1 // Copyright 2016 The RE2 Authors. All Rights Reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 #ifndef UTIL_MIX_H_ 6 #define UTIL_MIX_H_ 7 8 #include <stddef.h> 9 #include <limits> 10 11 namespace re2 { 12 13 // Silence "truncation of constant value" warning for kMul in 32-bit mode. 14 // Since this is a header file, push and then pop to limit the scope. 15 #ifdef _MSC_VER 16 #pragma warning(push) 17 #pragma warning(disable: 4309) 18 #endif 19 20 class HashMix { 21 public: HashMix()22 HashMix() : hash_(1) {} HashMix(size_t val)23 explicit HashMix(size_t val) : hash_(val + 83) {} Mix(size_t val)24 void Mix(size_t val) { 25 static const size_t kMul = static_cast<size_t>(0xdc3eb94af8ab4c93ULL); 26 hash_ *= kMul; 27 hash_ = ((hash_ << 19) | 28 (hash_ >> (std::numeric_limits<size_t>::digits - 19))) + val; 29 } get()30 size_t get() const { return hash_; } 31 private: 32 size_t hash_; 33 }; 34 35 #ifdef _MSC_VER 36 #pragma warning(pop) 37 #endif 38 39 } // namespace re2 40 41 #endif // UTIL_MIX_H_ 42