libdpf/include/dpf/prg_lowmc.hpp

/// @file dpf/prg_lowmc.hpp
/// @brief Fixed-key LowMC PRG. Same Matyas–Meyer–Oseas stretch as `aes128`.
/// @copyright Copyright (c) 2019-2026 Ryan Henry and [others](@ref authors)
/// @license Released under a GNU General Public v2.0 (GPLv2) license;
///          see [LICENSE.md](@ref license) for details.

#ifndef LIBDPF_INCLUDE_DPF_PRG_LOWMC_HPP__
#define LIBDPF_INCLUDE_DPF_PRG_LOWMC_HPP__

#include <array>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <stdexcept>

#include "hedley/hedley.h"
#include "simde/simde/x86/avx2.h"
#include "portable-snippets/exact-int/exact-int.h"

#include "lowmc/LowMC.h"
#include "lowmc/LowMC.cpp"

namespace dpf
{

namespace prg
{

/// @brief LowMCv3, 128-bit block and key, 10 S-boxes, 32 rounds, all-zero key.
/// @details `eval(seed, pos)` is `E(seed ⊕ pos) ⊕ seed`, with `pos` in the low lane.
struct lowmc128 final
{
    using block_type = simde__m128i;

    HEDLEY_NO_THROW
    HEDLEY_ALWAYS_INLINE
    static block_type eval(block_type seed, psnip_uint32_t pos) noexcept
    {
        block_type in = simde_mm_xor_si128(seed, simde_mm_set_epi64x(0, pos));
        return simde_mm_xor_si128(permute(in), seed);
    }

    HEDLEY_NO_THROW
    HEDLEY_ALWAYS_INLINE
    static auto eval01(block_type seed) noexcept
    {
HEDLEY_PRAGMA(GCC diagnostic push)
HEDLEY_PRAGMA(GCC diagnostic ignored "-Wignored-attributes")
        return std::array<block_type, 2>{eval(seed, 0), eval(seed, 1)};
HEDLEY_PRAGMA(GCC diagnostic pop)
    }

    HEDLEY_ALWAYS_INLINE
    static void eval(block_type seed, block_type * HEDLEY_RESTRICT output,
        psnip_uint32_t count, psnip_uint32_t pos = 0)
    {
        if (count > 1 &&
            pos > static_cast<psnip_uint32_t>(~static_cast<psnip_uint32_t>(0)) - (count - 1u))
        {
            throw std::invalid_argument("prg lane index is out of range");
        }
        for (psnip_uint32_t i = 0; i < count; ++i)
        {
            output[i] = eval(seed, pos + i);
        }
    }

    HEDLEY_NO_THROW
    HEDLEY_ALWAYS_INLINE
    HEDLEY_NON_NULL(1, 2, 3)
    static void eval01_x4(const block_type * HEDLEY_RESTRICT seeds,
        block_type * HEDLEY_RESTRICT left,
        block_type * HEDLEY_RESTRICT right) noexcept
    {
        for (std::size_t i = 0; i < 4; ++i)
        {
            auto kids = eval01(seeds[i]);
            left[i] = kids[0];
            right[i] = kids[1];
        }
    }

    HEDLEY_NO_THROW
    HEDLEY_ALWAYS_INLINE
    HEDLEY_NON_NULL(1, 2)
    static void eval_x4(const block_type * HEDLEY_RESTRICT seeds,
        block_type * HEDLEY_RESTRICT output, psnip_uint32_t pos = 0) noexcept
    {
        for (std::size_t i = 0; i < 4; ++i)
        {
            output[i] = eval(seeds[i], pos);
        }
    }

    HEDLEY_NO_THROW
    HEDLEY_ALWAYS_INLINE
    HEDLEY_NON_NULL(1, 2)
    static void eval_x8(const block_type * HEDLEY_RESTRICT seeds,
        block_type * HEDLEY_RESTRICT output, psnip_uint32_t pos = 0) noexcept
    {
        for (std::size_t i = 0; i < 8; ++i)
        {
            output[i] = eval(seeds[i], pos);
        }
    }

    /// @brief Raw-bit subtractive share of `T` for party `Party` (see `prg.hpp`).
    /// @tparam T value type
    /// @tparam Party party index, `0` or `1`
    /// @param seed the PRG seed
    /// @param pos the 0-based index
    /// @return Raw-bit subtractive share of `T` for party `Party` (see `prg.hpp`)
    /// @see `prg.hpp`
    template <typename T, std::size_t Party>
    HEDLEY_NO_THROW
    static auto expand(block_type seed, psnip_uint32_t pos = 0) noexcept;

  private:
    HEDLEY_NO_THROW
    static lowmc::block to_block(block_type x) noexcept
    {
        std::uint64_t lane[2];
        std::memcpy(lane, &x, sizeof(lane));
        lowmc::block b;
        for (unsigned i = 0; i < 64; ++i)
        {
            b[i] = (lane[0] >> i) & 1ull;
            b[i + 64] = (lane[1] >> i) & 1ull;
        }
        return b;
    }

    HEDLEY_NO_THROW
    static block_type from_block(const lowmc::block & b) noexcept
    {
        std::uint64_t lane[2] = {0, 0};
        for (unsigned i = 0; i < 64; ++i)
        {
            lane[0] |= static_cast<std::uint64_t>(b[i]) << i;
            lane[1] |= static_cast<std::uint64_t>(b[i + 64]) << i;
        }
        block_type x;
        std::memcpy(&x, lane, sizeof(x));
        return x;
    }

    HEDLEY_NO_THROW
    static block_type permute(block_type x) noexcept
    {
        static lowmc::LowMC cipher;
        return from_block(cipher.encrypt(to_block(x)));
    }
};  // struct lowmc128

}  // namespace prg

}  // namespace dpf

#endif  // LIBDPF_INCLUDE_DPF_PRG_LOWMC_HPP__