| 1 | #include <stdint.h>
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| 2 | #include <stdio.h>
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| 3 | #include <cmath>
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| 4 | #include <iostream>
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| 5 | #include <boost/multiprecision/cpp_bin_float.hpp>
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| 6 |
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| 7 | typedef boost::multiprecision::number<boost::multiprecision::cpp_bin_float<128, boost::multiprecision::backends::digit_base_2> > boost_quadfloat_t;
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| 8 |
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| 9 | double my_convert_to_double(const boost_quadfloat_t& x)
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| 10 | {
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| 11 | if (isnormal(x)) {
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| 12 | if (x.backend().exponent() < -1023+1) {
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| 13 | // subnormal or zero
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| 14 | if (x.backend().exponent() < -1023 - 52) {
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| 15 | return x.backend().sign() ? -0.0 : 0.0; // underflow
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| 16 | }
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| 17 | double adj = x.backend().sign() ? -DBL_MIN : DBL_MIN;
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| 18 | boost_quadfloat_t tmp = x + adj;
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| 19 | return tmp.convert_to<double>() - adj;
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| 20 | }
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| 21 | }
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| 22 | return x.convert_to<double>();
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| 23 | }
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| 24 |
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| 25 | int main(int , char** )
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| 26 | {
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| 27 | boost_quadfloat_t b = ldexp(boost_quadfloat_t(0x8000000000000bffull), -63 - 1023);
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| 28 | double d0 = b.convert_to<double>();
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| 29 | double d1 = std::nexttoward(d0, d0 < b ? DBL_MAX : -DBL_MAX);
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| 30 |
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| 31 | std::cout
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| 32 | << std::setprecision(21)
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| 33 | << b << " = b\n"
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| 34 | << d0 << " = d0 = b.convert_to<double>()\n"
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| 35 | << d1 << " = d1 = std::nexttoward(d0, ...)\n"
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| 36 | << abs(d0 - b) << " = abs(d0 - b)\n"
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| 37 | << abs(d1 - b) << " = abs(d1 - b)\n"
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| 38 | << ((abs(d1 - b) < abs(d0 - b)) ? "d0 is not the closest representable double!!!\n" : "o.k.\n")
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| 39 | ;
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| 40 |
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| 41 | d0 = my_convert_to_double(b);
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| 42 | d1 = std::nexttoward(d0, d0 < b ? DBL_MAX : -DBL_MAX);
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| 43 | std::cout
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| 44 | << d0 << " = d0 = my_convert_to_double(b)\n"
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| 45 | << d1 << " = d1 = std::nexttoward(d0, ...)\n"
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| 46 | << abs(d0 - b) << " = abs(d0 - b)\n"
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| 47 | << abs(d1 - b) << " = abs(d1 - b)\n"
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| 48 | << ((abs(d1 - b) < abs(d0 - b)) ? "d0 is not the closest representable double!!!\n" : "o.k.\n")
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| 49 | ;
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| 50 |
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| 51 | return 0;
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| 52 | }
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