WIP

gpui/src/util.rs

@@ -0,0 +1,77 @@
+use rand::prelude::*;
+use std::cmp::Ordering;
+
+pub fn pre_inc(value: &mut usize) -> usize {
+    *value += 1;
+    *value
+}
+
+pub fn post_inc(value: &mut usize) -> usize {
+    let prev = *value;
+    *value += 1;
+    prev
+}
+
+pub fn find_insertion_index<'a, F, T, E>(slice: &'a [T], mut f: F) -> Result<usize, E>
+where
+    F: FnMut(&'a T) -> Result<Ordering, E>,
+{
+    use Ordering::*;
+
+    let s = slice;
+    let mut size = s.len();
+    if size == 0 {
+        return Ok(0);
+    }
+    let mut base = 0usize;
+    while size > 1 {
+        let half = size / 2;
+        let mid = base + half;
+        // mid is always in [0, size), that means mid is >= 0 and < size.
+        // mid >= 0: by definition
+        // mid < size: mid = size / 2 + size / 4 + size / 8 ...
+        let cmp = f(unsafe { s.get_unchecked(mid) })?;
+        base = if cmp == Greater { base } else { mid };
+        size -= half;
+    }
+    // base is always in [0, size) because base <= mid.
+    let cmp = f(unsafe { s.get_unchecked(base) })?;
+    if cmp == Equal {
+        Ok(base)
+    } else {
+        Ok(base + (cmp == Less) as usize)
+    }
+}
+
+pub struct RandomCharIter<T: Rng>(T);
+
+impl<T: Rng> RandomCharIter<T> {
+    pub fn new(rng: T) -> Self {
+        Self(rng)
+    }
+}
+
+impl<T: Rng> Iterator for RandomCharIter<T> {
+    type Item = char;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.0.gen_bool(1.0 / 5.0) {
+            Some('\n')
+        } else {
+            Some(self.0.gen_range(b'a', b'z' + 1).into())
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_find_insertion_index() {
+        assert_eq!(
+            find_insertion_index(&[0, 4, 8], |probe| Ok::<Ordering, ()>(probe.cmp(&2))),
+            Ok(1)
+        );
+    }
+}