Simplify {clz,clo,se}XX parsing and exec, add simple unit test example scripts

crsn/src/builtin/defs.rs

@@ -41,7 +41,7 @@ pub enum LdsValue {
     Chars(String),
 }
 
-#[derive(Clone, Copy, Debug, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub struct BitSlice {
     pub width: u32,
     pub src_pos: u32,
@@ -80,7 +80,50 @@ impl BitSlice {
         Self::default()
     }
 
+    /// Parse LEN (no SRC and DST)
+    pub fn parse1(src: &str, pos: &SourcePosition) -> Result<Option<Self>, CrsnError> {
+        match Self::parse(src, pos) {
+            Ok(Some(slice)) => {
+                if slice.src_pos != 0 || slice.dst_pos != 0 {
+                    return Err(CrsnError::Parse("Excess bit slice modifiers".into(), pos.clone()));
+                }
+
+                Ok(Some(BitSlice {
+                    width: slice.width,
+                    src_pos: 0,
+                    dst_pos: 0
+                }))
+            }
+            other => other
+        }
+    }
+
+    /// Parse LEN/SRC
+    pub fn parse2(src: &str, pos: &SourcePosition) -> Result<Option<Self>, CrsnError> {
+        match Self::parse(src, pos) {
+            Ok(Some(slice)) => {
+                if slice.src_pos != 0 {
+                    return Err(CrsnError::Parse("Excess bit slice modifiers".into(), pos.clone()));
+                }
+
+                Ok(Some(BitSlice {
+                    width: slice.width,
+                    src_pos: slice.dst_pos,
+                    dst_pos: 0
+                }))
+            }
+            other => other
+        }
+    }
+
+    /// Parse a bit slice LEN/DST/SRC
+    /// - String not starting with a digit is rejected as `Ok(None)`
+    /// - Empty string is parsed as a full slice
     pub fn parse(src: &str, pos: &SourcePosition) -> Result<Option<Self>, CrsnError> {
+        if src.is_empty() {
+            return Ok(Some(BitSlice::full()));
+        }
+
         if !src.starts_with(|c: char| c.is_ascii_digit()) {
             return Ok(None);
         }
@@ -97,6 +140,10 @@ impl BitSlice {
             dst_pos: numbers.get(1).copied().unwrap_or(0)
         };
 
+        if slice.width == 0 || slice.width > 64 {
+            return Err(CrsnError::Parse("Bit slice width must be 1-64".into(), pos.clone()));
+        }
+
         // Validation
         if slice.src_pos + slice.width > 64 {
             return Err(CrsnError::Parse("Invalid source bit slice".into(), pos.clone()));