87 lines
2.4 KiB
C++
87 lines
2.4 KiB
C++
#ifndef CHAOS_SERVICE_BRANCHLESS_HPP
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#define CHAOS_SERVICE_BRANCHLESS_HPP
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#include <type_traits>
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#include <climits>
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#include <cstdint>
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namespace Chaos::Service
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{
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struct Branchless
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{
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template<typename OutUInt, typename InUInt>
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static constexpr OutUInt Msb(InUInt in) noexcept
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{
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static_assert(std::is_unsigned_v<OutUInt> &&
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std::is_unsigned_v<InUInt>);
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constexpr uint8_t shift = (sizeof(InUInt) * CHAR_BIT) - 1;
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return static_cast<OutUInt>(0) - (in >> shift);
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}
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template<typename OutUInt, typename InUInt>
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static constexpr OutUInt Lt(InUInt lhs, InUInt rhs) noexcept
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{
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static_assert(std::is_unsigned_v<OutUInt> &&
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std::is_unsigned_v<InUInt>);
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static_assert(sizeof(InUInt) <= sizeof(uint64_t));
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const uint64_t lhsEx = lhs;
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const uint64_t rhsEx = rhs;
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return Msb<OutUInt>(lhsEx ^ ((lhsEx ^ rhsEx) | ((lhsEx - rhsEx) ^ lhsEx)));
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}
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template<typename OutUInt, typename InUInt>
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static constexpr OutUInt IsZero(InUInt in) noexcept
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{
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static_assert(std::is_unsigned_v<OutUInt> &&
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std::is_unsigned_v<InUInt>);
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static_assert(sizeof(InUInt) <= sizeof(uint64_t));
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const uint64_t inEx = in;
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return Msb<OutUInt>(~inEx & (inEx - 1U));
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}
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template<typename OutUInt, typename InUInt>
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static constexpr OutUInt Eq(InUInt lhs, InUInt rhs) noexcept
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{
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static_assert(std::is_unsigned_v<OutUInt> &&
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std::is_unsigned_v<InUInt>);
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return IsZero<OutUInt, InUInt>(lhs ^ rhs);
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}
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template<typename OutUInt, typename InUInt>
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static constexpr OutUInt Ge(InUInt lhs, InUInt rhs) noexcept
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{
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static_assert(std::is_unsigned_v<OutUInt> &&
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std::is_unsigned_v<InUInt>);
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return ~Lt<OutUInt>(lhs, rhs);
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}
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template<typename OutUInt, typename InUInt>
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static constexpr OutUInt Gt(InUInt lhs, InUInt rhs) noexcept
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{
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static_assert(std::is_unsigned_v<OutUInt> &&
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std::is_unsigned_v<InUInt>);
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return Lt<OutUInt>(rhs, lhs);
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}
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template<typename UInt>
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static constexpr UInt Sel(UInt mask, UInt onTrue, UInt onFalse) noexcept
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{
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static_assert(std::is_unsigned_v<UInt>);
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return (mask & onTrue) | (~mask & onFalse);
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}
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};
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} // namespace Chaos::Service
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#endif // CHAOS_SERVICE_BRANCHLESS_HPP
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