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135 lines
4.7 KiB
C++
135 lines
4.7 KiB
C++
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//===--- CStringMap.cpp - CString 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 was developed by Chris Lattner and is distributed under
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// the University of Illinois Open Source 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 CStringMap class.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/CStringMap.h"
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#include <cassert>
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using namespace llvm;
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CStringMapVisitor::~CStringMapVisitor() {
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}
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CStringMapImpl::CStringMapImpl(unsigned InitSize, unsigned itemSize) {
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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 : 512;
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ItemSize = itemSize;
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NumItems = 0;
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TheTable = new ItemBucket[NumBuckets]();
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memset(TheTable, 0, NumBuckets*sizeof(ItemBucket));
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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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unsigned int Result = 0;
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// Perl hash function.
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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 CStringMapImpl::LookupBucketFor(const char *NameStart,
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const char *NameEnd) {
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unsigned HTSize = NumBuckets;
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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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while (1) {
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ItemBucket &Bucket = TheTable[BucketNo];
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void *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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Bucket.FullHashValue = FullHashValue;
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return BucketNo;
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}
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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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if (Bucket.FullHashValue == FullHashValue) {
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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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if (strlen(ItemStr) == unsigned(NameEnd-NameStart) &&
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memcmp(ItemStr, NameStart, (NameEnd-NameStart)) == 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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/// 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 CStringMapImpl::RehashTable() {
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unsigned NewSize = NumBuckets*2;
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ItemBucket *NewTableArray = new ItemBucket[NewSize]();
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memset(NewTableArray, 0, NewSize*sizeof(ItemBucket));
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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) {
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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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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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delete[] TheTable;
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TheTable = NewTableArray;
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NumBuckets = NewSize;
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}
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/// VisitEntries - This method walks through all of the items,
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/// invoking Visitor.Visit for each of them.
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void CStringMapImpl::VisitEntries(const CStringMapVisitor &Visitor) const {
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for (ItemBucket *IB = TheTable, *E = TheTable+NumBuckets; IB != E; ++IB) {
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if (void *Id = IB->Item)
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Visitor.Visit((char*)Id + ItemSize, Id);
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}
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}
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