From d85c7b8a9803fd447ceba48e28d4f420bd079d0e Mon Sep 17 00:00:00 2001
From: Nick Krichevsky <nick@ollien.com>
Date: Sat, 9 Apr 2022 13:57:50 -0400
Subject: [PATCH] Add support for programatically manipulating 16 bit registers

---
 src/register.rs | 70 ++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 69 insertions(+), 1 deletion(-)

diff --git a/src/register.rs b/src/register.rs
index 62dcda1..dda5d33 100644
--- a/src/register.rs
+++ b/src/register.rs
@@ -23,6 +23,12 @@ pub enum SingleEightBit {
     L,
 }
 
+#[derive(Debug, Clone, Copy, strum_macros::Display)]
+pub enum SixteenBit {
+    Combined(Combined),
+    Single(SingleSixteenBit),
+}
+
 // Combined represents a pair of two registers taht can be acted on as a single 8 bit
 // 16 bit register.
 #[derive(Debug, Clone, Copy, strum_macros::Display)]
@@ -33,6 +39,12 @@ pub enum Combined {
     HL,
 }
 
+#[derive(Debug, Clone, Copy, strum_macros::Display)]
+pub enum SingleSixteenBit {
+    StackPointer,
+    ProgramCounter,
+}
+
 /// Registers holds all of the registers for the Gameboy
 #[derive(Debug, Clone)]
 pub struct Registers {
@@ -141,7 +153,24 @@ impl Registers {
         *register_ref = value;
     }
 
-    /// Get the value of a pair of registers
+    /// Get the value of a 16 bit register, whether it's natively a 16 bit register or a combination of
+    /// 8 bit registers
+    pub fn get_16bit_register(&self, register: SixteenBit) -> u16 {
+        match register {
+            SixteenBit::Single(single) => self.get_single_16bit_register(single),
+            SixteenBit::Combined(combined) => self.get_combined_register(combined),
+        }
+    }
+
+    /// Get the value of a single 16 bit register (i.e. a natively 16 bit register)
+    pub fn get_single_16bit_register(&self, register: SingleSixteenBit) -> u16 {
+        match register {
+            SingleSixteenBit::StackPointer => self.stack_pointer,
+            SingleSixteenBit::ProgramCounter => self.program_counter,
+        }
+    }
+
+    /// Get the value of combined single 16 bit register (i.e. a combination of two 8 bit registers)
     pub fn get_combined_register(&self, registers: Combined) -> u16 {
         let (left_register, right_register) = self.get_register_values_for_combined(registers);
         let mut res = 0_u16;
@@ -151,6 +180,25 @@ impl Registers {
         res
     }
 
+    /// Set the value of a 16 bit register, whether it's natively a 16 bit register or a combination of
+    /// 8 bit registers
+    pub fn set_16bit_register(&mut self, register: SixteenBit, value: u16) {
+        match register {
+            SixteenBit::Single(single) => self.set_single_16bit_register(single, value),
+            SixteenBit::Combined(combined) => self.set_combined_register(combined, value),
+        }
+    }
+
+    /// Set the value of a single 16 bit register (i.e. a natively 16 bit register)
+    pub fn set_single_16bit_register(&mut self, register: SingleSixteenBit, value: u16) {
+        let register_ref = match register {
+            SingleSixteenBit::StackPointer => &mut self.stack_pointer,
+            SingleSixteenBit::ProgramCounter => &mut self.program_counter,
+        };
+
+        *register_ref = value;
+    }
+
     /// Set the value of a pair of registers
     pub fn set_combined_register(&mut self, registers: Combined, value: u16) {
         let (left_register, right_register) = self.get_register_mut_refs_for_combined(registers);
@@ -268,4 +316,24 @@ mod tests {
             "got {combined_value:0b}, expected 0011001111001100"
         );
     }
+
+    #[test_case(Combined::AF)]
+    #[test_case(Combined::BC)]
+    #[test_case(Combined::DE)]
+    #[test_case(Combined::HL)]
+    fn test_set_sixteen_bit_register_combined(register: Combined) {
+        let mut registers = Registers::new();
+        registers.set_16bit_register(SixteenBit::Combined(register), 0x1122);
+
+        assert_eq!(0x1122, registers.get_combined_register(register));
+    }
+
+    #[test_case(SingleSixteenBit::StackPointer)]
+    #[test_case(SingleSixteenBit::ProgramCounter)]
+    fn test_set_sixteen_bit_register_single(register: SingleSixteenBit) {
+        let mut registers = Registers::new();
+        registers.set_16bit_register(SixteenBit::Single(register), 0x1122);
+
+        assert_eq!(0x1122, registers.get_single_16bit_register(register));
+    }
 }