Mercurial > cpython-lru_cache-weakref

annotate Include/pyhash.h @ 87690:66c1c9f32567 default tip

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Add use_weakref option to functools.lru_cache The use_weakref option makes lru_cache create weak references to the function arguments when creating the cache key, which prevents them from staying in the memory forever even after all other references to them are gone. This is a proof of concept for http://bugs.python.org/issue19859
author Radomir Dopieralski <devel@sheep.art.pl>
date Tue, 03 Dec 2013 16:02:48 +0100
parents adb471b9cba1
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
87288
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1 #ifndef Py_HASH_H
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2
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3 #define Py_HASH_H
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4 #ifdef __cplusplus
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5 extern "C" {
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6 #endif
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7
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8 /* Helpers for hash functions */
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9 #ifndef Py_LIMITED_API
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10 PyAPI_FUNC(Py_hash_t) _Py_HashDouble(double);
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11 PyAPI_FUNC(Py_hash_t) _Py_HashPointer(void*);
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12 PyAPI_FUNC(Py_hash_t) _Py_HashBytes(const void*, Py_ssize_t);
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13 #endif
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14
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15 /* Prime multiplier used in string and various other hashes. */
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16 #define _PyHASH_MULTIPLIER 1000003UL /* 0xf4243 */
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17
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18 /* Parameters used for the numeric hash implementation. See notes for
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19 _Py_HashDouble in Objects/object.c. Numeric hashes are based on
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20 reduction modulo the prime 2**_PyHASH_BITS - 1. */
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21
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22 #if SIZEOF_VOID_P >= 8
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23 # define _PyHASH_BITS 61
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24 #else
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25 # define _PyHASH_BITS 31
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26 #endif
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27
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28 #define _PyHASH_MODULUS (((size_t)1 << _PyHASH_BITS) - 1)
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29 #define _PyHASH_INF 314159
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30 #define _PyHASH_NAN 0
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31 #define _PyHASH_IMAG _PyHASH_MULTIPLIER
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32
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33
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34 /* hash secret
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35 *
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36 * memory layout on 64 bit systems
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37 * cccccccc cccccccc cccccccc uc -- unsigned char[24]
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38 * pppppppp ssssssss ........ fnv -- two Py_hash_t
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39 * k0k0k0k0 k1k1k1k1 ........ siphash -- two PY_UINT64_T
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40 * ........ ........ ssssssss djbx33a -- 16 bytes padding + one Py_hash_t
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41 * ........ ........ eeeeeeee pyexpat XML hash salt
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42 *
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43 * memory layout on 32 bit systems
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44 * cccccccc cccccccc cccccccc uc
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45 * ppppssss ........ ........ fnv -- two Py_hash_t
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46 * k0k0k0k0 k1k1k1k1 ........ siphash -- two PY_UINT64_T (*)
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47 * ........ ........ ssss.... djbx33a -- 16 bytes padding + one Py_hash_t
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48 * ........ ........ eeee.... pyexpat XML hash salt
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49 *
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50 * (*) The siphash member may not be available on 32 bit platforms without
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51 * an unsigned int64 data type.
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52 */
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53 typedef union {
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54 /* ensure 24 bytes */
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55 unsigned char uc[24];
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56 /* two Py_hash_t for FNV */
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57 struct {
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58 Py_hash_t prefix;
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59 Py_hash_t suffix;
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60 } fnv;
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61 #ifdef PY_UINT64_T
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62 /* two uint64 for SipHash24 */
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63 struct {
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64 PY_UINT64_T k0;
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65 PY_UINT64_T k1;
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66 } siphash;
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67 #endif
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68 /* a different (!) Py_hash_t for small string optimization */
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69 struct {
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70 unsigned char padding[16];
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71 Py_hash_t suffix;
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72 } djbx33a;
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73 struct {
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74 unsigned char padding[16];
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75 Py_hash_t hashsalt;
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76 } expat;
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77 } _Py_HashSecret_t;
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78 PyAPI_DATA(_Py_HashSecret_t) _Py_HashSecret;
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79
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80 #ifdef Py_DEBUG
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81 PyAPI_DATA(int) _Py_HashSecret_Initialized;
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82 #endif
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83
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84
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85 /* hash function definition */
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86 #ifndef Py_LIMITED_API
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87 typedef struct {
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88 Py_hash_t (*const hash)(const void *, Py_ssize_t);
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89 const char *name;
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90 const int hash_bits;
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91 const int seed_bits;
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92 } PyHash_FuncDef;
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93
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94 PyAPI_FUNC(PyHash_FuncDef*) PyHash_GetFuncDef(void);
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95 #endif
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96
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97
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98 /* cutoff for small string DJBX33A optimization in range [1, cutoff).
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99 *
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100 * About 50% of the strings in a typical Python application are smaller than
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101 * 6 to 7 chars. However DJBX33A is vulnerable to hash collision attacks.
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102 * NEVER use DJBX33A for long strings!
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103 *
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104 * A Py_HASH_CUTOFF of 0 disables small string optimization. 32 bit platforms
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105 * should use a smaller cutoff because it is easier to create colliding
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106 * strings. A cutoff of 7 on 64bit platforms and 5 on 32bit platforms should
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107 * provide a decent safety margin.
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108 */
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109 #ifndef Py_HASH_CUTOFF
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110 # define Py_HASH_CUTOFF 0
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111 #elif (Py_HASH_CUTOFF > 7 || Py_HASH_CUTOFF < 0)
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112 # error Py_HASH_CUTOFF must in range 0...7.
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113 #endif /* Py_HASH_CUTOFF */
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114
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115
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116 /* hash algorithm selection
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117 *
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118 * The values for Py_HASH_SIPHASH24 and Py_HASH_FNV are hard-coded in the
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119 * configure script.
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120 *
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121 * - FNV is available on all platforms and architectures.
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122 * - SIPHASH24 only works on plaforms that provide PY_UINT64_T and doesn't
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123 * require aligned memory for integers.
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124 * - With EXTERNAL embedders can provide an alternative implementation with::
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125 *
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126 * PyHash_FuncDef PyHash_Func = {...};
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127 *
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128 * XXX: Figure out __declspec() for extern PyHash_FuncDef.
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129 */
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130 #define Py_HASH_EXTERNAL 0
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131 #define Py_HASH_SIPHASH24 1
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132 #define Py_HASH_FNV 2
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133
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134 #ifndef Py_HASH_ALGORITHM
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135 # if (defined(PY_UINT64_T) && defined(PY_UINT32_T) \
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136 && !defined(HAVE_ALIGNED_REQUIRED))
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137 # define Py_HASH_ALGORITHM Py_HASH_SIPHASH24
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138 # else
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139 # define Py_HASH_ALGORITHM Py_HASH_FNV
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140 # endif /* uint64_t && uint32_t && aligned */
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141 #endif /* Py_HASH_ALGORITHM */
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142
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143 #ifdef __cplusplus
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144 }
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145 #endif
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146
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147 #endif /* !Py_HASH_H */