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runtime: tighten select permutation generation

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This is the optimization made to math/rand in CL 21030043.

Change-Id: I231b24fa77cac1fe74ba887db76313b5efaab3e8
Reviewed-on: https://go-review.googlesource.com/9269
Reviewed-by: Minux Ma <minux@golang.org>
This commit is contained in:
Josh Bleecher Snyder 2014-12-18 11:48:39 -08:00
parent 3787950a92
commit fd5540e7e5
1 changed files with 1 additions and 5 deletions
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6
src/runtime/select.go
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@ -244,13 +244,9 @@ func selectgoImpl(sel *hselect) (uintptr, uint16) {
pollslice := slice{unsafe.Pointer(sel.pollorder), int(sel.ncase), int(sel.ncase)}
pollorder := *(*[]uint16)(unsafe.Pointer(&pollslice))
for i := 0; i < int(sel.ncase); i++ {
pollorder[i] = uint16(i)
}
for i := 1; i < int(sel.ncase); i++ {
o := pollorder[i]
j := int(fastrand1()) % (i + 1)
pollorder[i] = pollorder[j]
pollorder[j] = o
pollorder[j] = uint16(i)
}
// sort the cases by Hchan address to get the locking order.