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Implement TrustedRandomAccess for slice::{Chunks, ChunksMut, Windows} #47142

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Merged
merged 4 commits into from
Jan 5, 2018
Merged

Implement TrustedRandomAccess for slice::{Chunks, ChunksMut, Windows} #47142

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48f2f71
Implement TrustedRandomAccess for slice::{Chunks, ChunksMut, Windows}
sdroege Jan 2, 2018
a56a3fc
Add unit test for zipping slice::{Chunks, ChunksMut, Windows} iterators
sdroege Jan 3, 2018
3f29e2b
Fix compilation of TrustedRandomAccess impl for slice::Chunks
sdroege Jan 3, 2018
b69c124
Fix potential overflow in TrustedRandomAccess impl for slice::{Chunks…
sdroege Jan 4, 2018
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28 changes: 28 additions & 0 deletions src/libcore/slice/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2117,6 +2117,14 @@ impl<'a, T> ExactSizeIterator for Windows<'a, T> {}
#[unstable(feature = "fused", issue = "35602")]
impl<'a, T> FusedIterator for Windows<'a, T> {}

#[doc(hidden)]
unsafe impl<'a, T> TrustedRandomAccess for Windows<'a, T> {
unsafe fn get_unchecked(&mut self, i: usize) -> &'a [T] {
from_raw_parts(self.v.as_ptr().offset(i as isize), self.size)
}
fn may_have_side_effect() -> bool { false }
}

/// An iterator over a slice in (non-overlapping) chunks (`chunk_size` elements at a
/// time).
///
Expand Down Expand Up @@ -2228,6 +2236,16 @@ impl<'a, T> ExactSizeIterator for Chunks<'a, T> {}
#[unstable(feature = "fused", issue = "35602")]
impl<'a, T> FusedIterator for Chunks<'a, T> {}

#[doc(hidden)]
unsafe impl<'a, T> TrustedRandomAccess for Chunks<'a, T> {
unsafe fn get_unchecked(&mut self, i: usize) -> &'a [T] {
let start = i * self.chunk_size;
let end = cmp::min(start + self.chunk_size, self.v.len());
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@bluss bluss Jan 3, 2018 •
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There is a potential wraparound here isn't there? i is in bounds but start + size can still wrap around. In particular for [(); !0].chunks((!0)/2 +1) I think.

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It turns out Rust ICES on that array. For those that don't like my mobile-friendly syntax, !0 is the same as usize::max_value().

However Rust accepts a vec of this length, and we can demo (playground link)

fn main() {
    let v = vec![(); !0];
    let iter = v.chunks((!0)/2 +1);
    for elt in iter {
        println!("Found chunk of len {}", elt.len());
    }
}

Which has output:

Found chunk of len 9223372036854775808
Found chunk of len 9223372036854775807

from_raw_parts(self.v.as_ptr().offset(start as isize), end - start)
}
fn may_have_side_effect() -> bool { false }
}

/// An iterator over a slice in (non-overlapping) mutable chunks (`chunk_size`
/// elements at a time). When the slice len is not evenly divided by the chunk
/// size, the last slice of the iteration will be the remainder.
Expand Down Expand Up @@ -2331,6 +2349,16 @@ impl<'a, T> ExactSizeIterator for ChunksMut<'a, T> {}
#[unstable(feature = "fused", issue = "35602")]
impl<'a, T> FusedIterator for ChunksMut<'a, T> {}

#[doc(hidden)]
unsafe impl<'a, T> TrustedRandomAccess for ChunksMut<'a, T> {
unsafe fn get_unchecked(&mut self, i: usize) -> &'a mut [T] {
let start = i * self.chunk_size;
let end = cmp::min(start + self.chunk_size, self.v.len());
from_raw_parts_mut(self.v.as_mut_ptr().offset(start as isize), end - start)
}
fn may_have_side_effect() -> bool { false }
}

//
// Free functions
//
Expand Down
39 changes: 39 additions & 0 deletions src/libcore/tests/slice.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -137,6 +137,18 @@ fn test_chunks_last() {
assert_eq!(c2.last().unwrap()[0], 4);
}

#[test]
fn test_chunks_zip() {
let v1: &[i32] = &[0, 1, 2, 3, 4];
let v2: &[i32] = &[6, 7, 8, 9, 10];

let res = v1.chunks(2)
.zip(v2.chunks(2))
.map(|(a, b)| a.iter().sum::<i32>() + b.iter().sum::<i32>())
.collect::<Vec<_>>();
assert_eq!(res, vec![14, 22, 14]);
}

#[test]
fn test_chunks_mut_count() {
let v: &mut [i32] = &mut [0, 1, 2, 3, 4, 5];
Expand Down Expand Up @@ -176,6 +188,20 @@ fn test_chunks_mut_last() {
assert_eq!(c2.last().unwrap()[0], 4);
}

#[test]
fn test_chunks_mut_zip() {
let v1: &mut [i32] = &mut [0, 1, 2, 3, 4];
let v2: &[i32] = &[6, 7, 8, 9, 10];

for (a, b) in v1.chunks_mut(2).zip(v2.chunks(2)) {
let sum = b.iter().sum::<i32>();
for v in a {
*v += sum;
}
}
assert_eq!(v1, [13, 14, 19, 20, 14]);
}

#[test]
fn test_windows_count() {
let v: &[i32] = &[0, 1, 2, 3, 4, 5];
Expand Down Expand Up @@ -215,6 +241,19 @@ fn test_windows_last() {
assert_eq!(c2.last().unwrap()[0], 3);
}

#[test]
fn test_windows_zip() {
let v1: &[i32] = &[0, 1, 2, 3, 4];
let v2: &[i32] = &[6, 7, 8, 9, 10];

let res = v1.windows(2)
.zip(v2.windows(2))
.map(|(a, b)| a.iter().sum::<i32>() + b.iter().sum::<i32>())
.collect::<Vec<_>>();

assert_eq!(res, [14, 18, 22, 26]);
}

#[test]
fn get_range() {
let v: &[i32] = &[0, 1, 2, 3, 4, 5];
Expand Down