GetRandomInt64 is an integer code snippet to obtain a random int64_t.
Operating system(s) or programming environment(s)
Lubuntu 13.04 (raring)
Qt Creator 2.7.0
- G++ 4.7.3
Libraries used:
STL: GNU ISO C++ Library, version
4.7.3
Qt project file: CppGetRandomInt64.pro
#ifdef _WIN32 //See http://www.richelbilderbeek.nl/CppCompileErrorSwprintfHasNotBeenDeclared.htm #undef __STRICT_ANSI__ #endif #include <cassert> #include <cinttypes> #include <cstdlib> int64_t GetRandomInt64() { static_assert(sizeof(int64_t) == 8,"int64 has 8 bytes of 8 bits each"); static_assert(RAND_MAX == 0x7FFF,"Assume RAND_MAX has 15 bits, as 0x7FFF equals 2^15"); int64_t i = 0; i += static_cast<int64_t>(std::rand()); i <<= 15; //RAND_MAX has 15 bits i += static_cast<int64_t>(std::rand()); i <<= 15; //RAND_MAX has 15 bits i += static_cast<int64_t>(std::rand()); i <<= 15; //RAND_MAX has 15 bits i += static_cast<int64_t>(std::rand()); i <<= 3; //3 bits of the 63 left, use 63 because one bit is used for the sign i += static_cast<int64_t>( (std::rand() >> 4) % (1 << 3)); assert(i >= 0); return i; } #include <cassert> #include <iostream> #include <vector> int main() { const int shift = 8; const int n_categories = (1LL << shift); //63 because one bit is used for the sign const int64_t divide_by = (1LL << (63 - shift)); std::vector<int64_t> v(n_categories,0); for (int64_t i=0; i!=(1LL << 24); ++i) { const int64_t x = GetRandomInt64(); const int index = static_cast<int>(x / divide_by); assert(index >= 0); assert(index < static_cast<int>(v.size())); ++v[index]; } for (int i=0; i!=n_categories; ++i) { std::cout << v[i] << '\t'; //All these values must be about equal } std::cout << '\n'; }