Partially restructure the library

This also changes bit-shifting semantics, shifting left and then right
instead of the other way around.

1 files changed, 39 insertions, 0 deletions

diff --git a/src/components/stack.rs b/src/components/stack.rs
new file mode 100644
index 0000000..bbd7b68
--- /dev/null
+++ b/src/components/stack.rs
@@ -0,0 +1,39 @@
+pub struct Stack {
+    pub mem: [u8; 256],
+    pub sp: u8,
+}
+
+impl Stack {
+    pub fn new() -> Self {
+        Self {
+            mem: [0; 256],
+            sp: 0,
+        }
+    }
+
+    pub fn push_u8(&mut self, val: u8) {
+        self.mem[self.sp as usize] = val;
+        self.sp = self.sp.wrapping_add(1);
+    }
+
+    pub fn pop_u8(&mut self) -> u8 {
+        self.sp = self.sp.wrapping_sub(1);
+        self.mem[self.sp as usize]
+    }
+
+    pub fn push_u16(&mut self, val: u16) {
+        let [high, low] = u16::to_be_bytes(val);
+        self.mem[self.sp as usize] = high;
+        self.sp  = self.sp.wrapping_add(1);
+        self.mem[self.sp as usize] = low;
+        self.sp  = self.sp.wrapping_add(1);
+    }
+
+    pub fn pop_u16(&mut self) -> u16 {
+        self.sp  = self.sp.wrapping_sub(1);
+        let low  = self.mem[self.sp as usize];
+        self.sp  = self.sp.wrapping_sub(1);
+        let high = self.mem[self.sp as usize];
+        u16::from_be_bytes([high, low])
+    }
+}