[llvm-commits] CVS: llvm/lib/Support/CStringMap.cpp

[Chris Lattner]

Changes in directory llvm/lib/Support:

CStringMap.cpp added (r1.1)
---
Log message:

add a highly efficient hash table that is specialized for mapping C strings
to some other type.


---
Diffs of the changes:  (+134 -0)

 CStringMap.cpp |  134 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 134 insertions(+)


Index: llvm/lib/Support/CStringMap.cpp
diff -c /dev/null llvm/lib/Support/CStringMap.cpp:1.1
*** /dev/null	Sun Oct 29 17:42:13 2006
--- llvm/lib/Support/CStringMap.cpp	Sun Oct 29 17:42:03 2006
***************
*** 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);
+   }
+ }