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runtime: use integer math for hashmap overLoadFactor

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Change-Id: I92cf39a05e738a03d956779d7a1ab1ef8074b2ab
Reviewed-on: https://go-review.googlesource.com/54655
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Josh Bleecher Snyder 2017-07-16 17:37:27 -10:00
parent 694875cbf2
commit 733567a186
2 changed files with 6 additions and 5 deletions
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9
src/runtime/hashmap.go
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@ -64,8 +64,10 @@ const (
bucketCntBits = 3
bucketCnt = 1 << bucketCntBits
// Maximum average load of a bucket that triggers growth.
loadFactor = 6.5
// Maximum average load of a bucket that triggers growth is 6.5.
// Represent as loadFactorNum/loadFactDen, to allow integer math.
loadFactorNum = 13
loadFactorDen = 2
// Maximum key or value size to keep inline (instead of mallocing per element).
// Must fit in a uint8.
@ -984,8 +986,7 @@ func hashGrow(t *maptype, h *hmap) {
// overLoadFactor reports whether count items placed in 1<<B buckets is over loadFactor.
func overLoadFactor(count int64, B uint8) bool {
// TODO: rewrite to use integer math and comparison?
return count >= bucketCnt && float32(count) >= loadFactor*float32((uint64(1)<<B))
return count >= bucketCnt && uint64(count) >= loadFactorNum*((uint64(1)<<B)/loadFactorDen)
}
// tooManyOverflowBuckets reports whether noverflow buckets is too many for a map with 1<<B buckets.

2
src/runtime/stubs.go
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@ -91,7 +91,7 @@ func reflect_memmove(to, from unsafe.Pointer, n uintptr) {
}
// exported value for testing
var hashLoad = loadFactor
var hashLoad = float32(loadFactorNum) / float32(loadFactorDen)
//go:nosplit
func fastrand() uint32 {