STD：：MODf

double modf(double x, double* iptr)
{
#pragma STDC FENV_ACCESS ON
    int save_round = std::fegetround(
    std::fesetround(FE_TOWARDZERO
    *iptr = std::nearbyint(x
    std::fesetround(save_round
    return std::copysign(std::isinf(x) ? 0.0 : x - (*iptr), x
}

#include <iostream>
#include <cmath>
#include <limits>
 
int main()
{
    double f = 123.45;
    std::cout << "Given the number " << f << " or " << std::hexfloat
              << f << std::defaultfloat << " in hex,\n";
 
    double f3;
    double f2 = std::modf(f, &f3
    std::cout << "modf() makes " << f3 << " + " << f2 << '\n';
 
    int i;
    f2 = std::frexp(f, &i
    std::cout << "frexp() makes " << f2 << " * 2^" << i << '\n';
 
    i = std::ilogb(f
    std::cout << "logb()/ilogb() make " << f/std::scalbn(1.0, i) << " * "
              << std::numeric_limits<double>::radix
              << "^" << std::ilogb(f) << '\n';
 
    // special values
    f2 = std::modf(-0.0, &f3
    std::cout << "modf(-0) makes " << f3 << " + " << f2 << '\n';
    f2 = std::modf(-INFINITY, &f3
    std::cout << "modf(-Inf) makes " << f3 << " + " << f2 << '\n';
 
}

Given the number 123.45 or 0x1.edccccccccccdp+6 in hex,
modf() makes 123 + 0.45
frexp() makes 0.964453 * 2^7
logb()/ilogb() make 1.92891 * 2^6
modf(-0) makes -0 + -0
modf(-Inf) makes -INF + -0

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