From 8e314467806e311e3a5838d16190684f0c06fdc0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jo=C3=A3o=20Magalh=C3=A3es?= <joamag@gmail.com>
Date: Wed, 29 Jun 2022 10:35:17 +0100
Subject: [PATCH] feat: new cp operation
---
src/cpu.rs | 26 ++++++++++++++++++++++++--
1 file changed, 24 insertions(+), 2 deletions(-)
diff --git a/src/cpu.rs b/src/cpu.rs
index e9da5993..84ea6bdc 100644
--- a/src/cpu.rs
+++ b/src/cpu.rs
@@ -273,7 +273,7 @@ pub const INSTRUCTIONS: [(fn(&mut Cpu), u8, &'static str); 256] = [
(nop, 4, "! UNIMP !"),
(nop, 4, "! UNIMP !"),
(nop, 4, "! UNIMP !"),
- (nop, 4, "! UNIMP !"),
+ (cp_a_u8, 8, "CP A, u8"),
(nop, 4, "! UNIMP !"),
];
@@ -879,6 +879,11 @@ fn ld_mff00c_a(cpu: &mut Cpu) {
cpu.mmu.write(0xff0c + cpu.c as u16, cpu.a);
}
+fn cp_a_u8(cpu: &mut Cpu) {
+ let byte = cpu.read_u8();
+ sub_set_flags(cpu, cpu.a, byte);
+}
+
fn rl_c(cpu: &mut Cpu) {
cpu.c = rl(cpu, cpu.c);
}
@@ -916,13 +921,30 @@ fn bit_h(cpu: &mut Cpu, bit: u8) {
cpu.set_half_carry(true);
}
+fn sub_set_flags(cpu: &mut Cpu, x: u8, y: u8) -> u8 {
+ // Check for borrow using 32bit arithmetics
+ let x = x as u32;
+ let y = y as u32;
+
+ let value = x.wrapping_sub(y);
+
+ let value_b = value as u8;
+
+ cpu.set_sub(true);
+ cpu.set_carry(value & 0x100 == 0x100);
+ cpu.set_zero(value_b == 0);
+ cpu.set_half_carry((x ^ y ^ value) & 0x10 == 0x10);
+
+ value_b
+}
+
fn add_u16_u16(cpu: &mut Cpu, first: u16, second: u16) -> u16 {
let first = first as u32;
let second = second as u32;
let value = first.wrapping_add(second);
cpu.set_sub(false);
- cpu.set_carry(value & 0x1000 == 0x1000);
+ cpu.set_carry(value & 0x10000 == 0x10000);
cpu.set_half_carry((first ^ second ^ value) & 0x1000 == 0x1000);
value as u16
--
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