hash.h

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// Protocol Buffers - Google's data interchange format
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// Author: [email protected] (Kenton Varda)
//
// Deals with the fact that hash_map is not defined everywhere.

#ifndef GOOGLE_PROTOBUF_STUBS_HASH_H__
#define GOOGLE_PROTOBUF_STUBS_HASH_H__

#include <string.h>
#include <google/protobuf/stubs/common.h>
#include "config.h"

#if defined(HAVE_HASH_MAP) && defined(HAVE_HASH_SET)
#include HASH_MAP_H
#include HASH_SET_H
#else
#define MISSING_HASH
#include <map>
#include <set>
#endif

namespace google {
namespace protobuf {

#ifdef MISSING_HASH

// This system doesn't have hash_map or hash_set. Emulate them using map and
// set.

// Make hash<T> be the same as less<T>. Note that everywhere where custom
// hash functions are defined in the protobuf code, they are also defined such
// that they can be used as "less" functions, which is required by MSVC anyway.
template <typename Key>
struct hash {
 // Dummy, just to make derivative hash functions compile.
 int operator()(const Key& key) {
 GOOGLE_LOG(FATAL) << "Should never be called.";
 return 0;
 }

 inline bool operator()(const Key& a, const Key& b) const {
 return a < b;
 }
};

// Make sure char* is compared by value.
template <>
struct hash<const char*> {
 // Dummy, just to make derivative hash functions compile.
 int operator()(const char* key) {
 GOOGLE_LOG(FATAL) << "Should never be called.";
 return 0;
 }

 inline bool operator()(const char* a, const char* b) const {
 return strcmp(a, b) < 0;
 }
};

template <typename Key, typename Data,
 typename HashFcn = hash<Key>,
 typename EqualKey = int >
class hash_map : public std::map<Key, Data, HashFcn> {
 public:
 hash_map(int = 0) {}
};

template <typename Key,
 typename HashFcn = hash<Key>,
 typename EqualKey = int >
class hash_set : public std::set<Key, HashFcn> {
 public:
 hash_set(int = 0) {}
};

#elif defined(_MSC_VER) && !defined(_STLPORT_VERSION)

template <typename Key>
struct hash : public HASH_NAMESPACE::hash_compare<Key> {
};

// MSVC's hash_compare<const char*> hashes based on the string contents but
// compares based on the string pointer. WTF?
class CstringLess {
 public:
 inline bool operator()(const char* a, const char* b) const {
 return strcmp(a, b) < 0;
 }
};

template <>
struct hash<const char*>
 : public HASH_NAMESPACE::hash_compare<const char*, CstringLess> {
};

template <typename Key, typename Data,
 typename HashFcn = hash<Key>,
 typename EqualKey = int >
class hash_map : public HASH_NAMESPACE::hash_map<
 Key, Data, HashFcn> {
 public:
 hash_map(int = 0) {}
};

template <typename Key,
 typename HashFcn = hash<Key>,
 typename EqualKey = int >
class hash_set : public HASH_NAMESPACE::hash_set<
 Key, HashFcn> {
 public:
 hash_set(int = 0) {}
};

#else

template <typename Key>
struct hash : public HASH_NAMESPACE::hash<Key> {
};

template <typename Key>
struct hash<const Key*> {
 inline size_t operator()(const Key* key) const {
 return reinterpret_cast<size_t>(key);
 }
};

// Unlike the old SGI version, the TR1 "hash" does not special-case char*. So,
// we go ahead and provide our own implementation.
template <>
struct hash<const char*> {
 inline size_t operator()(const char* str) const {
 size_t result = 0;
 for (; *str != '\0'; str++) {
 result = 5 * result + *str;
 }
 return result;
 }
};

template <typename Key, typename Data,
 typename HashFcn = hash<Key>,
 typename EqualKey = std::equal_to<Key> >
class hash_map : public HASH_NAMESPACE::HASH_MAP_CLASS<
 Key, Data, HashFcn, EqualKey> {
 public:
 hash_map(int = 0) {}
};

template <typename Key,
 typename HashFcn = hash<Key>,
 typename EqualKey = std::equal_to<Key> >
class hash_set : public HASH_NAMESPACE::HASH_SET_CLASS<
 Key, HashFcn, EqualKey> {
 public:
 hash_set(int = 0) {}
};

#endif

template <>
struct hash<string> {
 inline size_t operator()(const string& key) const {
 return hash<const char*>()(key.c_str());
 }

 static const size_t bucket_size = 4;
 static const size_t min_buckets = 8;
 inline size_t operator()(const string& a, const string& b) const {
 return a < b;
 }
};

template <typename First, typename Second>
struct hash<pair<First, Second> > {
 inline size_t operator()(const pair<First, Second>& key) const {
 size_t first_hash = hash<First>()(key.first);
 size_t second_hash = hash<Second>()(key.second);

 // FIXME(kenton): What is the best way to compute this hash? I have
 // no idea! This seems a bit better than an XOR.
 return first_hash * ((1 << 16) - 1) + second_hash;
 }

 static const size_t bucket_size = 4;
 static const size_t min_buckets = 8;
 inline size_t operator()(const pair<First, Second>& a,
 const pair<First, Second>& b) const {
 return a < b;
 }
};

// Used by GCC/SGI STL only. (Why isn't this provided by the standard
// library? :( )
struct streq {
 inline bool operator()(const char* a, const char* b) const {
 return strcmp(a, b) == 0;
 }
};

} // namespace protobuf
} // namespace google

#endif // GOOGLE_PROTOBUF_STUBS_HASH_H__