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a few more instructions for today. abstract out conditional jump

This commit is contained in:
Matthew Laux 2022-07-18 23:35:51 -05:00
parent bc3f717285
commit 1b5f02ef7a
2 changed files with 33 additions and 12 deletions
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43
src/cpu.c
View File

@ -372,6 +372,16 @@ static void extended_insn(struct cpu *cpu, u8 insn)
}
}
static void conditional_jump(struct cpu *cpu, u8 opc, u8 neg_op, int flag) {
s8 target = (s8) read8(cpu, cpu->pc);
if ((opc == neg_op) ^ flag_isset(cpu, flag)) {
cpu->pc += target + 1;
cpu->cycle_count += instructions[opc].cycles_branch - instructions[opc].cycles;
} else {
cpu->pc++;
}
}
void cpu_step(struct cpu *cpu)
{
u8 temp;
@ -400,6 +410,9 @@ void cpu_step(struct cpu *cpu)
write16(cpu, read16(cpu, cpu->pc), cpu->sp);
cpu->pc += 2;
break;
case 0x09: // ADD HL,BC
add16(cpu, read_bc(cpu));
break;
case 0x19: // ADD HL,DE
add16(cpu, read_de(cpu));
break;
@ -545,17 +558,15 @@ void cpu_step(struct cpu *cpu)
break;
case 0x18: // JR r8
temp = read8(cpu, cpu->pc);
cpu->pc += *((signed char *) &temp) + 1;
cpu->pc += (s8) temp + 1;
break;
case 0x20: // JR NZ,r8
case 0x28: // JR Z,r8
temp = read8(cpu, cpu->pc);
if ((opc == 0x20) ^ flag_isset(cpu, FLAG_ZERO)) {
cpu->pc += *((signed char *) &temp) + 1;
cpu->cycle_count += instructions[opc].cycles_branch - instructions[opc].cycles;
} else {
cpu->pc++;
}
conditional_jump(cpu, opc, 0x20, FLAG_ZERO);
break;
case 0x30: // JR NC, i8
case 0x38: // JR C, i8
conditional_jump(cpu, opc, 0x30, FLAG_CARRY);
break;
case 0x21: // LD HL, d16
write_hl(cpu, read16(cpu, cpu->pc));
@ -621,6 +632,15 @@ void cpu_step(struct cpu *cpu)
case 0x8e: add(cpu, read8(cpu, read_hl(cpu)), 1); break;
case 0x8f: add(cpu, cpu->a, 1); break;
case 0xc6: // ADD A, u8
add(cpu, read8(cpu, cpu->pc), 0);
cpu->pc++;
break;
case 0xce: // ADC A, u8
add(cpu, read8(cpu, cpu->pc), 1);
cpu->pc++;
break;
case 0x90: subtract(cpu, cpu->b, 0, 0); break;
case 0x91: subtract(cpu, cpu->c, 0, 0); break;
case 0x92: subtract(cpu, cpu->d, 0, 0); break;
@ -691,6 +711,9 @@ void cpu_step(struct cpu *cpu)
case 0xf7: push(cpu, cpu->pc); cpu->pc = 0x30; break;
case 0xff: push(cpu, cpu->pc); cpu->pc = 0x38; break;
case 0x76: // HALT
break;
case 0xc1: // POP BC
write_bc(cpu, pop(cpu));
break;
@ -713,10 +736,6 @@ void cpu_step(struct cpu *cpu)
extended_insn(cpu, read8(cpu, cpu->pc));
cpu->pc++;
break;
case 0xce:
add(cpu, read8(cpu, cpu->pc), 1);
cpu->pc++;
break;
case 0xd1: // POP DE
write_de(cpu, pop(cpu));
break;

2
src/types.h
View File

@ -6,4 +6,6 @@ typedef unsigned short u16;
typedef unsigned long u32;
typedef unsigned long long u64;
typedef signed char s8;
#endif