Fix some IncBy constructor overflow edge cases reported on Reddit

Author: slightlyoutofphase

Cargo.toml

@@ -5,7 +5,7 @@ repository = "https://github.com/slightlyoutofphase/staticstep"
 documentation = "https://docs.rs/staticstep/"
 license = "MIT OR Apache-2.0"
 readme = "README.md"
-version = "0.2.2"
+version = "0.3.0"
 keywords = ["iterator", "iterators", "step", "range", "ranges"]
 categories = ["data-structures", "algorithms"]
 edition = "2018"

src/lib.rs

@@ -31,7 +31,7 @@ impl<T: Copy + Default + Step, const STEP: usize> IncBy<T, STEP> {
     };
     let end = match bounds.end_bound() {
       Included(&idx) => Step::forward(idx, STEP),
-      Excluded(&idx) => Step::forward(idx, STEP - 1),
+      Excluded(&idx) => Step::forward_checked(idx, STEP - 1).unwrap_or(idx),
       Unbounded => Default::default(),
     };
     IncBy { start, end }
@@ -60,10 +60,14 @@ impl<T: Copy + Default + Step, const STEP: usize> Iterator for IncBy<T, STEP> {
 
   #[inline(always)]
   fn next(&mut self) -> Option<T> {
-    if self.start <= Step::backward(self.end, STEP) {
-      let res = Some(self.start);
-      self.start = Step::forward(self.start, STEP);
-      res
+    if let Some(end_back) = Step::backward_checked(self.end, STEP) {
+      if self.start <= end_back {
+        let res = Some(self.start);
+        self.start = Step::forward(self.start, STEP);
+        res
+      } else {
+        None
+      }
     } else {
       None
     }

tests/test_staticstep.rs

@@ -236,3 +236,13 @@ fn dec_by_inclusive_char_range() {
   assert_eq!(r.next(), Some('A'));
   assert_eq!(r.next(), None);
 }
+
+#[test]
+fn inc_by_type_dependent_overflow() {
+  let mut r = (248u8..255u8).inc_by::<50>();
+  assert_eq!(r.next(), None);
+  let mut r2 = (248u32..255u32).inc_by::<{ usize::MAX }>();
+  assert_eq!(r2.next(), None);
+  let mut r3 = (248i32..255i32).inc_by::<{ u32::MAX as usize }>();
+  assert_eq!(r3.next(), None);
+}