Add range type to helix stdx

helix-stdx/src/lib.rs

@@ -1,4 +1,7 @@
 pub mod env;
 pub mod faccess;
 pub mod path;
+pub mod range;
 pub mod rope;
+
+pub use range::Range;

helix-stdx/src/range.rs

@@ -0,0 +1,103 @@
+use std::ops::{self, RangeBounds};
+
+/// A range of `char`s within the text.
+#[derive(Debug, Clone, Copy, PartialOrd, Ord, PartialEq, Eq)]
+pub struct Range<T = usize> {
+    pub start: T,
+    pub end: T,
+}
+
+impl<T: PartialOrd> Range<T> {
+    pub fn contains(&self, other: Self) -> bool {
+        self.start <= other.start && other.end <= self.end
+    }
+    pub fn is_empty(&self) -> bool {
+        self.end <= self.start
+    }
+}
+
+impl<T> RangeBounds<T> for Range<T> {
+    fn start_bound(&self) -> ops::Bound<&T> {
+        ops::Bound::Included(&self.start)
+    }
+
+    fn end_bound(&self) -> ops::Bound<&T> {
+        ops::Bound::Excluded(&self.end)
+    }
+}
+
+/// Returns true if all ranges yielded by `sub_set` are contained by
+/// `super_set`. This is essentially an optimized implementation of
+/// `sub_set.all(|rb| super_set.any(|ra| ra.contains(rb)))` that runs in O(m+n)
+/// instead of O(mn) (and in many cases faster).
+///
+/// Both iterators must uphold a the following invariants:
+/// * ranges must not overlap (but they can be adjacent)
+/// * ranges must be sorted
+pub fn is_subset<const ALLOW_EMPTY: bool>(
+    mut super_set: impl Iterator<Item = Range>,
+    mut sub_set: impl Iterator<Item = Range>,
+) -> bool {
+    let (mut super_range, mut sub_range) = (super_set.next(), sub_set.next());
+    loop {
+        match (super_range, sub_range) {
+            // skip over irrelevant ranges
+            (Some(ra), Some(rb))
+                if ra.end <= rb.start && (ra.start != rb.start || !ALLOW_EMPTY) =>
+            {
+                super_range = super_set.next();
+            }
+            (Some(ra), Some(rb)) => {
+                if ra.contains(rb) {
+                    sub_range = sub_set.next();
+                } else {
+                    return false;
+                }
+            }
+            (None, Some(_)) => {
+                // exhausted `super_set`, we can't match the reminder of `sub_set`
+                return false;
+            }
+            (_, None) => {
+                // no elements from `sub_sut` left to match, `super_set` contains `sub_set`
+                return true;
+            }
+        }
+    }
+}
+
+pub fn is_exact_subset(
+    mut super_set: impl Iterator<Item = Range>,
+    mut sub_set: impl Iterator<Item = Range>,
+) -> bool {
+    let (mut super_range, mut sub_range) = (super_set.next(), sub_set.next());
+    let mut super_range_matched = true;
+    loop {
+        match (super_range, sub_range) {
+            // skip over irrelevant ranges
+            (Some(ra), Some(rb)) if ra.end <= rb.start && ra.start < rb.start => {
+                if !super_range_matched {
+                    return false;
+                }
+                super_range_matched = false;
+                super_range = super_set.next();
+            }
+            (Some(ra), Some(rb)) => {
+                if ra.contains(rb) {
+                    super_range_matched = true;
+                    sub_range = sub_set.next();
+                } else {
+                    return false;
+                }
+            }
+            (None, Some(_)) => {
+                // exhausted `super_set`, we can't match the reminder of `sub_set`
+                return false;
+            }
+            (_, None) => {
+                // no elements from `sub_sut` left to match, `super_set` contains `sub_set`
+                return super_set.next().is_none();
+            }
+        }
+    }
+}