power.hpp

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#ifndef __DCONV_POWER_HPP__
#define __DCONV_POWER_HPP__
 
// C.
#include <cstdint>
 
namespace dconv
{
    namespace details
    {
        struct Power
        {
            uint64_t hi;
 
            uint64_t lo;
        };
 
        inline void umul128 (uint64_t a, uint64_t b, uint64_t& high, uint64_t& low) noexcept
        {
#if defined(__SIZEOF_INT128__)
            __uint128_t p = static_cast<__uint128_t> (a) * b;
 
            high = static_cast<uint64_t> (p >> 64);
            low = static_cast<uint64_t> (p);
#else
            uint64_t b_lo = static_cast<uint32_t> (b);
            uint64_t b_hi = b >> 32;
            uint64_t p0 = (a & 0xFFFFFFFF) * b_lo;
            uint64_t p1 = (a >> 32) * b_lo;
            uint64_t p2 = (a & 0xFFFFFFFF) * b_hi;
            uint64_t p3 = (a >> 32) * b_hi;
            uint64_t carry = (p0 >> 32) + (p1 & 0xFFFFFFFF) + (p2 & 0xFFFFFFFF);
 
            low = (carry << 32) | (p0 & 0xFFFFFFFF);
            high = (carry >> 32) + (p1 >> 32) + (p2 >> 32) + p3;
#endif
        }
    }
}
 
#endif