StringMap.cpp revision 23d7b3611759c7fb3a853dfce3ee3d43ef5ca67d 
1//===--- 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) {
36  unsigned int Result = 0;
37  // Perl hash function.
38  while (Start != End)
39    Result = Result * 33 + *Start++;
40  Result = Result + (Result >> 5);
41  return Result;
42}
43
44/// LookupBucketFor - Look up the bucket that the specified string should end
45/// up in.  If it already exists as a key in the map, the Item pointer for the
46/// specified bucket will be non-null.  Otherwise, it will be null.  In either
47/// case, the FullHashValue field of the bucket will be set to the hash value
48/// of the string.
49unsigned CStringMapImpl::LookupBucketFor(const char *NameStart,
50                                         const char *NameEnd) {
51  unsigned HTSize = NumBuckets;
52  unsigned FullHashValue = HashString(NameStart, NameEnd);
53  unsigned BucketNo = FullHashValue & (HTSize-1);
54
55  unsigned ProbeAmt = 1;
56  while (1) {
57    ItemBucket &Bucket = TheTable[BucketNo];
58    void *BucketItem = Bucket.Item;
59    // If we found an empty bucket, this key isn't in the table yet, return it.
60    if (BucketItem == 0) {
61      Bucket.FullHashValue = FullHashValue;
62      return BucketNo;
63    }
64
65    // If the full hash value matches, check deeply for a match.  The common
66    // case here is that we are only looking at the buckets (for item info
67    // being non-null and for the full hash value) not at the items.  This
68    // is important for cache locality.
69    if (Bucket.FullHashValue == FullHashValue) {
70      // Do the comparison like this because NameStart isn't necessarily
71      // null-terminated!
72      char *ItemStr = (char*)BucketItem+ItemSize;
73      if (strlen(ItemStr) == unsigned(NameEnd-NameStart) &&
74          memcmp(ItemStr, NameStart, (NameEnd-NameStart)) == 0) {
75        // We found a match!
76        return BucketNo;
77      }
78    }
79
80    // Okay, we didn't find the item.  Probe to the next bucket.
81    BucketNo = (BucketNo+ProbeAmt) & (HTSize-1);
82
83    // Use quadratic probing, it has fewer clumping artifacts than linear
84    // probing and has good cache behavior in the common case.
85    ++ProbeAmt;
86  }
87}
88
89/// RehashTable - Grow the table, redistributing values into the buckets with
90/// the appropriate mod-of-hashtable-size.
91void CStringMapImpl::RehashTable() {
92  unsigned NewSize = NumBuckets*2;
93  ItemBucket *NewTableArray = new ItemBucket[NewSize]();
94  memset(NewTableArray, 0, NewSize*sizeof(ItemBucket));
95
96  // Rehash all the items into their new buckets.  Luckily :) we already have
97  // the hash values available, so we don't have to rehash any strings.
98  for (ItemBucket *IB = TheTable, *E = TheTable+NumBuckets; IB != E; ++IB) {
99    if (IB->Item) {
100      // Fast case, bucket available.
101      unsigned FullHash = IB->FullHashValue;
102      unsigned NewBucket = FullHash & (NewSize-1);
103      if (NewTableArray[NewBucket].Item == 0) {
104        NewTableArray[FullHash & (NewSize-1)].Item = IB->Item;
105        NewTableArray[FullHash & (NewSize-1)].FullHashValue = FullHash;
106        continue;
107      }
108
109      unsigned ProbeSize = 1;
110      do {
111        NewBucket = (NewBucket + ProbeSize++) & (NewSize-1);
112      } while (NewTableArray[NewBucket].Item);
113
114      // Finally found a slot.  Fill it in.
115      NewTableArray[NewBucket].Item = IB->Item;
116      NewTableArray[NewBucket].FullHashValue = FullHash;
117    }
118  }
119
120  delete[] TheTable;
121
122  TheTable = NewTableArray;
123  NumBuckets = NewSize;
124}
125
126
127/// VisitEntries - This method walks through all of the items,
128/// invoking Visitor.Visit for each of them.
129void CStringMapImpl::VisitEntries(const CStringMapVisitor &Visitor) const {
130  for (ItemBucket *IB = TheTable, *E = TheTable+NumBuckets; IB != E; ++IB) {
131    if (void *Id = IB->Item)
132      Visitor.Visit((char*)Id + ItemSize, Id);
133  }
134}
135