1 files changed, 54 insertions, 0 deletions
diff --git a/src/math.rs b/src/math.rs
new file mode 100644
index 0000000..9de5889
--- /dev/null
+++ b/src/math.rs
@@ -0,0 +1,54 @@
+use std::ops::{Bound, Range, RangeBounds};
+
+/// Divide `n` by `divisor`, and round up to the nearest integer
+/// if not evenly divisable.
+#[inline]
+pub(super) fn div_round_up(n: usize, divisor: usize) -> usize {
+    debug_assert!(divisor != 0, "Division by zero!");
+    if n == 0 {
+        0
+    } else {
+        (n - 1) / divisor + 1
+    }
+}
+
+/// Normalize arbitrary `RangeBounds` to a `Range`
+pub(super) fn simplify_range(range: impl RangeBounds<usize>, len: usize) -> Range<usize> {
+    let start = match range.start_bound() {
+        Bound::Unbounded => 0,
+        Bound::Included(&i) if i <= len => i,
+        Bound::Excluded(&i) if i < len => i + 1,
+        bound => panic!("range start {:?} should be <= length {}", bound, len),
+    };
+    let end = match range.end_bound() {
+        Bound::Unbounded => len,
+        Bound::Excluded(&i) if i <= len => i,
+        Bound::Included(&i) if i < len => i + 1,
+        bound => panic!("range end {:?} should be <= length {}", bound, len),
+    };
+    if start > end {
+        panic!(
+            "range start {:?} should be <= range end {:?}",
+            range.start_bound(),
+            range.end_bound()
+        );
+    }
+    start..end
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn check_div_round_up() {
+        assert_eq!(0, div_round_up(0, 5));
+        assert_eq!(1, div_round_up(5, 5));
+        assert_eq!(1, div_round_up(1, 5));
+        assert_eq!(2, div_round_up(3, 2));
+        assert_eq!(
+            usize::max_value() / 2 + 1,
+            div_round_up(usize::max_value(), 2)
+        );
+    }
+}