Hashing.h - utilities for hashing various data types.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150890 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/Hashing.h

@@ -0,0 +1,180 @@
+//===-- llvm/ADT/Hashing.h - Utilities for hashing --------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines utilities for computing hash values for various data types.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_HASHING_H
+#define LLVM_ADT_HASHING_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/AlignOf.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/DataTypes.h"
+
+namespace llvm {
+
+/// Class to compute a hash value from multiple data fields of arbitrary
+/// types. Note that if you are hashing a single data type, such as a
+/// string, it may be cheaper to use a hash algorithm that is tailored
+/// for that specific data type.
+/// Typical Usage:
+///    GeneralHash Hash;
+///    Hash.add(someValue);
+///    Hash.add(someOtherValue);
+///    return Hash.finish();
+/// Adapted from MurmurHash2 by Austin Appleby
+class GeneralHash {
+private:
+  enum {
+    M = 0x5bd1e995
+  };
+  unsigned Hash;
+  unsigned Count;
+public:
+  GeneralHash(unsigned Seed = 0) : Hash(Seed), Count(0) {}
+
+  /// Add a pointer value.
+  /// Note: this adds pointers to the hash using sizes and endianness that
+  /// depend on the host.  It doesn't matter however, because hashing on
+  /// pointer values is inherently unstable.
+  template<typename T>
+  GeneralHash& add(const T *PtrVal) {
+    addBits(&PtrVal, &PtrVal + 1);
+    return *this;
+  }
+
+  /// Add an ArrayRef of arbitrary data.
+  template<typename T>
+  GeneralHash& add(ArrayRef<T> ArrayVal) {
+    addBits(ArrayVal.begin(), ArrayVal.end());
+    return *this;
+  }
+
+  /// Add a string
+  GeneralHash& add(StringRef StrVal) {
+    addBits(StrVal.begin(), StrVal.end());
+    return *this;
+  }
+
+  /// Add an signed 32-bit integer.
+  GeneralHash& add(int32_t Data) {
+    addInt(uint32_t(Data));
+    return *this;
+  }
+
+  /// Add an unsigned 32-bit integer.
+  GeneralHash& add(uint32_t Data) {
+    addInt(Data);
+    return *this;
+  }
+
+  /// Add an signed 64-bit integer.
+  GeneralHash& add(int64_t Data) {
+    addInt(uint64_t(Data));
+    return *this;
+  }
+
+  /// Add an unsigned 64-bit integer.
+  GeneralHash& add(uint64_t Data) {
+    addInt(Data);
+    return *this;
+  }
+
+  /// Add a float
+  GeneralHash& add(float Data) {
+    union {
+      float D; uint32_t I;
+    };
+    D = Data;
+    addInt(I);
+    return *this;
+  }
+
+  /// Add a double
+  GeneralHash& add(double Data) {
+    union {
+      double D; uint64_t I;
+    };
+    D = Data;
+    addInt(I);
+    return *this;
+  }
+
+  // Do a few final mixes of the hash to ensure the last few
+  // bytes are well-incorporated.
+  unsigned finish() {
+    mix(Count);
+    Hash ^= Hash >> 13;
+    Hash *= M;
+    Hash ^= Hash >> 15;
+    return Hash;
+  }
+
+private:
+  void mix(uint32_t Data) {
+    ++Count;
+    Data *= M;
+    Data ^= Data >> 24;
+    Data *= M;
+    Hash *= M;
+    Hash ^= Data;
+  }
+
+  // Add a single uint32 value
+  void addInt(uint32_t Val) {
+    mix(Val);
+  }
+
+  // Add a uint64 value
+  void addInt(uint64_t Val) {
+    mix(uint32_t(Val >> 32));
+    mix(uint32_t(Val));
+  }
+
+  template<typename T, bool isAligned>
+  struct addBitsImpl {
+    static void add(GeneralHash &Hash, const T *I, const T *E) {
+      Hash.addUnaligned(
+        reinterpret_cast<const uint8_t *>(I),
+        reinterpret_cast<const uint8_t *>(E));
+    }
+  };
+
+  template<typename T>
+  struct addBitsImpl<T, true> {
+    static void add(GeneralHash &Hash, const T *I, const T *E) {
+      Hash.addAligned(
+        reinterpret_cast<const uint32_t *>(I),
+        reinterpret_cast<const uint32_t *>(E));
+    }
+  };
+
+  // Add a range of bits from I to E.
+  template<typename T>
+  void addBits(const T *I, const T *E) {
+    addBitsImpl<T, AlignOf<T>::Alignment_GreaterEqual_4Bytes>::add(*this, I, E);
+  }
+
+  // Add a range of uint32s
+  void addAligned(const uint32_t *I, const uint32_t *E) {
+    while (I < E) {
+      mix(*I++);
+    }
+  }
+
+  // Add a possibly unaligned sequence of bytes.
+  void addUnaligned(const uint8_t *I, const uint8_t *E);
+};
+
+} // end namespace llvm
+
+#endif