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Do some cleanups for hashmaps #45263

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Merged
merged 2 commits into from
Oct 15, 2017
Merged

Do some cleanups for hashmaps #45263

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bb9e850
std: Get rid of hash_offet in RawTable
Manishearth Oct 13, 2017
e8e7715
std: Set probe length tag on cloned hashmaps
Manishearth Oct 13, 2017
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32 changes: 16 additions & 16 deletions src/libstd/collections/hash/table.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -717,26 +717,25 @@ fn calculate_offsets(hashes_size: usize,
(pairs_offset, end_of_pairs, oflo)
}

// Returns a tuple of (minimum required malloc alignment, hash_offset,
// Returns a tuple of (minimum required malloc alignment,
// array_size), from the start of a mallocated array.
fn calculate_allocation(hash_size: usize,
hash_align: usize,
pairs_size: usize,
pairs_align: usize)
-> (usize, usize, usize, bool) {
let hash_offset = 0;
-> (usize, usize, bool) {
let (_, end_of_pairs, oflo) = calculate_offsets(hash_size, pairs_size, pairs_align);

let align = cmp::max(hash_align, pairs_align);

(align, hash_offset, end_of_pairs, oflo)
(align, end_of_pairs, oflo)
}

#[test]
fn test_offset_calculation() {
assert_eq!(calculate_allocation(128, 8, 16, 8), (8, 0, 144, false));
assert_eq!(calculate_allocation(3, 1, 2, 1), (1, 0, 5, false));
assert_eq!(calculate_allocation(6, 2, 12, 4), (4, 0, 20, false));
assert_eq!(calculate_allocation(128, 8, 16, 8), (8, 144, false));
assert_eq!(calculate_allocation(3, 1, 2, 1), (1, 5, false));
assert_eq!(calculate_allocation(6, 2, 12, 4), (4, 20, false));
assert_eq!(calculate_offsets(128, 15, 4), (128, 143, false));
assert_eq!(calculate_offsets(3, 2, 4), (4, 6, false));
assert_eq!(calculate_offsets(6, 12, 4), (8, 20, false));
Expand Down Expand Up @@ -768,10 +767,10 @@ impl<K, V> RawTable<K, V> {
// This is great in theory, but in practice getting the alignment
// right is a little subtle. Therefore, calculating offsets has been
// factored out into a different function.
let (alignment, hash_offset, size, oflo) = calculate_allocation(hashes_size,
align_of::<HashUint>(),
pairs_size,
align_of::<(K, V)>());
let (alignment, size, oflo) = calculate_allocation(hashes_size,
align_of::<HashUint>(),
pairs_size,
align_of::<(K, V)>());
assert!(!oflo, "capacity overflow");

// One check for overflow that covers calculation and rounding of size.
Expand All @@ -784,7 +783,7 @@ impl<K, V> RawTable<K, V> {
let buffer = Heap.alloc(Layout::from_size_align(size, alignment).unwrap())
.unwrap_or_else(|e| Heap.oom(e));

let hashes = buffer.offset(hash_offset as isize) as *mut HashUint;
let hashes = buffer as *mut HashUint;

RawTable {
capacity_mask: capacity.wrapping_sub(1),
Expand Down Expand Up @@ -1157,6 +1156,7 @@ impl<K: Clone, V: Clone> Clone for RawTable<K, V> {
}

new_ht.size = self.size();
new_ht.set_tag(self.tag());
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Good point, I overlooked that before.


new_ht
}
Expand All @@ -1183,10 +1183,10 @@ unsafe impl<#[may_dangle] K, #[may_dangle] V> Drop for RawTable<K, V> {

let hashes_size = self.capacity() * size_of::<HashUint>();
let pairs_size = self.capacity() * size_of::<(K, V)>();
let (align, _, size, oflo) = calculate_allocation(hashes_size,
align_of::<HashUint>(),
pairs_size,
align_of::<(K, V)>());
let (align, size, oflo) = calculate_allocation(hashes_size,
align_of::<HashUint>(),
pairs_size,
align_of::<(K, V)>());

debug_assert!(!oflo, "should be impossible");

Expand Down