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llvm-6502/lib/Support/StringMap.cpp
2007-12-29 20:36:04 +00:00

235 lines
8.3 KiB
C++

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