From 8b86db359e8bc754d9c02755e263201c1690f75a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20L=C3=B6ffler?= <me@fatalerrorcoded.eu>
Date: Sat, 28 Jan 2023 05:39:05 +0100
Subject: [PATCH] stack instructions

---
 src/emulator/instructions/transfer.rs | 73 ++++++++++++++++++++++++++-
 src/emulator/main.rs                  | 10 ++++
 src/emulator/structs.rs               |  2 +-
 3 files changed, 83 insertions(+), 2 deletions(-)

diff --git a/src/emulator/instructions/transfer.rs b/src/emulator/instructions/transfer.rs
index db7102e..4075ac6 100644
--- a/src/emulator/instructions/transfer.rs
+++ b/src/emulator/instructions/transfer.rs
@@ -1,4 +1,7 @@
-use crate::{get_register, get_register_pair, set_register, EmulatorState, Register};
+use crate::{
+    get_register, get_register_pair, set_register, structs::set_register_pair, EmulatorState,
+    Register,
+};
 
 /// Move (copy) value from source to destination register
 pub fn mov(src: Register, dest: Register, state: &mut EmulatorState) {
@@ -34,3 +37,71 @@ pub fn lhld(address: u16, state: &mut EmulatorState) {
     state.l = state.memory[address as usize];
     state.h = state.memory[address as usize + 1];
 }
+
+/* STACK */
+/// Push a 16-bit value from a register pair onto the stack
+pub fn push_reg(register: Register, state: &mut EmulatorState) {
+    push(get_register_pair(register, state), state);
+}
+
+pub fn push(value: u16, state: &mut EmulatorState) {
+    (state.sp, ..) = state.sp.overflowing_sub(2);
+    state.write_word(state.sp, value);
+}
+
+/// Pop a 16-bit value from the stack into a register pair
+pub fn pop_reg(register: Register, state: &mut EmulatorState) {
+    set_register_pair(register, pop(state), state);
+}
+
+pub fn pop(state: &mut EmulatorState) -> u16 {
+    let value = state.read_word(state.sp);
+    (state.sp, ..) = state.sp.overflowing_add(2);
+    value
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::EmulatorState;
+
+    #[test]
+    fn push() {
+        // From the altairclone.com 8080 programmers manual:
+        // (1) The most significant 8 bits of data are stored at the
+        //     memory address one less than the contents of the
+        //     stack pointer.
+        // (2) The least significant 8 bits of data are stored at the
+        //     memory address two less than the contents of the
+        //     stack pointer.
+        // (3) The stack pointer is automatically decremented by two.
+        let mut state = EmulatorState {
+            sp: 0x12,
+            ..Default::default()
+        };
+
+        super::push(0x1234, &mut state);
+        assert_eq!(state.sp, 0x10);
+        assert_eq!(state.memory[0x10..=0x11], [0x34, 0x12]);
+    }
+
+    #[test]
+    fn pop() {
+        // From the altairclone.com 8080 programmers manual:
+        // (1) The second register of the pair, or the least significant
+        //     8 bits of the program counter, are loaded from the
+        //     memory address held in the stack pointer.
+        // (2) The first register of the pair, or the most significant
+        //     8 bits of the program counter, are loaded from the
+        //     memory address one greater than the address held in
+        //     the stack pointer.
+        // (3) The stack pointer is automatically incremented by two.
+        let mut state = EmulatorState {
+            sp: 0x10,
+            ..Default::default()
+        };
+
+        state.memory[0x10] = 0x34;
+        state.memory[0x11] = 0x12;
+        assert_eq!(super::pop(&mut state), 0x1234);
+    }
+}
diff --git a/src/emulator/main.rs b/src/emulator/main.rs
index 378a6b5..d2aa2b9 100644
--- a/src/emulator/main.rs
+++ b/src/emulator/main.rs
@@ -80,6 +80,16 @@ fn tick(state: &mut EmulatorState) {
         0x22 => transfer::shld(state.next_word(), state),                 // SHLD
         0x2a => transfer::lhld(state.next_word(), state),                 // LHLD
 
+        // Stack instructions
+        0xc1 => transfer::pop_reg(Register::B, state), // POP B
+        0xc5 => transfer::push_reg(Register::B, state), // PUSH B
+        0xd1 => transfer::pop_reg(Register::D, state), // POP D
+        0xd5 => transfer::push_reg(Register::D, state), // PUSH D
+        0xe1 => transfer::pop_reg(Register::H, state), // POP H
+        0xe5 => transfer::push_reg(Register::H, state), // PUSH H
+        0xf1 => transfer::pop_reg(Register::A, state), // POP PSW
+        0xf5 => transfer::push_reg(Register::A, state), // PUSH PSW
+
         /* Maths */
         // INR
         0x04 => arithmetic::inr(Register::B, state),
diff --git a/src/emulator/structs.rs b/src/emulator/structs.rs
index 4d586d7..a129516 100644
--- a/src/emulator/structs.rs
+++ b/src/emulator/structs.rs
@@ -241,7 +241,7 @@ mod tests {
     fn write_word() {
         let mut state = EmulatorState::default();
         state.write_word(0x10, 0x1234);
-        assert_eq!([0x34, 0x12], state.memory[0x10..0x12]);
+        assert_eq!(state.memory[0x10..=0x11], [0x34, 0x12]);
     }
 
     #[test]