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Teuchos_HashUtils.hpp
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4// Teuchos: Common Tools Package
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41
42#ifndef TEUCHOS_HASHUTILS_H
43#define TEUCHOS_HASHUTILS_H
44
50
51namespace Teuchos
52{
53 using std::string;
54
66 class TEUCHOSCORE_LIB_DLL_EXPORT HashUtils
67 {
68 public:
69 /* Get the next prime in a sequence of hashtable sizes */
70 static int nextPrime(int newCapacity);
71 static int getHashCode(const unsigned char *a, size_t len);
72
73 private:
74
75 // sequence of primes generated via mathematica:
76 // Table[Prime[Round[1.5^x]], {x, 8, 36}]
77 static const int primeCount_;
78 static const int primes_[];
79 /*={101, 163, 271, 443, 733, 1187, 1907, 3061,
80 4919, 7759, 12379, 19543, 30841, 48487, 75989,
81 119089, 185971, 290347, 452027, 703657, 1093237,
82 1695781, 2627993, 4067599, 6290467, 9718019,
83 15000607, 23133937, 35650091};*/
84 };
85
86
90 template <class T> int hashCode(const T& x);
91
95 template <> inline int hashCode(const int& x)
96 {
97 return x;
98 }
99
103 template <> inline int hashCode(const unsigned& x)
104 {
106 reinterpret_cast<const unsigned char *>(&x), sizeof(unsigned));
107 }
108
112 template <> inline int hashCode(const double& x)
113 {
115 reinterpret_cast<const unsigned char *>(&x), sizeof(double));
116 }
117
121 template <> inline int hashCode(const bool& x)
122 {
123 return (int) x;
124 }
125
129 template <> inline int hashCode(const long long& x)
130 {
132 reinterpret_cast<const unsigned char *>(&x), sizeof(long long));
133 }
134
138 template <> inline int hashCode(const long& x)
139 {
141 reinterpret_cast<const unsigned char *>(&x), sizeof(long));
142 }
143
147 template <> inline int hashCode(const std::string& x)
148 {
149 /* This specialization could use the HashUtils::getHashCode as well,
150 * but they are both true hashes anyway, so leaving it !
151 * */
152 const char* str = x.c_str();
153 int len = static_cast<int>(x.length());
154 int step = len/4 + 1;
155 int base = 1;
156 int rtn = 0;
157
158 for (int i=0; i<len/2; i+=step)
159 {
160 rtn += base*(int) str[i];
161 base *= 128;
162 rtn += base*(int) str[len-i-1];
163 base *= 128;
164 }
165
166 if (rtn < 0)
167 {
168 /* Convert the largest -ve int to zero and -1 to
169 * std::numeric_limits<int>::max()
170 * */
171 size_t maxIntBeforeWrap = std::numeric_limits<int>::max();
172 maxIntBeforeWrap ++;
173 rtn += maxIntBeforeWrap;
174 }
175 return rtn;
176 }
177
178}
179#endif // TEUCHOS_HASHUTILS_H
Teuchos header file which uses auto-configuration information to include necessary C++ headers.
Utilities for generating hashcodes. This is not a true hash ! For all ints and types less than ints i...
int hashCode(const T &x)
Standard interface for getting the hash code of an object.
int hashCode(const std::string &x)
Get the hash code of a std::string.
int hashCode(const double &x)
Get the hash code of a double.
int hashCode(const long &x)
Get the hash code of a long.
static int getHashCode(const unsigned char *a, size_t len)
int hashCode(const long long &x)
Get the hash code of a long long.
int hashCode(const int &x)
Get the hash code of an int.
int hashCode(const unsigned &x)
Get the hash code of an unsigned.
int hashCode(const bool &x)
Get the hash code of a bool.
The Teuchos namespace contains all of the classes, structs and enums used by Teuchos,...