,11 @@ typedef struct {
      */
     vm_16bit eff_addr;
 
+    /*
+     * This is the address mode of the current execution.
+     */
+    int addr_mode;
+
     /*
      * These are the last opcode and last effective address that was
      * used in the instruction previous to the one currently being

src/mos6502/arith.c

@@ -154,19 +154,14 @@ DEFINE_INST(cpy)
  */
 DEFINE_INST(dec) 
 {
-    vm_8bit opcode = mos6502_get(cpu, cpu->PC);
-    bool is_acc = mos6502_addr_mode(opcode) == ACC;
-
-    if (!is_acc) {
-        MOS_CHECK_NZ(oper - 1);
-        mos6502_set(cpu, cpu->eff_addr, oper - 1);
+    if (cpu->addr_mode == ACC) {
+        MOS_CHECK_NZ(cpu->A - 1);
+        cpu->A--;
         return;
     }
 
-    // If we get here, then this is ACC mode, and we should work off
-    // that.
-    MOS_CHECK_NZ(cpu->A - 1);
-    cpu->A--;
+    MOS_CHECK_NZ(oper - 1);
+    mos6502_set(cpu, cpu->eff_addr, oper - 1);
 }
 
 /*
@@ -192,17 +187,14 @@ DEFINE_INST(dey)
  */
 DEFINE_INST(inc)
 {
-    vm_8bit opcode = mos6502_get(cpu, cpu->PC);
-    bool is_acc = mos6502_addr_mode(opcode) == ACC;
-
-    if (!is_acc) {
-        MOS_CHECK_NZ(oper + 1);
-        mos6502_set(cpu, cpu->eff_addr, oper + 1);
+    if (cpu->addr_mode == ACC) {
+        MOS_CHECK_NZ(cpu->A + 1);
+        cpu->A++;
         return;
     }
 
-    MOS_CHECK_NZ(cpu->A + 1);
-    cpu->A++;
+    MOS_CHECK_NZ(oper + 1);
+    mos6502_set(cpu, cpu->eff_addr, oper + 1);
 }
 
 /*

src/mos6502/bits.c

@@ -31,9 +31,6 @@ DEFINE_INST(and)
  */
 DEFINE_INST(asl)
 {
-    vm_8bit opcode = mos6502_get(cpu, cpu->PC);
-    bool is_acc = mos6502_addr_mode(opcode) == ACC;
-
     vm_8bit result = oper << 1;
 
     MOS_CHECK_NZ(result);
@@ -42,10 +39,10 @@ DEFINE_INST(asl)
         cpu->P |= MOS_CARRY;
     }
 
-    if (!is_acc) {
-        mos6502_set(cpu, cpu->eff_addr, result);
-    } else {
+    if (cpu->addr_mode == ACC) {
         cpu->A = result;
+    } else {
+        mos6502_set(cpu, cpu->eff_addr, result);
     }
 }
 
@@ -114,9 +111,6 @@ DEFINE_INST(eor)
  */
 DEFINE_INST(lsr)
 {
-    vm_8bit opcode = mos6502_get(cpu, cpu->PC);
-    bool is_acc = mos6502_addr_mode(opcode) == ACC;
-
     vm_8bit result = oper >> 1;
 
     // The N flag is ALWAYS cleared in LSR, because a zero is always
@@ -132,10 +126,10 @@ DEFINE_INST(lsr)
         cpu->P |= MOS_CARRY;
     }
 
-    if (!is_acc) {
-        mos6502_set(cpu, cpu->eff_addr, result);
-    } else {
+    if (cpu->addr_mode == ACC) {
         cpu->A = result;
+    } else {
+        mos6502_set(cpu, cpu->eff_addr, result);
     }
 }
 
@@ -156,9 +150,6 @@ DEFINE_INST(ora)
  */
 DEFINE_INST(rol)
 {
-    vm_8bit opcode = mos6502_get(cpu, cpu->PC);
-    bool is_acc = mos6502_addr_mode(opcode) == ACC;
-
     vm_8bit result = oper << 1;
 
     // Rotations are effectively _9-bit_. So we aren't rotating bit 7
@@ -175,10 +166,10 @@ DEFINE_INST(rol)
 
     MOS_CHECK_NZ(result);
 
-    if (!is_acc) {
-        mos6502_set(cpu, cpu->eff_addr, result);
-    } else {
+    if (cpu->addr_mode == ACC) {
         cpu->A = result;
+    } else {
+        mos6502_set(cpu, cpu->eff_addr, result);
     }
 }
 
@@ -188,9 +179,6 @@ DEFINE_INST(rol)
  */
 DEFINE_INST(ror)
 {
-    vm_8bit opcode = mos6502_get(cpu, cpu->PC);
-    bool is_acc = mos6502_addr_mode(opcode) == ACC;
-
     vm_8bit result = oper >> 1;
 
     // See the code for ROL for my note on 9-bit rotation (vs. 8-bit).
@@ -205,10 +193,10 @@ DEFINE_INST(ror)
 
     MOS_CHECK_NZ(result);
 
-    if (!is_acc) {
-        mos6502_set(cpu, cpu->eff_addr, result);
-    } else {
+    if (cpu->addr_mode == ACC) {
         cpu->A = result;
+    } else {
+        mos6502_set(cpu, cpu->eff_addr, result);
     }
 }
 

src/mos6502/mos6502.c

@@ -170,6 +170,7 @@ mos6502_create(vm_segment *rmem, vm_segment *wmem)
     mos6502_set_memory(cpu, rmem, wmem);
 
     cpu->eff_addr = 0;
+    cpu->addr_mode = 0;
     cpu->PC = 0;
     cpu->A = 0;
     cpu->X = 0;
@@ -303,16 +304,17 @@ mos6502_execute(mos6502 *cpu)
     mos6502_instruction_handler handler;
 
     opcode = mos6502_get(cpu, cpu->PC);
+    cpu->addr_mode = mos6502_addr_mode(opcode);
 
     // The disassembler knows how many bytes each operand requires
     // (maybe this code doesn't belong in the disassembler); let's use
     // that to figure out the total number of bytes to skip. We add 1
     // because we need to account for the opcode as well.
-    bytes = 1 + mos6502_dis_expected_bytes(mos6502_addr_mode(opcode));
+    bytes = 1 + mos6502_dis_expected_bytes(cpu->addr_mode);
 
     // First, we need to know how to resolve our effective address and
     // how to execute anything.
-    resolver = mos6502_get_address_resolver(mos6502_addr_mode(opcode));
+    resolver = mos6502_get_address_resolver(cpu->addr_mode);
     handler = mos6502_get_instruction_handler(opcode);
 
     // The operand is the effective operand, the value that the

tests/mos6502/arith.c

@@ -92,7 +92,7 @@ Test(mos6502_arith, cpy)
 Test(mos6502_arith, dec)
 {
     cpu->A = 5;
-    mos6502_set(cpu, cpu->PC, 0x3A);
+    cpu->addr_mode = ACC;
     mos6502_handle_dec(cpu, 0);
     cr_assert_eq(cpu->A, 4);
 
@@ -104,7 +104,7 @@ Test(mos6502_arith, dec)
     cpu->eff_addr = 123;
     mos6502_set(cpu, 123, 44);
 
-    mos6502_set(cpu, cpu->PC, 0x00);
+    cpu->addr_mode = 0;
     mos6502_handle_dec(cpu, 44);
     cr_assert_eq(mos6502_get(cpu, 123), 43);
 }
@@ -131,7 +131,7 @@ Test(mos6502_arith, inc)
 
     cpu->A = 8;
     cpu->eff_addr = 0;
-    mos6502_set(cpu, cpu->PC, 0x1A);
+    cpu->addr_mode = ACC;
     mos6502_handle_inc(cpu, 0);
     cr_assert_eq(cpu->A, 9);
 

tests/mos6502/bits.c

@@ -23,7 +23,7 @@ Test(mos6502_bits, asl)
     mos6502_handle_asl(cpu, 22);
     cr_assert_eq(mos6502_get(cpu, 123), 44);
 
-    mos6502_set(cpu, cpu->PC, 0x0A);
+    cpu->addr_mode = ACC;
     mos6502_handle_asl(cpu, 5);
     cr_assert_eq(cpu->A, 10);
 
@@ -98,7 +98,7 @@ Test(mos6502_bits, lsr)
     cr_assert_eq(mos6502_get(cpu, 123), 5);
     cr_assert_eq(cpu->P & MOS_CARRY, MOS_CARRY);
 
-    mos6502_set(cpu, cpu->PC, 0x4A);
+    cpu->addr_mode = ACC;
     mos6502_handle_lsr(cpu, 5);
     cr_assert_eq(cpu->A, 2);
     cr_assert_eq(cpu->P & MOS_CARRY, MOS_CARRY);
@@ -122,7 +122,7 @@ Test(mos6502_bits, rol)
     mos6502_handle_rol(cpu, 128);
     cr_assert_eq(mos6502_get(cpu, 234), 0);
 
-    mos6502_set(cpu, cpu->PC, 0x2A);
+    cpu->addr_mode = ACC;
     cpu->P = 0;
     cpu->A = 0xff;
     mos6502_handle_rol(cpu, cpu->A);
@@ -141,7 +141,7 @@ Test(mos6502_bits, ror)
     mos6502_handle_ror(cpu, 0);
     cr_assert_eq(mos6502_get(cpu, 123), 128);
 
-    mos6502_set(cpu, cpu->PC, 0x6A);
+    cpu->addr_mode = ACC;
     cpu->P = 0;
     cpu->A = 0xff;
     mos6502_handle_ror(cpu, cpu->A);