From 5fbc661f5c5bc45e945c2c95729fe2b6783e5ac8 Mon Sep 17 00:00:00 2001
From: Alex Janka <alex@alexjanka.com>
Date: Fri, 24 Feb 2023 17:10:44 +1100
Subject: [PATCH] SO CLOSE

---
 src/main.rs                                |  8 +++++++-
 src/processor/instructions/instructions.rs | 14 ++++++-------
 src/processor/instructions/primitives.rs   | 23 ++++++++--------------
 src/processor/opcodes.rs                   |  4 ++--
 4 files changed, 24 insertions(+), 25 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 949b788..5a59a66 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,4 +1,10 @@
-#![feature(exclusive_range_pattern, let_chains, slice_flatten, async_closure)]
+#![feature(
+    exclusive_range_pattern,
+    let_chains,
+    slice_flatten,
+    async_closure,
+    bigint_helper_methods
+)]
 
 mod constants;
 mod processor;
diff --git a/src/processor/instructions/instructions.rs b/src/processor/instructions/instructions.rs
index 356665c..b39e8bc 100644
--- a/src/processor/instructions/instructions.rs
+++ b/src/processor/instructions/instructions.rs
@@ -32,25 +32,25 @@ impl Cpu {
     }
 
     pub(crate) fn cp(&mut self, first: u8, second: u8) {
-        self.sub_u8s(first, second);
+        self.sub_u8s(first, second, false);
     }
 
     pub(crate) fn add(&mut self, first: u8, second: u8) -> u8 {
-        self.add_u8s(first, second)
+        self.add_u8s(first, second, false)
     }
 
     pub(crate) fn adc(&mut self, first: u8, second: u8) -> u8 {
-        let val = second.wrapping_add(self.get_flag(Flags::Carry));
-        self.add_u8s(first, val)
+        let carry = self.is_flag(Flags::Carry);
+        self.clear_flag(Flags::Carry);
+        self.add_u8s(first, second, carry)
     }
 
     pub(crate) fn sub(&mut self, first: u8, second: u8) -> u8 {
-        self.sub_u8s(first, second)
+        self.sub_u8s(first, second, false)
     }
 
     pub(crate) fn sbc(&mut self, first: u8, second: u8) -> u8 {
-        let val = second.wrapping_add(self.get_flag(Flags::Carry));
-        self.sub_u8s(first, val)
+        self.sub_u8s(first, second, self.is_flag(Flags::Carry))
     }
 
     pub(crate) fn inc(&mut self, reg: Reg8) {
diff --git a/src/processor/instructions/primitives.rs b/src/processor/instructions/primitives.rs
index 0520a1d..e50cfac 100644
--- a/src/processor/instructions/primitives.rs
+++ b/src/processor/instructions/primitives.rs
@@ -1,6 +1,6 @@
 use crate::{
     processor::{Cpu, Direction, Flags, SplitRegister},
-    util::{get_bit, get_rotation_carry, rotate},
+    util::{get_bit, get_rotation_carry, rotate, Nibbles},
 };
 use std::ops::{BitAnd, BitOr};
 
@@ -82,14 +82,6 @@ impl Cpu {
         rotated
     }
 
-    pub(crate) fn get_flag(&mut self, flag: Flags) -> u8 {
-        if get_bit(self.reg.af.get_low(), flag as u8) {
-            0x1
-        } else {
-            0x0
-        }
-    }
-
     pub(crate) fn is_flag(&self, flag: Flags) -> bool {
         get_bit(self.reg.af.get_low(), flag as u8)
     }
@@ -128,14 +120,14 @@ impl Cpu {
         result
     }
 
-    pub(crate) fn add_u8s(&mut self, first: u8, second: u8) -> u8 {
-        let (result, carry) = first.overflowing_add(second);
+    pub(crate) fn add_u8s(&mut self, first: u8, second: u8, with_carry: bool) -> u8 {
+        let (result, carry) = first.carrying_add(second, with_carry);
         self.clear_flag(Flags::NSubtract);
         self.set_or_clear_flag(Flags::Carry, carry);
         self.set_or_clear_flag(Flags::Zero, result == 0x0);
         self.set_or_clear_flag(
             Flags::HalfCarry,
-            (((first & 0xF).wrapping_add(second & 0xF)) & 0x10) == 0x10,
+            first.get_low_nibble() + second.get_low_nibble() + if with_carry { 1 } else { 0 } > 0xF,
         );
         result
     }
@@ -151,14 +143,15 @@ impl Cpu {
         result
     }
 
-    pub(crate) fn sub_u8s(&mut self, first: u8, second: u8) -> u8 {
-        let (result, carry) = first.overflowing_sub(second);
+    pub(crate) fn sub_u8s(&mut self, first: u8, second: u8, with_carry: bool) -> u8 {
+        let (result, carry) = first.borrowing_sub(second, with_carry);
         self.set_flag(Flags::NSubtract);
         self.set_or_clear_flag(Flags::Carry, carry);
         self.set_or_clear_flag(Flags::Zero, result == 0x0);
         self.set_or_clear_flag(
             Flags::HalfCarry,
-            (((first & 0xF).wrapping_sub(second & 0xF)) & 0x10) == 0x10,
+            first.get_low_nibble() - (second.get_low_nibble() + if with_carry { 1 } else { 0 })
+                > 0xF,
         );
         result
     }
diff --git a/src/processor/opcodes.rs b/src/processor/opcodes.rs
index b76a9b2..2bc00fc 100644
--- a/src/processor/opcodes.rs
+++ b/src/processor/opcodes.rs
@@ -951,7 +951,7 @@ impl Cpu {
             }
             0xC6 => {
                 let byte = self.ld_immediate_byte();
-                let val = self.add_u8s(self.reg.get_8(Reg8::A), byte);
+                let val = self.add_u8s(self.reg.get_8(Reg8::A), byte, false);
                 self.reg.set_8(Reg8::A, val);
                 2
             }
@@ -1047,7 +1047,7 @@ impl Cpu {
             }
             0xD6 => {
                 let byte = self.ld_immediate_byte();
-                let val = self.sub_u8s(self.reg.get_8(Reg8::A), byte);
+                let val = self.sub_u8s(self.reg.get_8(Reg8::A), byte, false);
                 self.reg.set_8(Reg8::A, val);
                 2
             }