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[backport] pseudorandom probing for hash collision (#13418)

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Timothee Cour 2020-02-19 08:19:55 -08:00 • committed by GitHub
commit 8c22518d67
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12 changed files with 258 additions and 178 deletions
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6
lib/pure/collections/sharedtables.nim
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@ -25,6 +25,7 @@ type
SharedTable*[A, B] = object ## generic hash SharedTable
data: KeyValuePairSeq[A, B]
counter, dataLen: int
countDeleted: int
lock: Lock
template maxHash(t): untyped = t.dataLen-1
@ -32,7 +33,7 @@ template maxHash(t): untyped = t.dataLen-1
include tableimpl
template st_maybeRehashPutImpl(enlarge) {.dirty.} =
if mustRehash(t.dataLen, t.counter):
if mustRehash(t):
enlarge(t)
index = rawGetKnownHC(t, key, hc)
index = -1 - index # important to transform for mgetOrPutImpl
@ -49,9 +50,10 @@ proc enlarge[A, B](t: var SharedTable[A, B]) =
for i in 0..<oldSize:
let eh = n[i].hcode
if isFilled(eh):
var perturb = t.getPerturb(eh)
var j: Hash = eh and maxHash(t)
while isFilled(t.data[j].hcode):
j = nextTry(j, maxHash(t))
j = nextTry(j, maxHash(t), perturb)
rawInsert(t, t.data, n[i].key, n[i].val, eh, j)
deallocShared(n)