c3-lang/libtommath/mp_hash.c
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Hash : f12c2ab5
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Date : 2021-03-26T10:47:25
Add FNV-1a hash function This allows to compute non-cryptographic hash of mp_int which can be used as a key in a hash table.
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mp_hash.c
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#include "tommath_private.h" #ifdef MP_HASH_C /* LibTomMath, multiple-precision integer library -- Tom St Denis */ /* SPDX-License-Identifier: Unlicense */ #if defined(MP_16BIT) #define FNV_1A_INIT ((uint32_t)0x811c9dc5) #define FNV_1A_PRIME ((uint32_t)0x01000193) #else #define FNV_1A_INIT ((uint64_t)0xcbf29ce484222325ULL) #define FNV_1A_PRIME ((uint64_t)0x100000001b3ULL) #endif /* computes hash of mp_int. */ mp_err mp_hash(mp_int *a, mp_hval *hash) { int x; mp_hval hval = FNV_1A_INIT; mp_digit r, mask, shift; /* FNV-1a algorithm */ mask = ((mp_digit)1 << 8) - 1uL; shift = (mp_digit)(MP_DIGIT_BIT - 8); r = 0; for (x = a->used; x --> 0;) { mp_digit rr = a->dp[x] & mask; hval ^= (mp_hval)(a->dp[x] >> 8) | (r << shift); hval *= FNV_1A_PRIME; r = rr; } hval ^= mp_isneg(a) ? (mp_hval)1 : (mp_hval)0; *hash = hval * FNV_1A_PRIME; return MP_OKAY; } #endif