1 //===--- StringMap.cpp - String Hash table map implementation -------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by Chris Lattner and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the StringMap class.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/ADT/StringMap.h"
18 StringMapVisitor::~StringMapVisitor() {
21 StringMapImpl::StringMapImpl(unsigned InitSize, unsigned itemSize) {
22 assert((InitSize & (InitSize-1)) == 0 &&
23 "Init Size must be a power of 2 or zero!");
24 NumBuckets = InitSize ? InitSize : 512;
28 TheTable = new ItemBucket[NumBuckets]();
29 memset(TheTable, 0, NumBuckets*sizeof(ItemBucket));
33 /// HashString - Compute a hash code for the specified string.
35 static unsigned HashString(const char *Start, const char *End) {
36 // Bernstein hash function.
37 unsigned int Result = 0;
38 // TODO: investigate whether a modified bernstein hash function performs
39 // better: http://eternallyconfuzzled.com/tuts/algorithms/jsw_tut_hashing.aspx
42 Result = Result * 33 + *Start++;
43 Result = Result + (Result >> 5);
47 /// LookupBucketFor - Look up the bucket that the specified string should end
48 /// up in. If it already exists as a key in the map, the Item pointer for the
49 /// specified bucket will be non-null. Otherwise, it will be null. In either
50 /// case, the FullHashValue field of the bucket will be set to the hash value
52 unsigned StringMapImpl::LookupBucketFor(const char *NameStart,
53 const char *NameEnd) {
54 unsigned HTSize = NumBuckets;
55 unsigned FullHashValue = HashString(NameStart, NameEnd);
56 unsigned BucketNo = FullHashValue & (HTSize-1);
58 unsigned ProbeAmt = 1;
60 ItemBucket &Bucket = TheTable[BucketNo];
61 StringMapEntryBase *BucketItem = Bucket.Item;
62 // If we found an empty bucket, this key isn't in the table yet, return it.
63 if (BucketItem == 0) {
64 Bucket.FullHashValue = FullHashValue;
68 // If the full hash value matches, check deeply for a match. The common
69 // case here is that we are only looking at the buckets (for item info
70 // being non-null and for the full hash value) not at the items. This
71 // is important for cache locality.
72 if (Bucket.FullHashValue == FullHashValue) {
73 // Do the comparison like this because NameStart isn't necessarily
75 char *ItemStr = (char*)BucketItem+ItemSize;
76 unsigned ItemStrLen = BucketItem->getKeyLength();
77 if (unsigned(NameEnd-NameStart) == ItemStrLen &&
78 memcmp(ItemStr, NameStart, ItemStrLen) == 0) {
84 // Okay, we didn't find the item. Probe to the next bucket.
85 BucketNo = (BucketNo+ProbeAmt) & (HTSize-1);
87 // Use quadratic probing, it has fewer clumping artifacts than linear
88 // probing and has good cache behavior in the common case.
93 /// RehashTable - Grow the table, redistributing values into the buckets with
94 /// the appropriate mod-of-hashtable-size.
95 void StringMapImpl::RehashTable() {
96 unsigned NewSize = NumBuckets*2;
97 ItemBucket *NewTableArray = new ItemBucket[NewSize]();
98 memset(NewTableArray, 0, NewSize*sizeof(ItemBucket));
100 // Rehash all the items into their new buckets. Luckily :) we already have
101 // the hash values available, so we don't have to rehash any strings.
102 for (ItemBucket *IB = TheTable, *E = TheTable+NumBuckets; IB != E; ++IB) {
104 // Fast case, bucket available.
105 unsigned FullHash = IB->FullHashValue;
106 unsigned NewBucket = FullHash & (NewSize-1);
107 if (NewTableArray[NewBucket].Item == 0) {
108 NewTableArray[FullHash & (NewSize-1)].Item = IB->Item;
109 NewTableArray[FullHash & (NewSize-1)].FullHashValue = FullHash;
113 unsigned ProbeSize = 1;
115 NewBucket = (NewBucket + ProbeSize++) & (NewSize-1);
116 } while (NewTableArray[NewBucket].Item);
118 // Finally found a slot. Fill it in.
119 NewTableArray[NewBucket].Item = IB->Item;
120 NewTableArray[NewBucket].FullHashValue = FullHash;
126 TheTable = NewTableArray;
127 NumBuckets = NewSize;
131 /// VisitEntries - This method walks through all of the items,
132 /// invoking Visitor.Visit for each of them.
133 void StringMapImpl::VisitEntries(const StringMapVisitor &Visitor) const {
134 for (ItemBucket *IB = TheTable, *E = TheTable+NumBuckets; IB != E; ++IB) {
135 if (StringMapEntryBase *Id = IB->Item)
136 Visitor.Visit((char*)Id + ItemSize, Id);