From 5e1730fd17145fd9db5c042b127e2f400c83738a Mon Sep 17 00:00:00 2001 From: ltdk Date: Wed, 17 Aug 2022 02:01:32 -0400 Subject: [PATCH] Make slice::reverse const --- library/core/src/slice/mod.rs | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs index e79d47c9f98..361862cdd52 100644 --- a/library/core/src/slice/mod.rs +++ b/library/core/src/slice/mod.rs @@ -674,8 +674,9 @@ pub const fn swap(&mut self, a: usize, b: usize) { /// assert!(v == [3, 2, 1]); /// ``` #[stable(feature = "rust1", since = "1.0.0")] + #[rustc_const_unstable(feature = "const_reverse", issue = "none")] #[inline] - pub fn reverse(&mut self) { + pub const fn reverse(&mut self) { let half_len = self.len() / 2; let Range { start, end } = self.as_mut_ptr_range(); @@ -698,9 +699,9 @@ pub fn reverse(&mut self) { revswap(front_half, back_half, half_len); #[inline] - fn revswap(a: &mut [T], b: &mut [T], n: usize) { - debug_assert_eq!(a.len(), n); - debug_assert_eq!(b.len(), n); + const fn revswap(a: &mut [T], b: &mut [T], n: usize) { + debug_assert!(a.len() == n); + debug_assert!(b.len() == n); // Because this function is first compiled in isolation, // this check tells LLVM that the indexing below is @@ -708,8 +709,10 @@ fn revswap(a: &mut [T], b: &mut [T], n: usize) { // lengths of the slices are known -- it's removed. let (a, b) = (&mut a[..n], &mut b[..n]); - for i in 0..n { + let mut i = 0; + while i < n { mem::swap(&mut a[i], &mut b[n - 1 - i]); + i += 1; } } } -- 2.44.0