Partially restructure the library

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

1 files changed, 51 insertions, 0 deletions

diff --git a/src/components/program_memory.rs b/src/components/program_memory.rs
new file mode 100644
index 0000000..bcfbcae
--- /dev/null
+++ b/src/components/program_memory.rs
@@ -0,0 +1,51 @@
+pub struct ProgramMemory {
+    pub mem: [u8; 65536],
+    pub pc: u16,
+}
+
+impl ProgramMemory {
+    pub fn new() -> Self {
+        Self {
+            mem: [0; 65536],
+            pc: 0,
+        }
+    }
+
+    pub fn load_program(&mut self, bytecode: &[u8]) {
+        let length = std::cmp::min(bytecode.len(), 65536);
+        self.mem[..length].copy_from_slice(&bytecode[..length]);
+        self.mem[length..65536].fill(0);
+    }
+
+    pub fn read_u8(&self, addr: u16) -> u8 {
+        self.mem[addr as usize]
+    }
+
+    pub fn write_u8(&mut self, val: u8, addr: u16) {
+        self.mem[addr as usize] = val;
+    }
+
+    pub fn read_u8_next(&mut self) -> u8 {
+        let byte = self.mem[self.pc as usize];
+        self.pc = self.pc.wrapping_add(1);
+        byte
+    }
+
+    pub fn read_u16(&self, addr: u16) -> u16 {
+        let byte_high = self.read_u8(addr);
+        let byte_low = self.read_u8(addr.wrapping_add(1));
+        u16::from_be_bytes([byte_high, byte_low])
+    }
+
+    pub fn write_u16(&mut self, val: u16, addr: u16) {
+        let [byte_high, byte_low] = val.to_be_bytes();
+        self.write_u8(byte_high, addr);
+        self.write_u8(byte_low, addr.wrapping_add(1));
+    }
+
+    pub fn read_u16_next(&mut self) -> u16 {
+        let byte_high = self.read_u8_next();
+        let byte_low = self.read_u8_next();
+        u16::from_be_bytes([byte_high, byte_low])
+    }
+}