pcg.h

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// SPDX-License-Identifier: Apache-2.0
// Copyright Contributors to the OpenQMC Project.
 
 
#pragma once
 
#include "gpu.h"
 
#include <cassert>
#include <cstdint>
 
 
namespace oqmc
{
 
namespace pcg
{
 
OQMC_HOST_DEVICE constexpr std::uint32_t stateTransition(std::uint32_t state)
{
    // LCG
    return state * 747796405u + 2891336453u;
}
 
OQMC_HOST_DEVICE constexpr std::uint32_t output(std::uint32_t state)
{
    // RXS
    state ^= state >> (4 + (state >> 28));
 
    // M
    state *= 277803737u;
 
    // XS
    state ^= state >> 22;
 
    return state;
}
 
OQMC_HOST_DEVICE constexpr std::uint32_t init()
{
    return stateTransition(0);
}
 
OQMC_HOST_DEVICE constexpr std::uint32_t init(std::uint32_t seed)
{
    return init() + seed;
}
 
OQMC_HOST_DEVICE constexpr std::uint32_t hash(std::uint32_t key)
{
    key = stateTransition(key);
    return output(key);
}
 
OQMC_HOST_DEVICE constexpr std::uint32_t rng(std::uint32_t& state)
{
    state = stateTransition(state);
    return output(state);
}
 
} // namespace pcg
 
} // namespace oqmc