Add note.

machine/src/core.rs

@@ -13,7 +13,7 @@ pub fn index_of_byte(addr: u32) -> usize {
     (addr & 3) as usize
 }
 
-/// Get the address to the map of the memory cells which is not empty (a multiple of 4).
+/// Get the address of the memory cells which is not empty (a multiple of 4).
 pub fn index_to_word(addr: u32) -> u32 {
     (addr & !3) as u32
 }
@@ -28,6 +28,7 @@ impl Word<u8> {
 }
 
 impl Word<u8> {
+    //TODO if the byte isn't the lowest byte then this doesn't make sense?
     pub fn sign_extend_byte(byte: u8, loc: usize) -> Self {
         let sign = byte as i8 >> 7;
         let mut result: [u8; MEMORY_CELL_BYTES] = [sign as u8; MEMORY_CELL_BYTES];