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rust source #1
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mrustc (master)
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Source code
#![feature(specialization)] #![feature(trusted_len)] #![feature(core_intrinsics)] pub fn foo3(x: &[u32], y: &[u32]) -> u32 { let mut sum = 0; let chunk_size = y.len(); for c in 0..chunk_size { let y = y[c]; for chunk in x.chunks_exact(chunk_size) { sum += chunk[c] + y; } } sum } pub fn foo2(x: &[u32], y: &[u32]) -> u32 { let mut sum = 0; let chunk_size = y.len(); for (c, y) in Enumerate::new(y.iter()) { for chunk in x.chunks_exact(chunk_size) { sum += chunk[c] + y; } } sum } pub fn foo1(x: &[u32], y: &[u32]) -> u32 { let mut sum = 0; let chunk_size = y.len(); for (c, y) in Iter::new(y).enumerate() { for chunk in x.chunks_exact(chunk_size) { sum += chunk[c] + y; } } sum } pub fn foo0(x: &[u32], y: &[u32]) -> u32 { let mut sum = 0; let chunk_size = y.len(); for (c, y) in y.iter().enumerate() { for chunk in x.chunks_exact(chunk_size) { sum += chunk[c] + y; } } sum } struct Iter<'a> { ptr: *const u32, len: usize, phantom: std::marker::PhantomData<&'a [u32]>, } impl<'a> Iter<'a> { fn new(v: &'a [u32]) -> Iter<'a> { Iter { ptr: v.as_ptr(), len: v.len(), phantom: std::marker::PhantomData, } } } impl<'a> Iterator for Iter<'a> { type Item = &'a u32; #[inline] fn next(&mut self) -> Option<&'a u32> { unsafe { if self.len == 0 { return None; } let item = &*self.ptr; self.ptr = self.ptr.add(1); self.len -= 1; Some(item) } } } struct Enumerate<I> { iter: I, count: usize, len: usize, } impl<I: Iterator> Enumerate<I> { fn new(iter: I) -> Self { EnumerateImpl::new(iter) } } impl<I> Iterator for Enumerate<I> where I: Iterator, { type Item = (usize, <I as Iterator>::Item); #[inline] fn next(&mut self) -> Option<(usize, <I as Iterator>::Item)> { EnumerateImpl::next(self) } } // Enumerate specialization trait #[doc(hidden)] trait EnumerateImpl<I> { type Item; fn new(iter: I) -> Self; fn next(&mut self) -> Option<(usize, Self::Item)>; } impl<I> EnumerateImpl<I> for Enumerate<I> where I: Iterator, { type Item = I::Item; default fn new(iter: I) -> Self { Enumerate { iter, count: 0, len: 0, // unused } } #[inline] default fn next(&mut self) -> Option<(usize, I::Item)> { let a = self.iter.next()?; let i = self.count; // Possible undefined overflow. self.count += 1; Some((i, a)) } } impl<I> EnumerateImpl<I> for Enumerate<I> where I: std::iter::TrustedLen + ExactSizeIterator + Iterator, { fn new(iter: I) -> Self { let len = iter.size_hint().0; Enumerate { iter, count: 0, len, } } #[inline] fn next(&mut self) -> Option<(usize, I::Item)> { let a = self.iter.next()?; unsafe { std::intrinsics::assume(self.count < self.len); } let i = self.count; // Possible undefined overflow. self.count += 1; Some((i, a)) } }
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