88 lines
2.5 KiB
C++
88 lines
2.5 KiB
C++
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/// @file dpf/fixed_share.hpp
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/// @brief Fixed-point arithmetic shares: `fixed<IntBits, FracBits>`.
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#ifndef LIBDPF_INCLUDE_DPF_FIXED_SHARE_HPP__
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#define LIBDPF_INCLUDE_DPF_FIXED_SHARE_HPP__
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#include <cstddef>
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#include <cstdint>
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#include <stdexcept>
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#include <type_traits>
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#include <utility>
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#include <vector>
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#include "hedley/hedley.h"
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#include "dpf/share_vec.hpp"
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#include "dpf/trunc.hpp"
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namespace dpf
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{
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template <unsigned IntBits, unsigned FracBits>
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struct fixed
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{
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static constexpr unsigned int_bits = IntBits;
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static constexpr unsigned frac_bits = FracBits;
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static constexpr unsigned width = IntBits + FracBits;
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static_assert(width > 0 && width <= 128, "fixed width 1..128");
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using ring = std::conditional_t<(width > 64), unsigned __int128, std::uint64_t>;
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ring raw{};
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fixed() = default;
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explicit fixed(ring v) : raw(v) {}
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static fixed from_integer(ring i)
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{
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return fixed{static_cast<ring>(i << FracBits)};
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}
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static fixed mul_clear(fixed a, fixed b)
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{
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const ring prod = static_cast<ring>(a.raw * b.raw);
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return fixed{static_cast<ring>(prod >> FracBits)};
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}
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friend fixed operator+(fixed a, fixed b)
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{
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return fixed{static_cast<ring>(a.raw + b.raw)};
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}
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friend fixed operator-(fixed a, fixed b)
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{
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return fixed{static_cast<ring>(a.raw - b.raw)};
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}
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};
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template <unsigned IntBits, unsigned FracBits>
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using fixed_vec = share_vec<typename fixed<IntBits, FracBits>::ring>;
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/// @brief Fixed-point product via mul_trunc by FracBits (Beaver, both parties).
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template <unsigned IntBits, unsigned FracBits>
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HEDLEY_WARN_UNUSED_RESULT
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std::pair<fixed_vec<IntBits, FracBits>, fixed_vec<IntBits, FracBits>>
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fixed_mul_share(const fixed_vec<IntBits, FracBits> & x0,
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const fixed_vec<IntBits, FracBits> & x1,
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const fixed_vec<IntBits, FracBits> & y0,
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const fixed_vec<IntBits, FracBits> & y1)
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{
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if (x0.size() != x1.size() || x0.size() != y0.size()
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|| y0.size() != y1.size())
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throw std::invalid_argument("fixed_mul_share size");
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fixed_vec<IntBits, FracBits> z0(x0.size(), protocol::domain::a, 0);
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fixed_vec<IntBits, FracBits> z1(x0.size(), protocol::domain::a, 1);
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for (std::size_t i = 0; i < x0.size(); ++i)
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{
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// Widen so IntBits+FracBits products do not wrap before the shift.
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auto mt = trunc::mul_exact_trunc(x0[i], x1[i], y0[i], y1[i], FracBits);
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z0[i] = mt.z0;
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z1[i] = mt.z1;
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}
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return {std::move(z0), std::move(z1)};
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}
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} // namespace dpf
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#endif // LIBDPF_INCLUDE_DPF_FIXED_SHARE_HPP__
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