python (3.12.0)
1 #ifndef Py_HASH_H
2
3 #define Py_HASH_H
4 #ifdef __cplusplus
5 extern "C" {
6 #endif
7
8 /* Helpers for hash functions */
9 #ifndef Py_LIMITED_API
10 PyAPI_FUNC(Py_hash_t) _Py_HashDouble(PyObject *, double);
11 PyAPI_FUNC(Py_hash_t) _Py_HashPointer(const void*);
12 // Similar to _Py_HashPointer(), but don't replace -1 with -2
13 PyAPI_FUNC(Py_hash_t) _Py_HashPointerRaw(const void*);
14 PyAPI_FUNC(Py_hash_t) _Py_HashBytes(const void*, Py_ssize_t);
15 #endif
16
17 /* Prime multiplier used in string and various other hashes. */
18 #define _PyHASH_MULTIPLIER 1000003UL /* 0xf4243 */
19
20 /* Parameters used for the numeric hash implementation. See notes for
21 _Py_HashDouble in Python/pyhash.c. Numeric hashes are based on
22 reduction modulo the prime 2**_PyHASH_BITS - 1. */
23
24 #if SIZEOF_VOID_P >= 8
25 # define _PyHASH_BITS 61
26 #else
27 # define _PyHASH_BITS 31
28 #endif
29
30 #define _PyHASH_MODULUS (((size_t)1 << _PyHASH_BITS) - 1)
31 #define _PyHASH_INF 314159
32 #define _PyHASH_IMAG _PyHASH_MULTIPLIER
33
34
35 /* hash secret
36 *
37 * memory layout on 64 bit systems
38 * cccccccc cccccccc cccccccc uc -- unsigned char[24]
39 * pppppppp ssssssss ........ fnv -- two Py_hash_t
40 * k0k0k0k0 k1k1k1k1 ........ siphash -- two uint64_t
41 * ........ ........ ssssssss djbx33a -- 16 bytes padding + one Py_hash_t
42 * ........ ........ eeeeeeee pyexpat XML hash salt
43 *
44 * memory layout on 32 bit systems
45 * cccccccc cccccccc cccccccc uc
46 * ppppssss ........ ........ fnv -- two Py_hash_t
47 * k0k0k0k0 k1k1k1k1 ........ siphash -- two uint64_t (*)
48 * ........ ........ ssss.... djbx33a -- 16 bytes padding + one Py_hash_t
49 * ........ ........ eeee.... pyexpat XML hash salt
50 *
51 * (*) The siphash member may not be available on 32 bit platforms without
52 * an unsigned int64 data type.
53 */
54 #ifndef Py_LIMITED_API
55 typedef union {
56 /* ensure 24 bytes */
57 unsigned char uc[24];
58 /* two Py_hash_t for FNV */
59 struct {
60 Py_hash_t prefix;
61 Py_hash_t suffix;
62 } fnv;
63 /* two uint64 for SipHash24 */
64 struct {
65 uint64_t k0;
66 uint64_t k1;
67 } siphash;
68 /* a different (!) Py_hash_t for small string optimization */
69 struct {
70 unsigned char padding[16];
71 Py_hash_t suffix;
72 } djbx33a;
73 struct {
74 unsigned char padding[16];
75 Py_hash_t hashsalt;
76 } expat;
77 } _Py_HashSecret_t;
78 PyAPI_DATA(_Py_HashSecret_t) _Py_HashSecret;
79
80 #ifdef Py_DEBUG
81 PyAPI_DATA(int) _Py_HashSecret_Initialized;
82 #endif
83
84
85 /* hash function definition */
86 typedef struct {
87 Py_hash_t (*const hash)(const void *, Py_ssize_t);
88 const char *name;
89 const int hash_bits;
90 const int seed_bits;
91 } PyHash_FuncDef;
92
93 PyAPI_FUNC(PyHash_FuncDef*) PyHash_GetFuncDef(void);
94 #endif
95
96
97 /* cutoff for small string DJBX33A optimization in range [1, cutoff).
98 *
99 * About 50% of the strings in a typical Python application are smaller than
100 * 6 to 7 chars. However DJBX33A is vulnerable to hash collision attacks.
101 * NEVER use DJBX33A for long strings!
102 *
103 * A Py_HASH_CUTOFF of 0 disables small string optimization. 32 bit platforms
104 * should use a smaller cutoff because it is easier to create colliding
105 * strings. A cutoff of 7 on 64bit platforms and 5 on 32bit platforms should
106 * provide a decent safety margin.
107 */
108 #ifndef Py_HASH_CUTOFF
109 # define Py_HASH_CUTOFF 0
110 #elif (Py_HASH_CUTOFF > 7 || Py_HASH_CUTOFF < 0)
111 # error Py_HASH_CUTOFF must in range 0...7.
112 #endif /* Py_HASH_CUTOFF */
113
114
115 /* hash algorithm selection
116 *
117 * The values for Py_HASH_* are hard-coded in the
118 * configure script.
119 *
120 * - FNV and SIPHASH* are available on all platforms and architectures.
121 * - With EXTERNAL embedders can provide an alternative implementation with::
122 *
123 * PyHash_FuncDef PyHash_Func = {...};
124 *
125 * XXX: Figure out __declspec() for extern PyHash_FuncDef.
126 */
127 #define Py_HASH_EXTERNAL 0
128 #define Py_HASH_SIPHASH24 1
129 #define Py_HASH_FNV 2
130 #define Py_HASH_SIPHASH13 3
131
132 #ifndef Py_HASH_ALGORITHM
133 # ifndef HAVE_ALIGNED_REQUIRED
134 # define Py_HASH_ALGORITHM Py_HASH_SIPHASH13
135 # else
136 # define Py_HASH_ALGORITHM Py_HASH_FNV
137 # endif /* uint64_t && uint32_t && aligned */
138 #endif /* Py_HASH_ALGORITHM */
139
140 #ifdef __cplusplus
141 }
142 #endif
143
144 #endif /* !Py_HASH_H */
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