775896 - OrderedHashTable should have a hashShift field like HashTable

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jason Orendorff [:jorendorff]]

The hashing scheme of js::HashTable uses the most significant bits of a prepared hash code to select a hash bucket.  js::OrderedHashTable uses the least significant bits, which is very bad.

Comment 1

[Jason Orendorff [:jorendorff]]

Attachment: v1

Comment 2

[Jason Orendorff [:jorendorff]]

A quick note on this patch:
>-  if (hashTableMask > initialBuckets() && liveCount < dataLength * minDataFill()) {
>+  if (hashBuckets() > initialBuckets() && liveCount < dataLength * minDataFill()) {

This changes the behavior, because hashTableMask is the number of buckets minus one.

The old behavior was accidental--a bug, but harmless as long as initialBuckets() was more than 1.

Comment 3

[Jason Orendorff [:jorendorff]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/0610488a81c9

Comment 4

[Ed Morley [:emorley]]

https://hg.mozilla.org/mozilla-central/rev/0610488a81c9