cpu: fix up register accesses

The HL dereference operations cause problems indexing into the
registers array, because it causes a hole in the array that only
exists in the 8-bit register space.

Instead of accessing the registers directly by the same indices used
in in the assembly instructions, create a lookup table to map between
them.

Signed-off-by: Max Regan <mgregan2@gmail.com>

src/cpu.c

@@ -382,30 +382,52 @@ static lr35902_instr lr35902_cb_instrs[] = {
 	/*0xF?*/ set, set,
 };
 
+static int cpu_reg16_to_idx[NUM_LR35902_REGS_16] = {
+	[LR35902_REG_BC] = 0,
+	[LR35902_REG_DE] = 1,
+	[LR35902_REG_HL] = 2,
+	[LR35902_REG_AF] = 3,
+	[LR35902_REG_PC] = 4,
+	[LR35902_REG_SP] = 5,
+};
+
 uint16_t lr35902_get_reg_16(struct lr35902_state *cpu, lr35902_regs_16 reg)
 {
-	ASSERT(reg >= 0);
-	ASSERT_MSG(reg < NUM_LR35902_REGS_16, "reg=%d\n", reg);
-	return cpu->regs_16[reg];
+	ASSERT_MSG(reg >= 0 && reg < NUM_LR35902_REGS_16, "reg=%d\n", reg);
+	return cpu->regs_16[cpu_reg16_to_idx[reg]];
 }
 
+static int cpu_reg8_to_idx[NUM_LR35902_REGS_8] = {
+	[LR35902_REG_A] = 6,
+	[LR35902_REG_B] = 0,
+	[LR35902_REG_C] = 1,
+	[LR35902_REG_D] = 2,
+	[LR35902_REG_E] = 3,
+	[LR35902_REG_H] = 4,
+	[LR35902_REG_L] = 5,
+	[LR35902_REG_F] = 7,
+	[LR35902_REG_HL_DEREF] = -1,
+};
+
 uint8_t lr35902_get_reg_8(struct lr35902_state *cpu, lr35902_regs_8 reg)
 {
+	ASSERT(reg < NUM_LR35902_REGS_8);
 	ASSERT(reg != LR35902_REG_HL_DEREF);
-	return cpu->regs_8[reg];
+	return cpu->regs_8[cpu_reg8_to_idx[reg]];
 }
 
 void lr35902_set_reg_16(struct lr35902_state *cpu, lr35902_regs_16 reg,
                         uint16_t val)
 {
-	cpu->regs_16[reg] = val;
+	ASSERT(reg < NUM_LR35902_REGS_16 && reg >= 0);
+	cpu->regs_16[cpu_reg16_to_idx[reg]] = val;
 }
 
 void lr35902_set_reg_8(struct lr35902_state *cpu, lr35902_regs_8 reg,
                        uint8_t val)
 {
-	ASSERT(reg < NUM_LR35902_REGS_8);
-	cpu->regs_8[reg] = val;
+	ASSERT(reg < NUM_LR35902_REGS_8 && reg >= 0);
+	cpu->regs_8[cpu_reg8_to_idx[reg]] = val;
 }
 
 
@@ -534,15 +556,17 @@ static uint8_t _get_reg_8(struct lr35902_state *cpu, uint8_t reg){
 	if (reg == LR35902_REG_HL_DEREF){
 		return cpu->mem_read(cpu, lr35902_get_reg_16(cpu, LR35902_REG_HL));
 	} else {
-		return cpu->regs_8[reg];
+		return cpu->regs_8[cpu_reg8_to_idx[reg]];
 	}
 }
 
 static void _set_reg_8(struct lr35902_state *cpu, uint8_t reg, uint8_t val){
+	ASSERT(reg < NUM_LR35902_REGS_8 && reg >= 0);
+
 	if (reg == LR35902_REG_HL_DEREF){
 		cpu->mem_write(cpu, lr35902_get_reg_16(cpu, LR35902_REG_HL), val);
 	} else {
-		cpu->regs_8[reg] = val;
+		cpu->regs_8[cpu_reg8_to_idx[reg]] = val;
 	}
 }
 

src/cpu.h

@@ -15,10 +15,10 @@
 #define LR35902_MAX_EVENTS 16
 
 typedef enum {
-	LR35902_REG_AF= 0,
-	LR35902_REG_BC,
-	LR35902_REG_DE,
-	LR35902_REG_HL,
+	LR35902_REG_BC = 0,
+	LR35902_REG_DE = 1,
+	LR35902_REG_HL = 2,
+	LR35902_REG_AF = 3,
 	LR35902_REG_SP,
 	LR35902_REG_PC,
 	NUM_LR35902_REGS_16