Seeding.hpp

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#pragma once
 
#include <cstdint>
#include <functional>
#include <initializer_list>
#include <random>
#include <string_view>
 
namespace vulcan::rng {

inline uint64_t hardware_seed() {
    std::random_device rd;
    // Combine two 32-bit values for 64-bit seed
    uint64_t high = static_cast<uint64_t>(rd()) << 32;
    uint64_t low = static_cast<uint64_t>(rd());
    return high | low;
}

inline std::seed_seq create_seed_seq(std::initializer_list<uint32_t> values) {
    return std::seed_seq(values);
}

inline uint64_t seed_from_string(std::string_view name) {
    return std::hash<std::string_view>{}(name);
}

inline uint64_t stream_seed(uint64_t base_seed, uint64_t stream_index) {
    // Golden ratio constant for 64-bit
    constexpr uint64_t PHI = 0x9E3779B97F4A7C15ULL;
    // Combine using multiplication and XOR for good mixing
    return base_seed ^ (stream_index * PHI);
}

inline uint64_t advance_seed(uint64_t seed, uint64_t n) {
    // Simple linear congruential step for seed advancement
    constexpr uint64_t A = 6364136223846793005ULL;
    constexpr uint64_t C = 1442695040888963407ULL;
    for (uint64_t i = 0; i < n; ++i) {
        seed = A * seed + C;
    }
    return seed;
}
 
} // namespace vulcan::rng