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Implement extend_from_slice and insert_from_slice with memmove optimization #29

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Merged
merged 4 commits into from
Jan 25, 2017
Merged

Implement extend_from_slice and insert_from_slice with memmove optimization #29

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22bbcd2
Implement extend_slice and insert_slice with memcpy optimization
nipunn1313 Aug 23, 2016
e6e67cd
Rename to extend_from_slice and insert_from_slice
nipunn1313 Aug 24, 2016
0fe867e
Add benchmark for extend_from_slice
nipunn1313 Aug 27, 2016
aef2113
Add bench insert_from_slice
nipunn1313 Sep 12, 2016
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21 changes: 21 additions & 0 deletions benches/bench.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -63,6 +63,27 @@ fn bench_extend(b: &mut Bencher) {
});
}

#[bench]
fn bench_extend_from_slice(b: &mut Bencher) {
let v: Vec<u64> = (0..100).collect();
b.iter(|| {
let mut vec: SmallVec<[u64; 16]> = SmallVec::new();
vec.extend_from_slice(&v);
vec
});
}

#[bench]
fn bench_insert_from_slice(b: &mut Bencher) {
let v: Vec<u64> = (0..100).collect();
b.iter(|| {
let mut vec: SmallVec<[u64; 16]> = SmallVec::new();
vec.insert_from_slice(0, &v);
vec.insert_from_slice(0, &v);
vec
});
}

#[bench]
fn bench_pushpop(b: &mut Bencher) {
#[inline(never)]
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45 changes: 45 additions & 0 deletions lib.rs
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Expand Up @@ -477,6 +477,29 @@ impl<A: Array> SmallVec<A> {
}
}

impl<A: Array> SmallVec<A> where A::Item: Copy {
pub fn insert_from_slice(&mut self, index: usize, slice: &[A::Item]) {
self.reserve(slice.len());
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Hmm... I'm kind of sleepy right now, but I think here you should reserve index + slice.len()?

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I believe reserve takes in an "additional" amount required and ensures the capacity is large enough, so I think this is ok.

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Oh, you're right, nvm, I thought reserve() did the usual stuff, that is, ensuring capacity.


let len = self.len;
assert!(index <= len);

unsafe {
let slice_ptr = slice.as_ptr();
let ptr = self.as_mut_ptr().offset(index as isize);
ptr::copy(ptr, ptr.offset(slice.len() as isize), len - index);
ptr::copy(slice_ptr, ptr, slice.len());
self.set_len(len + slice.len());
}
}

#[inline]
pub fn extend_from_slice(&mut self, slice: &[A::Item]) {
let len = self.len();
self.insert_from_slice(len, slice);
}
}

impl<A: Array> ops::Deref for SmallVec<A> {
type Target = [A::Item];
#[inline]
Expand Down Expand Up @@ -1068,6 +1091,28 @@ pub mod tests {
v.grow(5);
}

#[test]
fn test_insert_from_slice() {
let mut v: SmallVec<[u8; 8]> = SmallVec::new();
for x in 0..4 {
v.push(x);
}
assert_eq!(v.len(), 4);
v.insert_from_slice(1, &[5, 6]);
assert_eq!(&v.iter().map(|v| *v).collect::<Vec<_>>(), &[0, 5, 6, 1, 2, 3]);
}

#[test]
fn test_extend_from_slice() {
let mut v: SmallVec<[u8; 8]> = SmallVec::new();
for x in 0..4 {
v.push(x);
}
assert_eq!(v.len(), 4);
v.extend_from_slice(&[5, 6]);
assert_eq!(&v.iter().map(|v| *v).collect::<Vec<_>>(), &[0, 1, 2, 3, 5, 6]);
}

#[test]
#[should_panic]
fn test_drop_panic_smallvec() {
Expand Down