/* Set of hash utility functions to help maintaining the invariant that if a==b then hash(a)==hash(b) All the utility functions (_Py_Hash*()) return "-1" to signify an error. */ #include "Python.h" #include "pycore_pyhash.h" // _Py_HashSecret_t #ifdef __APPLE__ # include <libkern/OSByteOrder.h> #elif defined(HAVE_LE64TOH) && defined(HAVE_ENDIAN_H) # include <endian.h> #elif defined(HAVE_LE64TOH) && defined(HAVE_SYS_ENDIAN_H) # include <sys/endian.h> #endif _Py_HashSecret_t _Py_HashSecret = …; #if Py_HASH_ALGORITHM == Py_HASH_EXTERNAL extern PyHash_FuncDef PyHash_Func; #else static PyHash_FuncDef PyHash_Func; #endif /* Count Py_HashBuffer() calls */ #ifdef Py_HASH_STATS #define Py_HASH_STATS_MAX … static Py_ssize_t hashstats[Py_HASH_STATS_MAX + 1] = {0}; #endif /* For numeric types, the hash of a number x is based on the reduction of x modulo the prime P = 2**_PyHASH_BITS - 1. It's designed so that hash(x) == hash(y) whenever x and y are numerically equal, even if x and y have different types. A quick summary of the hashing strategy: (1) First define the 'reduction of x modulo P' for any rational number x; this is a standard extension of the usual notion of reduction modulo P for integers. If x == p/q (written in lowest terms), the reduction is interpreted as the reduction of p times the inverse of the reduction of q, all modulo P; if q is exactly divisible by P then define the reduction to be infinity. So we've got a well-defined map reduce : { rational numbers } -> { 0, 1, 2, ..., P-1, infinity }. (2) Now for a rational number x, define hash(x) by: reduce(x) if x >= 0 -reduce(-x) if x < 0 If the result of the reduction is infinity (this is impossible for integers, floats and Decimals) then use the predefined hash value _PyHASH_INF for x >= 0, or -_PyHASH_INF for x < 0, instead. _PyHASH_INF and -_PyHASH_INF are also used for the hashes of float and Decimal infinities. NaNs hash with a pointer hash. Having distinct hash values prevents catastrophic pileups from distinct NaN instances which used to always have the same hash value but would compare unequal. A selling point for the above strategy is that it makes it possible to compute hashes of decimal and binary floating-point numbers efficiently, even if the exponent of the binary or decimal number is large. The key point is that reduce(x * y) == reduce(x) * reduce(y) (modulo _PyHASH_MODULUS) provided that {reduce(x), reduce(y)} != {0, infinity}. The reduction of a binary or decimal float is never infinity, since the denominator is a power of 2 (for binary) or a divisor of a power of 10 (for decimal). So we have, for nonnegative x, reduce(x * 2**e) == reduce(x) * reduce(2**e) % _PyHASH_MODULUS reduce(x * 10**e) == reduce(x) * reduce(10**e) % _PyHASH_MODULUS and reduce(10**e) can be computed efficiently by the usual modular exponentiation algorithm. For reduce(2**e) it's even better: since P is of the form 2**n-1, reduce(2**e) is 2**(e mod n), and multiplication by 2**(e mod n) modulo 2**n-1 just amounts to a rotation of bits. */ Py_hash_t _Py_HashDouble(PyObject *inst, double v) { … } Py_hash_t Py_HashPointer(const void *ptr) { … } Py_hash_t PyObject_GenericHash(PyObject *obj) { … } Py_hash_t Py_HashBuffer(const void *ptr, Py_ssize_t len) { … } void _PyHash_Fini(void) { … } PyHash_FuncDef * PyHash_GetFuncDef(void) { … } /* Optimized memcpy() for Windows */ #ifdef _MSC_VER # if SIZEOF_PY_UHASH_T == 4 #define PY_UHASH_CPY … # elif SIZEOF_PY_UHASH_T == 8 #define PY_UHASH_CPY … # else # error SIZEOF_PY_UHASH_T must be 4 or 8 # endif /* SIZEOF_PY_UHASH_T */ #else /* not Windows */ #define PY_UHASH_CPY(dst, src) … #endif /* _MSC_VER */ #if Py_HASH_ALGORITHM == Py_HASH_FNV /* ************************************************************************** * Modified Fowler-Noll-Vo (FNV) hash function */ static Py_hash_t fnv(const void *src, Py_ssize_t len) { const unsigned char *p = src; Py_uhash_t x; Py_ssize_t remainder, blocks; union { Py_uhash_t value; unsigned char bytes[SIZEOF_PY_UHASH_T]; } block; #ifdef Py_DEBUG assert(_Py_HashSecret_Initialized); #endif remainder = len % SIZEOF_PY_UHASH_T; if (remainder == 0) { /* Process at least one block byte by byte to reduce hash collisions * for strings with common prefixes. */ remainder = SIZEOF_PY_UHASH_T; } blocks = (len - remainder) / SIZEOF_PY_UHASH_T; x = (Py_uhash_t) _Py_HashSecret.fnv.prefix; x ^= (Py_uhash_t) *p << 7; while (blocks--) { PY_UHASH_CPY(block.bytes, p); x = (PyHASH_MULTIPLIER * x) ^ block.value; p += SIZEOF_PY_UHASH_T; } /* add remainder */ for (; remainder > 0; remainder--) x = (PyHASH_MULTIPLIER * x) ^ (Py_uhash_t) *p++; x ^= (Py_uhash_t) len; x ^= (Py_uhash_t) _Py_HashSecret.fnv.suffix; if (x == (Py_uhash_t) -1) { x = (Py_uhash_t) -2; } return x; } static PyHash_FuncDef PyHash_Func = {fnv, "fnv", 8 * SIZEOF_PY_HASH_T, 16 * SIZEOF_PY_HASH_T}; #endif /* Py_HASH_ALGORITHM == Py_HASH_FNV */ /* ************************************************************************** <MIT License> Copyright (c) 2013 Marek Majkowski <[email protected]> Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. </MIT License> Original location: https://github.com/majek/csiphash/ Solution inspired by code from: Samuel Neves (supercop/crypto_auth/siphash24/little) djb (supercop/crypto_auth/siphash24/little2) Jean-Philippe Aumasson (https://131002.net/siphash/siphash24.c) Modified for Python by Christian Heimes: - C89 / MSVC compatibility - _rotl64() on Windows - letoh64() fallback */ /* byte swap little endian to host endian * Endian conversion not only ensures that the hash function returns the same * value on all platforms. It is also required to for a good dispersion of * the hash values' least significant bits. */ #if PY_LITTLE_ENDIAN #define _le64toh(x) … #elif defined(__APPLE__) #define _le64toh … #elif defined(HAVE_LETOH64) #define _le64toh … #else #define _le64toh … #endif #ifdef _MSC_VER #define ROTATE … #else #define ROTATE(x, b) … #endif #define HALF_ROUND(a,b,c,d,s,t) … #define SINGLE_ROUND(v0,v1,v2,v3) … #define DOUBLE_ROUND(v0,v1,v2,v3) … static uint64_t siphash13(uint64_t k0, uint64_t k1, const void *src, Py_ssize_t src_sz) { … } #if Py_HASH_ALGORITHM == Py_HASH_SIPHASH24 static uint64_t siphash24(uint64_t k0, uint64_t k1, const void *src, Py_ssize_t src_sz) { uint64_t b = (uint64_t)src_sz << 56; const uint8_t *in = (const uint8_t*)src; uint64_t v0 = k0 ^ 0x736f6d6570736575ULL; uint64_t v1 = k1 ^ 0x646f72616e646f6dULL; uint64_t v2 = k0 ^ 0x6c7967656e657261ULL; uint64_t v3 = k1 ^ 0x7465646279746573ULL; uint64_t t; uint8_t *pt; while (src_sz >= 8) { uint64_t mi; memcpy(&mi, in, sizeof(mi)); mi = _le64toh(mi); in += sizeof(mi); src_sz -= sizeof(mi); v3 ^= mi; DOUBLE_ROUND(v0,v1,v2,v3); v0 ^= mi; } t = 0; pt = (uint8_t *)&t; switch (src_sz) { case 7: pt[6] = in[6]; _Py_FALLTHROUGH; case 6: pt[5] = in[5]; _Py_FALLTHROUGH; case 5: pt[4] = in[4]; _Py_FALLTHROUGH; case 4: memcpy(pt, in, sizeof(uint32_t)); break; case 3: pt[2] = in[2]; _Py_FALLTHROUGH; case 2: pt[1] = in[1]; _Py_FALLTHROUGH; case 1: pt[0] = in[0]; break; } b |= _le64toh(t); v3 ^= b; DOUBLE_ROUND(v0,v1,v2,v3); v0 ^= b; v2 ^= 0xff; DOUBLE_ROUND(v0,v1,v2,v3); DOUBLE_ROUND(v0,v1,v2,v3); /* modified */ t = (v0 ^ v1) ^ (v2 ^ v3); return t; } #endif uint64_t _Py_KeyedHash(uint64_t key, const void *src, Py_ssize_t src_sz) { … } #if Py_HASH_ALGORITHM == Py_HASH_SIPHASH13 static Py_hash_t pysiphash(const void *src, Py_ssize_t src_sz) { … } static PyHash_FuncDef PyHash_Func = …; #endif #if Py_HASH_ALGORITHM == Py_HASH_SIPHASH24 static Py_hash_t pysiphash(const void *src, Py_ssize_t src_sz) { return (Py_hash_t)siphash24( _le64toh(_Py_HashSecret.siphash.k0), _le64toh(_Py_HashSecret.siphash.k1), src, src_sz); } static PyHash_FuncDef PyHash_Func = {pysiphash, "siphash24", 64, 128}; #endif
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