1 files changed, 204 insertions, 0 deletions
diff --git a/src/regex/byte_range.rs b/src/regex/byte_range.rs
new file mode 100644
index 0000000..b7642c1
--- /dev/null
+++ b/src/regex/byte_range.rs
@@ -0,0 +1,204 @@
+use std::ops::RangeInclusive;
+
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub struct ByteRange {
+    /// inclusive
+    from: u8,
+    /// inclusive
+    to: u8,
+}
+
+impl From<RangeInclusive<u8>> for ByteRange {
+    fn from(value: RangeInclusive<u8>) -> Self {
+        Self::new_range(*value.start(), *value.end())
+    }
+}
+
+impl ByteRange {
+    pub fn new_range(from: u8, to: u8) -> Self {
+        assert!(from <= to, "{from} <= {to}");
+        Self { from, to }
+    }
+
+    pub fn new_single(c: u8) -> Self {
+        Self::new_range(c, c)
+    }
+
+    pub fn contains(&self, c: u8) -> bool {
+        self.from <= c && c <= self.to
+    }
+
+    pub fn overlaps(&self, other: Self) -> bool {
+        self.from.max(other.from) <= self.to.min(other.to)
+    }
+
+    pub fn split_to_disjoint(ranges: Vec<ByteRange>) -> Vec<ByteRange> {
+        if ranges.is_empty() {
+            return vec![];
+        }
+    
+        let mut points: Vec<u8> = Vec::new();
+        for r in &ranges {
+            points.push(r.from);
+            if r.to != u8::MAX {
+                points.push(r.to + 1);
+            }
+        }
+    
+        points.sort_unstable();
+        points.dedup();
+    
+        let mut out = Vec::new();
+    
+        for window in points.windows(2) {
+            let start = window[0];
+            let end_exclusive = window[1];
+    
+            if start >= end_exclusive {
+                continue;
+            }
+    
+            let mut active = false;
+    
+            for r in &ranges {
+                if r.from <= start && start <= r.to {
+                    active = true;
+                    break;
+                }
+            }
+    
+            if active {
+                out.push(ByteRange {
+                    from: start,
+                    to: end_exclusive - 1,
+                });
+            }
+        }
+    
+        out
+    }
+}
+
+#[test]
+fn byterange_test() {
+    assert_eq!(
+        ByteRange::split_to_disjoint(vec![
+            ByteRange::new_range(b'a', b'z'),
+            ByteRange::new_single(b'm')
+        ]),
+        vec![
+            ByteRange::new_range(b'a', b'l'),
+            ByteRange::new_single(b'm'),
+            ByteRange::new_range(b'n', b'z'),
+        ]
+    );
+}
+
+impl std::fmt::Debug for ByteRange {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        if self.from == self.to {
+            write!(f, "{}", [self.from].escape_ascii())
+        } else {
+            write!(
+                f,
+                "{}-{}",
+                [self.from].escape_ascii(),
+                [self.to].escape_ascii()
+            )
+        }
+    }
+}
+
+#[cfg(test)]
+mod non_overlapping_tests {
+    use std::ops::RangeInclusive;
+
+    use super::ByteRange;
+
+    fn middle(r: ByteRange) -> u8 {
+        let a = r.from as u8;
+        let b = r.to as u8;
+        (a + (b - a) / 2) as u8
+    }
+
+    fn prev(c: u8) -> u8 {
+        c - 1
+    }
+
+    fn next(c: u8) -> u8 {
+        c + 1
+    }
+
+    fn run(ranges: Vec<RangeInclusive<u8>>) {
+        let ranges1: Vec<ByteRange> = ranges.into_iter().map(Into::into).collect();
+        let ranges2 = ByteRange::split_to_disjoint(ranges1.clone());
+
+        let r1 = |c| ranges1.iter().any(|cr| cr.contains(c));
+        let r2 = |c| ranges2.iter().any(|cr| cr.contains(c));
+
+        for &range in ranges1.iter() {
+            assert!(r1(range.from));
+            assert!(r1(range.to));
+            assert!(r1(middle(range)));
+
+            assert!(r2(range.from));
+            assert!(r2(range.to));
+            assert!(r2(middle(range)));
+
+            assert_eq!(r1(prev(range.from)), r2(prev(range.from)));
+            assert_eq!(r1(next(range.from)), r2(next(range.from)));
+        }
+
+        for i in 0..ranges2.len() {
+            for j in 0..i {
+                assert!(
+                    !ranges2[i].overlaps(ranges2[j]),
+                    "{i} and {j} overlap: {:?}, {:?}",
+                    ranges2[i],
+                    ranges2[j]
+                );
+            }
+        }
+    }
+
+    #[test]
+    fn overlap_correct() {
+        assert!(ByteRange::new_range(b'a', b'g').overlaps(ByteRange::new_single(b'f')));
+        assert!(!ByteRange::new_range(b'a', b'g').overlaps(ByteRange::new_single(b'h')));
+    }
+
+    #[test]
+    fn empty() {
+        run(vec![]);
+    }
+
+    #[test]
+    fn singleton() {
+        run(vec![b'0'..=b'9']);
+    }
+
+    #[test]
+    fn contained1() {
+        run(vec![b'0'..=b'9', b'5'..=b'6']);
+    }
+
+    #[test]
+    fn contained2() {
+        run(vec![b'5'..=b'6', b'0'..=b'9']);
+    }
+
+    #[test]
+    fn overlap2() {
+        run(vec![b'1'..=b'6', b'4'..=b'9'])
+    }
+
+    #[test]
+    fn overlap3() {
+        run(vec![b'a'..=b'f', b'd'..=b'j', b'g'..=b'm'])
+    }
+
+    #[test]
+    fn overlap4() {
+        run(vec![b'a'..=b'f', b'd'..=b'j', b'g'..=b'm', b'k'..=b'q'])
+    }
+}