Merge remote-tracking branch 'refs/remotes/origin/main'

dsa/common/src/isa/register.rs

@@ -23,38 +23,46 @@ pub enum Register {
     Rgf = 15,
 
     // special purpose
-    Zero = 16,
-    Acc = 17,
-    Spr = 18,
-    Bpr = 19,
-    Ret = 20,
-    Idr = 21,
-    Mmr = 22,
+    Acc = 16,
+    Spr = 17,
+    Bpr = 18,
+    Ret = 19,
+    Idr = 20,
+    Mmr = 21,
 
     // system - read only
-    Mar = 23,
-    Mdr = 24,
-    Sts = 25,
-    Cir = 26,
-    Pcx = 27,
+    Zero = 22,
+    Sts = 23,
+    Cir = 24,
+    Pcx = 25,
 
     #[default]
-    Null = 28,
+    Null = 26,
 }
 
 impl Register {
+    /// Total number of registers, not counting Null as it's not a real register.
+    /// reading or writing to Null is undefined behaviour.
+    pub const COUNT: u8 = Self::Null as u8;
+
+    /// # Safety
+    /// the caller must ensure that the index is always within the range 0..COUNT, failing to do so will result in undefined behaviour.
     #[must_use]
     #[inline]
     pub unsafe fn from_u8_unchecked(idx: u8) -> Self {
-        debug_assert!(idx <= Self::Null as u8);
+        debug_assert!(
+            idx < Self::COUNT,
+            "Tried to access a null register using the unchecked method. undefined behaviour alert!"
+        );
         unsafe { std::mem::transmute(idx) }
     }
 
     #[inline]
     pub fn from_u8(idx: u8) -> Result<Self, ()> {
-        if idx > 28 {
+        if idx >= Self::COUNT {
             return Err(());
         }
+
         Ok(unsafe { Self::from_u8_unchecked(idx) })
     }
 }
@@ -84,7 +92,6 @@ impl fmt::Display for Register {
                 Self::Rgf => "Rgf",
 
                 // special purpose
-                Self::Zero => "Zero",
                 Self::Acc => "Acc",
                 Self::Spr => "Spr",
                 Self::Bpr => "Bpr",
@@ -93,8 +100,7 @@ impl fmt::Display for Register {
                 Self::Mmr => "Mmr",
 
                 // system - read only
-                Self::Mar => "Mar",
-                Self::Mdr => "Mdr",
+                Self::Zero => "Zero",
                 Self::Sts => "Sts",
                 Self::Cir => "Cir",
                 Self::Pcx => "Pcx",
@@ -129,7 +135,6 @@ impl std::str::FromStr for Register {
             "rgf" => Ok(Self::Rgf),
 
             // special purpose
-            "zero" => Ok(Self::Zero),
             "acc" => Ok(Self::Acc),
             "spr" => Ok(Self::Spr),
             "bpr" => Ok(Self::Bpr),
@@ -138,8 +143,7 @@ impl std::str::FromStr for Register {
             "mmr" => Ok(Self::Mmr),
 
             // system - read only
-            "mar" => Ok(Self::Mar),
-            "mdr" => Ok(Self::Mdr),
+            "zero" => Ok(Self::Zero),
             "sts" => Ok(Self::Sts),
             "cir" => Ok(Self::Cir),
             "pcx" => Ok(Self::Pcx),