internal/ceres/collections_port.h

// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2010, 2011, 2012 Google Inc. All rights reserved.
// http://code.google.com/p/ceres-solver/
//
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// modification, are permitted provided that the following conditions are met:
//
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//   this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright notice,
//   this list of conditions and the following disclaimer in the documentation
//   and/or other materials provided with the distribution.
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//   used to endorse or promote products derived from this software without
//   specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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// POSSIBILITY OF SUCH DAMAGE.
//
// Author: keir@google.com (Keir Mierle)
//
// Portable HashMap and HashSet, and a specialized overload for hashing pairs.

#ifndef CERES_INTERNAL_COLLECTIONS_PORT_H_
#define CERES_INTERNAL_COLLECTIONS_PORT_H_

#include <tr1/unordered_map>
#include <tr1/unordered_set>
#include <utility>
#include "ceres/integral_types.h"
#include "ceres/internal/port.h"

namespace ceres {
namespace internal {

template<typename K, typename V>
struct HashMap : tr1::unordered_map<K, V> {};

template<typename K>
struct HashSet : tr1::unordered_set<K> {};

#ifdef _WIN32
#define GG_LONGLONG(x) x##I64
#define GG_ULONGLONG(x) x##UI64
#else
#define GG_LONGLONG(x) x##LL
#define GG_ULONGLONG(x) x##ULL
#endif

// The hash function is due to Bob Jenkins (see
// http://burtleburtle.net/bob/hash/index.html). Each mix takes 36 instructions,
// in 18 cycles if you're lucky. On x86 architectures, this requires 45
// instructions in 27 cycles, if you're lucky.
//
// 32bit version
inline void hash_mix(uint32& a, uint32& b, uint32& c) {
  a -= b; a -= c; a ^= (c>>13);
  b -= c; b -= a; b ^= (a<<8);
  c -= a; c -= b; c ^= (b>>13);
  a -= b; a -= c; a ^= (c>>12);
  b -= c; b -= a; b ^= (a<<16);
  c -= a; c -= b; c ^= (b>>5);
  a -= b; a -= c; a ^= (c>>3);
  b -= c; b -= a; b ^= (a<<10);
  c -= a; c -= b; c ^= (b>>15);
}

// 64bit version
inline void hash_mix(uint64& a, uint64& b, uint64& c) {
  a -= b; a -= c; a ^= (c>>43);
  b -= c; b -= a; b ^= (a<<9);
  c -= a; c -= b; c ^= (b>>8);
  a -= b; a -= c; a ^= (c>>38);
  b -= c; b -= a; b ^= (a<<23);
  c -= a; c -= b; c ^= (b>>5);
  a -= b; a -= c; a ^= (c>>35);
  b -= c; b -= a; b ^= (a<<49);
  c -= a; c -= b; c ^= (b>>11);
}

inline uint32 Hash32NumWithSeed(uint32 num, uint32 c) {
  // The golden ratio; an arbitrary value.
  uint32 b = 0x9e3779b9UL;
  hash_mix(num, b, c);
  return c;
}

inline uint64 Hash64NumWithSeed(uint64 num, uint64 c) {
  // More of the golden ratio.
  uint64 b = GG_ULONGLONG(0xe08c1d668b756f82);
  hash_mix(num, b, c);
  return c;
}

}  // namespace internal
}  // namespace ceres

// Since on some platforms this is a doubly-nested namespace (std::tr1) and
// others it is not, the entire namespace line must be in a macro.
CERES_HASH_NAMESPACE_START

// The outrageously annoying specializations below are for portability reasons.
// In short, it's not possible to have two overloads of hash<pair<T1, T2>

// Hasher for STL pairs. Requires hashers for both members to be defined.
template<typename T>
struct hash<pair<T, T> > {
  size_t operator()(const pair<T, T>& p) const {
    size_t h1 = hash<T>()(p.first);
    size_t h2 = hash<T>()(p.second);
    // The decision below is at compile time
    return (sizeof(h1) <= sizeof(ceres::internal::uint32)) ?
            ceres::internal::Hash32NumWithSeed(h1, h2) :
            ceres::internal::Hash64NumWithSeed(h1, h2);
  }
  // Less than operator for MSVC.
  bool operator()(const pair<T, T>& a,
                  const pair<T, T>& b) const {
    return a < b;
  }
  static const size_t bucket_size = 4;  // These are required by MSVC
  static const size_t min_buckets = 8;  // 4 and 8 are defaults.
};

CERES_HASH_NAMESPACE_END

#endif  // CERES_INTERNAL_COLLECTIONS_PORT_H_