Implement addressing on Word structs

This is more useful than taking 2 MixBits and more easily keeps the sign
of the Word in scope.

diff --git a/src/main.rs b/src/main.rs
index 727b3f6..9108572 100644 (file)
--- a/src/main.rs
+++ b/src/main.rs
@@ -40,16 +40,27 @@ impl Word {
     // right-hand part of the field.
     fn field_specification(&self, l: usize, r: usize) -> Word {
         let mut sign = false;
+        let mut l_clamp = l;
         if l == 0 {
             sign = self.sign;
+        } else {
+            l_clamp = l - 1;
         }
         let r_clamp = r % 5;
         let mut bytes = [MixBit::default(); 5];
-        for n in l..r_clamp {
+        for n in l_clamp..r_clamp {
             bytes[n] = self.bytes[n];
         }
         Word { sign, bytes }
     }
+
+    fn address(&self) -> i16 {
+        let magnitude = ((self.bytes[0].value() as i16) << 6) | self.bytes[1].value() as i16;
+        match self.sign {
+            true => magnitude,
+            false => -magnitude,
+        }
+    }
 }
 
 // There are nine registers in MIX.
@@ -108,8 +119,8 @@ impl Machine {
 fn main() {
     let fs = (Word {
         sign: true,
-        bytes: [MixBit { v: 255 }; 5],
+        bytes: [MixBit { v: 63 }; 5],
     })
-    .field_specification(0, 2);
-    println!("{:?}", address(fs.bytes[0], fs.bytes[1]));
+    .field_specification(1, 2);
+    println!("{:?}", fs.address());
 }