Details
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Enhancement
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Resolution: Fixed
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P4
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8
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b103
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generic
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generic
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Not verified
Backports
Issue | Fix Version | Assignee | Priority | Status | Resolution | Resolved In Build |
---|---|---|---|---|---|---|
JDK-8034602 | 7u65 | Ivan Gerasimov | P4 | Resolved | Fixed | b01 |
JDK-8022950 | 7u60 | Ivan Gerasimov | P4 | Closed | Fixed | b01 |
Description
This is a SUNBUG for 100189: https://bugs.openjdk.java.net/show_bug.cgi?id=100189
Constructor does this:
public HashMap(int initialCapacity, float loadFactor) {
...
int capacity = 1;
while (capacity < initialCapacity)
capacity <<= 1;
...
}
It is magnitude+ faster to do this:
static final double LOG2 = Math.log(2.0);
public HashMap(int initialCapacity, float loadFactor) {
...
int capacity = 1 << ((int)Math.ceil(Math.log(initialCapacity)/LOG2 ));
...
}
Given the error checking in the head of the constructor, this code should just
plug-in.
Constructor does this:
public HashMap(int initialCapacity, float loadFactor) {
...
int capacity = 1;
while (capacity < initialCapacity)
capacity <<= 1;
...
}
It is magnitude+ faster to do this:
static final double LOG2 = Math.log(2.0);
public HashMap(int initialCapacity, float loadFactor) {
...
int capacity = 1 << ((int)Math.ceil(Math.log(initialCapacity)/LOG2 ));
...
}
Given the error checking in the head of the constructor, this code should just
plug-in.
Attachments
Issue Links
- backported by
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JDK-8034602 (coll) Inefficient calculation of power of two in HashMap
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- Resolved
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JDK-8022950 (coll) Inefficient calculation of power of two in HashMap
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- Closed
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