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

include/llvm/ADT/CStringMap.h

@@ -0,0 +1,144 @@
+//===--- CStringMap.h - CString Hash table map interface --------*- C++ -*-===//
+//
+//                     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 defines the CStringMap class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_CSTRINGMAP_H
+#define LLVM_ADT_CSTRINGMAP_H
+
+#include "llvm/Support/Allocator.h"
+#include <cstring>
+
+namespace llvm {
+  
+/// CStringMapVisitor - Subclasses of this class may be implemented to walk all
+/// of the items in a CStringMap.
+class CStringMapVisitor {
+public:
+  virtual ~CStringMapVisitor();
+  virtual void Visit(const char *Key, void *Value) const = 0;
+};
+  
+/// CStringMapImpl - This is the base class of CStringMap that is shared among
+/// all of its instantiations.
+class CStringMapImpl {
+protected:
+  /// ItemBucket - The hash table consists of an array of these.  If Item is
+  /// non-null, this is an extant entry, otherwise, it is a hole.
+  struct ItemBucket {
+    /// FullHashValue - This remembers the full hash value of the key for
+    /// easy scanning.
+    unsigned FullHashValue;
+    
+    /// Item - This is a pointer to the actual item object.
+    void *Item;
+  };
+  
+  ItemBucket *TheTable;
+  unsigned NumBuckets;
+  unsigned NumItems;
+  unsigned ItemSize;
+protected:
+  CStringMapImpl(unsigned InitSize, unsigned ItemSize);
+  void RehashTable();
+  
+  /// 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 LookupBucketFor(const char *KeyStart, const char *KeyEnd);
+  
+public:
+  unsigned getNumBuckets() const { return NumBuckets; }
+  unsigned getNumItems() const { return NumItems; }
+
+  void VisitEntries(const CStringMapVisitor &Visitor) const;
+};
+
+
+/// CStringMap - This is an unconventional map that is specialized for handling
+/// keys that are "C strings", that is, null-terminated strings.  This does some
+/// funky memory allocation and hashing things to make it extremely efficient,
+/// storing the string data *after* the value in the map.
+template<typename ValueTy, typename AllocatorTy = MallocAllocator>
+class CStringMap : public CStringMapImpl {
+  AllocatorTy Allocator;
+public:
+  CStringMap(unsigned InitialSize = 0)
+    : CStringMapImpl(InitialSize, sizeof(ValueTy)) {}
+  
+  AllocatorTy &getAllocator() { return Allocator; }
+  const AllocatorTy &getAllocator() const { return Allocator; }
+
+  /// FindValue - Look up the specified key in the map.  If it exists, return a
+  /// pointer to the element, otherwise return null.
+  ValueTy *FindValue(const char *KeyStart, const char *KeyEnd) {
+    unsigned BucketNo = LookupBucketFor(KeyStart, KeyEnd);
+    return static_cast<ValueTy*>(TheTable[BucketNo].Item);
+  }
+  
+  /// GetOrCreateValue - Look up the specified key in the table.  If a value
+  /// exists, return it.  Otherwise, default construct a value, insert it, and
+  /// return.
+  ValueTy &GetOrCreateValue(const char *KeyStart, const char *KeyEnd) {
+    unsigned BucketNo = LookupBucketFor(KeyStart, KeyEnd);
+    ItemBucket &Bucket = TheTable[BucketNo];
+    if (Bucket.Item)
+      return *static_cast<ValueTy*>(Bucket.Item);
+    
+    unsigned KeyLength = KeyEnd-KeyStart;
+    
+    // Okay, the item doesn't already exist, and Bucket is the bucket to fill
+    // in.  Allocate a new item with space for the null-terminated string at the
+    // end.
+    unsigned AllocSize = sizeof(ValueTy)+KeyLength+1;
+    
+#ifdef __GNUC__
+    unsigned Alignment = __alignof__(ValueTy);
+#else
+    // FIXME: ugly.
+    unsigned Alignment = 8;
+#endif
+    ValueTy *NewItem = (ValueTy*)Allocator.Allocate(AllocSize, Alignment);
+    new (NewItem) ValueTy();
+    ++NumItems;
+    
+    // Copy the string information.
+    char *StrBuffer = (char*)(NewItem+1);
+    memcpy(StrBuffer, KeyStart, KeyLength);
+    StrBuffer[KeyLength] = 0;  // Null terminate string.
+    
+    // Fill in the bucket for the hash table.  The FullHashValue was already
+    // filled in by LookupBucketFor.
+    Bucket.Item = NewItem;
+    
+    // If the hash table is now more than 3/4 full, rehash into a larger table.
+    if (NumItems > NumBuckets*3/4)
+      RehashTable();
+    return *NewItem;
+  }
+  
+  ~CStringMap() {
+    for (ItemBucket *I = TheTable, *E = TheTable+NumBuckets; I != E; ++I) {
+      if (ValueTy *Id = static_cast<ValueTy*>(I->Item)) {
+        // Free memory referenced by the item.
+        Id->~ValueTy();
+        Allocator.Deallocate(Id);
+      }
+    }
+    delete [] TheTable;
+  }
+};
+  
+}
+
+#endif