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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45418 91177308-0d34-0410-b5e6-96231b3b80d8
235 lines
8.3 KiB
C++
235 lines
8.3 KiB
C++
//===--- StringMap.cpp - String Hash table map implementation -------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the StringMap class.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/StringMap.h"
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#include <cassert>
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using namespace llvm;
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StringMapImpl::StringMapImpl(unsigned InitSize, unsigned itemSize) {
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ItemSize = itemSize;
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// If a size is specified, initialize the table with that many buckets.
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if (InitSize) {
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init(InitSize);
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return;
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}
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// Otherwise, initialize it with zero buckets to avoid the allocation.
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TheTable = 0;
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NumBuckets = 0;
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NumItems = 0;
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NumTombstones = 0;
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}
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void StringMapImpl::init(unsigned InitSize) {
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assert((InitSize & (InitSize-1)) == 0 &&
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"Init Size must be a power of 2 or zero!");
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NumBuckets = InitSize ? InitSize : 16;
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NumItems = 0;
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NumTombstones = 0;
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TheTable = (ItemBucket*)calloc(NumBuckets+1, sizeof(ItemBucket));
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// Allocate one extra bucket, set it to look filled so the iterators stop at
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// end.
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TheTable[NumBuckets].Item = (StringMapEntryBase*)2;
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}
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/// HashString - Compute a hash code for the specified string.
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///
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static unsigned HashString(const char *Start, const char *End) {
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// Bernstein hash function.
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unsigned int Result = 0;
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// TODO: investigate whether a modified bernstein hash function performs
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// better: http://eternallyconfuzzled.com/tuts/algorithms/jsw_tut_hashing.aspx
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// X*33+c -> X*33^c
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while (Start != End)
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Result = Result * 33 + *Start++;
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Result = Result + (Result >> 5);
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return Result;
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}
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/// LookupBucketFor - Look up the bucket that the specified string should end
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/// up in. If it already exists as a key in the map, the Item pointer for the
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/// specified bucket will be non-null. Otherwise, it will be null. In either
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/// case, the FullHashValue field of the bucket will be set to the hash value
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/// of the string.
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unsigned StringMapImpl::LookupBucketFor(const char *NameStart,
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const char *NameEnd) {
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unsigned HTSize = NumBuckets;
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if (HTSize == 0) { // Hash table unallocated so far?
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init(16);
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HTSize = NumBuckets;
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}
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unsigned FullHashValue = HashString(NameStart, NameEnd);
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unsigned BucketNo = FullHashValue & (HTSize-1);
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unsigned ProbeAmt = 1;
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int FirstTombstone = -1;
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while (1) {
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ItemBucket &Bucket = TheTable[BucketNo];
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StringMapEntryBase *BucketItem = Bucket.Item;
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// If we found an empty bucket, this key isn't in the table yet, return it.
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if (BucketItem == 0) {
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// If we found a tombstone, we want to reuse the tombstone instead of an
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// empty bucket. This reduces probing.
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if (FirstTombstone != -1) {
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TheTable[FirstTombstone].FullHashValue = FullHashValue;
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return FirstTombstone;
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}
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Bucket.FullHashValue = FullHashValue;
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return BucketNo;
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}
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if (BucketItem == getTombstoneVal()) {
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// Skip over tombstones. However, remember the first one we see.
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if (FirstTombstone == -1) FirstTombstone = BucketNo;
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} else if (Bucket.FullHashValue == FullHashValue) {
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// If the full hash value matches, check deeply for a match. The common
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// case here is that we are only looking at the buckets (for item info
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// being non-null and for the full hash value) not at the items. This
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// is important for cache locality.
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// Do the comparison like this because NameStart isn't necessarily
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// null-terminated!
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char *ItemStr = (char*)BucketItem+ItemSize;
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unsigned ItemStrLen = BucketItem->getKeyLength();
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if (unsigned(NameEnd-NameStart) == ItemStrLen &&
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memcmp(ItemStr, NameStart, ItemStrLen) == 0) {
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// We found a match!
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return BucketNo;
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}
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}
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// Okay, we didn't find the item. Probe to the next bucket.
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BucketNo = (BucketNo+ProbeAmt) & (HTSize-1);
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// Use quadratic probing, it has fewer clumping artifacts than linear
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// probing and has good cache behavior in the common case.
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++ProbeAmt;
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}
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}
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/// FindKey - Look up the bucket that contains the specified key. If it exists
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/// in the map, return the bucket number of the key. Otherwise return -1.
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/// This does not modify the map.
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int StringMapImpl::FindKey(const char *KeyStart, const char *KeyEnd) const {
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unsigned HTSize = NumBuckets;
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if (HTSize == 0) return -1; // Really empty table?
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unsigned FullHashValue = HashString(KeyStart, KeyEnd);
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unsigned BucketNo = FullHashValue & (HTSize-1);
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unsigned ProbeAmt = 1;
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while (1) {
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ItemBucket &Bucket = TheTable[BucketNo];
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StringMapEntryBase *BucketItem = Bucket.Item;
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// If we found an empty bucket, this key isn't in the table yet, return.
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if (BucketItem == 0)
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return -1;
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if (BucketItem == getTombstoneVal()) {
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// Ignore tombstones.
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} else if (Bucket.FullHashValue == FullHashValue) {
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// If the full hash value matches, check deeply for a match. The common
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// case here is that we are only looking at the buckets (for item info
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// being non-null and for the full hash value) not at the items. This
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// is important for cache locality.
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// Do the comparison like this because NameStart isn't necessarily
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// null-terminated!
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char *ItemStr = (char*)BucketItem+ItemSize;
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unsigned ItemStrLen = BucketItem->getKeyLength();
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if (unsigned(KeyEnd-KeyStart) == ItemStrLen &&
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memcmp(ItemStr, KeyStart, ItemStrLen) == 0) {
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// We found a match!
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return BucketNo;
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}
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}
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// Okay, we didn't find the item. Probe to the next bucket.
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BucketNo = (BucketNo+ProbeAmt) & (HTSize-1);
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// Use quadratic probing, it has fewer clumping artifacts than linear
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// probing and has good cache behavior in the common case.
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++ProbeAmt;
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}
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}
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/// RemoveKey - Remove the specified StringMapEntry from the table, but do not
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/// delete it. This aborts if the value isn't in the table.
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void StringMapImpl::RemoveKey(StringMapEntryBase *V) {
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const char *VStr = (char*)V + ItemSize;
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StringMapEntryBase *V2 = RemoveKey(VStr, VStr+V->getKeyLength());
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V2 = V2;
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assert(V == V2 && "Didn't find key?");
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}
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/// RemoveKey - Remove the StringMapEntry for the specified key from the
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/// table, returning it. If the key is not in the table, this returns null.
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StringMapEntryBase *StringMapImpl::RemoveKey(const char *KeyStart,
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const char *KeyEnd) {
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int Bucket = FindKey(KeyStart, KeyEnd);
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if (Bucket == -1) return 0;
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StringMapEntryBase *Result = TheTable[Bucket].Item;
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TheTable[Bucket].Item = getTombstoneVal();
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--NumItems;
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++NumTombstones;
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return Result;
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}
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/// RehashTable - Grow the table, redistributing values into the buckets with
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/// the appropriate mod-of-hashtable-size.
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void StringMapImpl::RehashTable() {
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unsigned NewSize = NumBuckets*2;
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// Allocate one extra bucket which will always be non-empty. This allows the
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// iterators to stop at end.
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ItemBucket *NewTableArray =(ItemBucket*)calloc(NewSize+1, sizeof(ItemBucket));
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NewTableArray[NewSize].Item = (StringMapEntryBase*)2;
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// Rehash all the items into their new buckets. Luckily :) we already have
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// the hash values available, so we don't have to rehash any strings.
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for (ItemBucket *IB = TheTable, *E = TheTable+NumBuckets; IB != E; ++IB) {
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if (IB->Item && IB->Item != getTombstoneVal()) {
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// Fast case, bucket available.
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unsigned FullHash = IB->FullHashValue;
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unsigned NewBucket = FullHash & (NewSize-1);
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if (NewTableArray[NewBucket].Item == 0) {
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NewTableArray[FullHash & (NewSize-1)].Item = IB->Item;
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NewTableArray[FullHash & (NewSize-1)].FullHashValue = FullHash;
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continue;
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}
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// Otherwise probe for a spot.
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unsigned ProbeSize = 1;
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do {
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NewBucket = (NewBucket + ProbeSize++) & (NewSize-1);
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} while (NewTableArray[NewBucket].Item);
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// Finally found a slot. Fill it in.
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NewTableArray[NewBucket].Item = IB->Item;
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NewTableArray[NewBucket].FullHashValue = FullHash;
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}
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}
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free(TheTable);
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TheTable = NewTableArray;
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NumBuckets = NewSize;
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}
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