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Chris Lattner23d7b362006-10-29 23:42:03 +00001//===--- CStringMap.cpp - CString Hash table map implementation -----------===//
2//
3// The LLVM Compiler Infrastructure
4//
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.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements the CStringMap class.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/ADT/CStringMap.h"
15#include <cassert>
16using namespace llvm;
17
18CStringMapVisitor::~CStringMapVisitor() {
19}
20
21CStringMapImpl::CStringMapImpl(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;
25 ItemSize = itemSize;
26 NumItems = 0;
27
28 TheTable = new ItemBucket[NumBuckets]();
29 memset(TheTable, 0, NumBuckets*sizeof(ItemBucket));
30}
31
32
33/// HashString - Compute a hash code for the specified string.
34///
35static unsigned HashString(const char *Start, const char *End) {
Chris Lattner38742b92007-01-06 23:19:38 +000036 // Bernstein hash function.
Chris Lattner23d7b362006-10-29 23:42:03 +000037 unsigned int Result = 0;
Chris Lattner38742b92007-01-06 23:19:38 +000038 // TODO: investigate whether a modified bernstein hash function performs
Chris Lattner41a44292007-01-06 23:20:51 +000039 // better: http://eternallyconfuzzled.com/tuts/algorithms/jsw_tut_hashing.aspx
Chris Lattner38742b92007-01-06 23:19:38 +000040 // X*33+c -> X*33^c
Chris Lattner23d7b362006-10-29 23:42:03 +000041 while (Start != End)
42 Result = Result * 33 + *Start++;
43 Result = Result + (Result >> 5);
44 return Result;
45}
46
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
51/// of the string.
52unsigned CStringMapImpl::LookupBucketFor(const char *NameStart,
53 const char *NameEnd) {
54 unsigned HTSize = NumBuckets;
55 unsigned FullHashValue = HashString(NameStart, NameEnd);
56 unsigned BucketNo = FullHashValue & (HTSize-1);
57
58 unsigned ProbeAmt = 1;
59 while (1) {
60 ItemBucket &Bucket = TheTable[BucketNo];
Chris Lattneree182422007-02-08 19:08:37 +000061 StringMapEntryBase *BucketItem = Bucket.Item;
Chris Lattner23d7b362006-10-29 23:42:03 +000062 // If we found an empty bucket, this key isn't in the table yet, return it.
63 if (BucketItem == 0) {
64 Bucket.FullHashValue = FullHashValue;
65 return BucketNo;
66 }
67
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
74 // null-terminated!
75 char *ItemStr = (char*)BucketItem+ItemSize;
Chris Lattneree182422007-02-08 19:08:37 +000076 unsigned ItemStrLen = BucketItem->getKeyLength();
77 if (unsigned(NameEnd-NameStart) == ItemStrLen &&
78 memcmp(ItemStr, NameStart, ItemStrLen) == 0) {
Chris Lattner23d7b362006-10-29 23:42:03 +000079 // We found a match!
80 return BucketNo;
81 }
82 }
83
84 // Okay, we didn't find the item. Probe to the next bucket.
85 BucketNo = (BucketNo+ProbeAmt) & (HTSize-1);
86
87 // Use quadratic probing, it has fewer clumping artifacts than linear
88 // probing and has good cache behavior in the common case.
89 ++ProbeAmt;
90 }
91}
92
93/// RehashTable - Grow the table, redistributing values into the buckets with
94/// the appropriate mod-of-hashtable-size.
95void CStringMapImpl::RehashTable() {
96 unsigned NewSize = NumBuckets*2;
97 ItemBucket *NewTableArray = new ItemBucket[NewSize]();
98 memset(NewTableArray, 0, NewSize*sizeof(ItemBucket));
99
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) {
103 if (IB->Item) {
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;
110 continue;
111 }
112
113 unsigned ProbeSize = 1;
114 do {
115 NewBucket = (NewBucket + ProbeSize++) & (NewSize-1);
116 } while (NewTableArray[NewBucket].Item);
117
118 // Finally found a slot. Fill it in.
119 NewTableArray[NewBucket].Item = IB->Item;
120 NewTableArray[NewBucket].FullHashValue = FullHash;
121 }
122 }
123
124 delete[] TheTable;
125
126 TheTable = NewTableArray;
127 NumBuckets = NewSize;
128}
129
130
131/// VisitEntries - This method walks through all of the items,
132/// invoking Visitor.Visit for each of them.
133void CStringMapImpl::VisitEntries(const CStringMapVisitor &Visitor) const {
134 for (ItemBucket *IB = TheTable, *E = TheTable+NumBuckets; IB != E; ++IB) {
Chris Lattneree182422007-02-08 19:08:37 +0000135 if (StringMapEntryBase *Id = IB->Item)
Chris Lattner23d7b362006-10-29 23:42:03 +0000136 Visitor.Visit((char*)Id + ItemSize, Id);
137 }
138}