87 lines
2.4 KiB
C++
87 lines
2.4 KiB
C++
/* @file random_seed.hpp */
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#include <iostream>
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#include <cstdint>
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#include <stdlib.h>
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#ifdef _BSD_SOURCE
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# include <bsd/stdlib.h>
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#else
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# include <sys/random.h>
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#endif
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namespace xo {
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namespace rng {
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/* generate a 64-bit random seed using /dev/urandom or similar source.
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* This is relatively expensive; at least cost of a system call
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* + may block if host has rebooted recently
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*
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* Require:
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* - T is null-constructible.
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*
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* return value will contain a T-instance in which representation
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* has been populated with random bits. Expecting T to be something
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* like int32_t, or std::array<uint64_t, ..>
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*/
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template<typename T>
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void random_seed(T * p_seed) {
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# ifdef __APPLE__
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/* NOTE: arc4random_buf() works on darwin/nix;
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* probably need to do something else on intel linux
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*/
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::arc4random_buf(p_seed, sizeof(*p_seed));
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# else
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/* avail flags: GRND_RANDOM | GRND_NONBLOCK */
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while (::getrandom(p_seed, sizeof(*p_seed), 0) == -1) {
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if (errno == EINTR) {
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/* interrupted by signal, try again */
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continue;
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} else {
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break;
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}
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}
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# endif
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} /*random_seed*/
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template<typename T>
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T random_seed() {
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T retval;
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random_seed(&retval);
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return retval;
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} /*random_seed*/
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/* RAII-style random-number seed
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*
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* Usage:
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*
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* Seed<xoshiro256ss> seed;
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*
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* auto eng = xoshiro256ss(seed);
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* or
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* auto rng = UnitIntervalGen<xoshiro256ss>::make(seed);
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*/
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template<typename Engine>
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struct Seed {
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using seed_type = typename Engine::seed_type;
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Seed() { random_seed(&seed_); }
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operator seed_type const & () const { return seed_; }
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seed_type seed_;
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}; /*Seed*/
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template<typename T>
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inline std::ostream &
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operator<<(std::ostream & os,
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Seed<T> const & x)
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{
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/* NOTE: if compile error here, may want caller to #include [indentlog/print/vector.hpp] */
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os << x.seed_;
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return os;
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} /*operator<<*/
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} /*namespace rng*/
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} /*namespace xo*/
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/* end random_seed.hpp */
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