Implement useful steps_between for all integers

We can use `usize::try_from` to convert steps from any size of integer.
This enables a meaningful `size_hint()` for larger ranges, rather than
always just `(0, None)`. Now they return the true `(len, Some(len))`
when it fits, otherwise `(usize::MAX, None)` for overflow.

1 files changed, 49 insertions, 0 deletions

diff --git a/src/libcore/tests/iter.rs b/src/libcore/tests/iter.rs
index a3f0b02e2fe..bcf0b7ec463 100644
--- a/src/libcore/tests/iter.rs
+++ b/src/libcore/tests/iter.rs
@@ -1,4 +1,5 @@
 use core::cell::Cell;
+use core::convert::TryFrom;
 use core::iter::*;
 use core::{i8, i16, isize};
 use core::usize;
@@ -1801,6 +1802,54 @@ fn test_range_inclusive_folds() {
 }
 
 #[test]
+fn test_range_size_hint() {
+    use core::usize::MAX as UMAX;
+    assert_eq!((0..100usize).size_hint(), (100, Some(100)));
+    assert_eq!((0..UMAX).size_hint(), (UMAX, Some(UMAX)));
+
+    let umax = u128::try_from(UMAX).unwrap();
+    assert_eq!((0..100u128).size_hint(), (100, Some(100)));
+    assert_eq!((0..umax).size_hint(), (UMAX, Some(UMAX)));
+    assert_eq!((0..umax + 1).size_hint(), (UMAX, None));
+
+    use core::isize::{MAX as IMAX, MIN as IMIN};
+    assert_eq!((-100..100isize).size_hint(), (200, Some(200)));
+    assert_eq!((IMIN..IMAX).size_hint(), (UMAX, Some(UMAX)));
+
+    let imin = i128::try_from(IMIN).unwrap();
+    let imax = i128::try_from(IMAX).unwrap();
+    assert_eq!((-100..100i128).size_hint(), (200, Some(200)));
+    assert_eq!((imin..imax).size_hint(), (UMAX, Some(UMAX)));
+    assert_eq!((imin..imax + 1).size_hint(), (UMAX, None));
+}
+
+#[test]
+fn test_range_inclusive_size_hint() {
+    use core::usize::MAX as UMAX;
+    assert_eq!((0..=100usize).size_hint(), (101, Some(101)));
+    assert_eq!((0..=UMAX - 1).size_hint(), (UMAX, Some(UMAX)));
+    assert_eq!((0..=UMAX).size_hint(), (UMAX, None));
+
+    let umax = u128::try_from(UMAX).unwrap();
+    assert_eq!((0..=100u128).size_hint(), (101, Some(101)));
+    assert_eq!((0..=umax - 1).size_hint(), (UMAX, Some(UMAX)));
+    assert_eq!((0..=umax).size_hint(), (UMAX, None));
+    assert_eq!((0..=umax + 1).size_hint(), (UMAX, None));
+
+    use core::isize::{MAX as IMAX, MIN as IMIN};
+    assert_eq!((-100..=100isize).size_hint(), (201, Some(201)));
+    assert_eq!((IMIN..=IMAX - 1).size_hint(), (UMAX, Some(UMAX)));
+    assert_eq!((IMIN..=IMAX).size_hint(), (UMAX, None));
+
+    let imin = i128::try_from(IMIN).unwrap();
+    let imax = i128::try_from(IMAX).unwrap();
+    assert_eq!((-100..=100i128).size_hint(), (201, Some(201)));
+    assert_eq!((imin..=imax - 1).size_hint(), (UMAX, Some(UMAX)));
+    assert_eq!((imin..=imax).size_hint(), (UMAX, None));
+    assert_eq!((imin..=imax + 1).size_hint(), (UMAX, None));
+}
+
+#[test]
 fn test_repeat() {
     let mut it = repeat(42);
     assert_eq!(it.next(), Some(42));