diff options
| -rw-r--r-- | src/libcore/iter/range.rs | 26 |
1 files changed, 12 insertions, 14 deletions
diff --git a/src/libcore/iter/range.rs b/src/libcore/iter/range.rs index 9e54e69bc55..7a08d6d1ff3 100644 --- a/src/libcore/iter/range.rs +++ b/src/libcore/iter/range.rs @@ -202,26 +202,24 @@ macro_rules! step_identical_methods { #[inline] fn forward(start: Self, n: usize) -> Self { - match Self::forward_checked(start, n) { - Some(result) => result, - None => { - let result = Add::add(start, n as Self); - // add one modular cycle to ensure overflow occurs - Add::add(Add::add(result as $u, $u::MAX), 1) as Self - } + // In debug builds, trigger a panic on overflow. + // This should optimize completely out in release builds. + if Self::forward_checked(start, n).is_none() { + let _ = Add::add(Self::MAX, 1); } + // Do wrapping math to allow e.g. `Step::forward(-128u8, 255)`. + start.wrapping_add(n as Self) as Self } #[inline] fn backward(start: Self, n: usize) -> Self { - match Self::backward_checked(start, n) { - Some(result) => result, - None => { - let result = Sub::sub(start, n as Self); - // sub one modular cycle to ensure overflow occurs - Sub::sub(Sub::sub(result as $u, $u::MAX), 1) as Self - } + // In debug builds, trigger a panic on overflow. + // This should optimize completely out in release builds. + if Self::backward_checked(start, n).is_none() { + let _ = Sub::sub(Self::MIN, 1); } + // Do wrapping math to allow e.g. `Step::backward(127u8, 255)`. + start.wrapping_sub(n as Self) as Self } }; } |