add a highly efficient hash table that is specialized for mapping C strings
to some other type.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31286 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/CStringMap.cpp b/lib/Support/CStringMap.cpp
new file mode 100644
index 0000000..3229bfe
--- /dev/null
+++ b/lib/Support/CStringMap.cpp
@@ -0,0 +1,134 @@
+//===--- CStringMap.cpp - CString Hash table map implementation -----------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file was developed by Chris Lattner and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the CStringMap class.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/CStringMap.h"
+#include <cassert>
+using namespace llvm;
+
+CStringMapVisitor::~CStringMapVisitor() {
+}
+
+CStringMapImpl::CStringMapImpl(unsigned InitSize, unsigned itemSize) {
+ assert((InitSize & (InitSize-1)) == 0 &&
+ "Init Size must be a power of 2 or zero!");
+ NumBuckets = InitSize ? InitSize : 512;
+ ItemSize = itemSize;
+ NumItems = 0;
+
+ TheTable = new ItemBucket[NumBuckets]();
+ memset(TheTable, 0, NumBuckets*sizeof(ItemBucket));
+}
+
+
+/// HashString - Compute a hash code for the specified string.
+///
+static unsigned HashString(const char *Start, const char *End) {
+ unsigned int Result = 0;
+ // Perl hash function.
+ 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 CStringMapImpl::LookupBucketFor(const char *NameStart,
+ const char *NameEnd) {
+ unsigned HTSize = NumBuckets;
+ unsigned FullHashValue = HashString(NameStart, NameEnd);
+ unsigned BucketNo = FullHashValue & (HTSize-1);
+
+ unsigned ProbeAmt = 1;
+ while (1) {
+ ItemBucket &Bucket = TheTable[BucketNo];
+ void *BucketItem = Bucket.Item;
+ // If we found an empty bucket, this key isn't in the table yet, return it.
+ if (BucketItem == 0) {
+ Bucket.FullHashValue = FullHashValue;
+ return BucketNo;
+ }
+
+ // 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.
+ if (Bucket.FullHashValue == FullHashValue) {
+ // Do the comparison like this because NameStart isn't necessarily
+ // null-terminated!
+ char *ItemStr = (char*)BucketItem+ItemSize;
+ if (strlen(ItemStr) == unsigned(NameEnd-NameStart) &&
+ memcmp(ItemStr, NameStart, (NameEnd-NameStart)) == 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;
+ }
+}
+
+/// RehashTable - Grow the table, redistributing values into the buckets with
+/// the appropriate mod-of-hashtable-size.
+void CStringMapImpl::RehashTable() {
+ unsigned NewSize = NumBuckets*2;
+ ItemBucket *NewTableArray = new ItemBucket[NewSize]();
+ memset(NewTableArray, 0, NewSize*sizeof(ItemBucket));
+
+ // 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) {
+ // 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;
+ }
+
+ 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;
+ }
+ }
+
+ delete[] TheTable;
+
+ TheTable = NewTableArray;
+ NumBuckets = NewSize;
+}
+
+
+/// VisitEntries - This method walks through all of the items,
+/// invoking Visitor.Visit for each of them.
+void CStringMapImpl::VisitEntries(const CStringMapVisitor &Visitor) const {
+ for (ItemBucket *IB = TheTable, *E = TheTable+NumBuckets; IB != E; ++IB) {
+ if (void *Id = IB->Item)
+ Visitor.Visit((char*)Id + ItemSize, Id);
+ }
+}