double test

#include <stdio.h>
#include <math.h>

union dbl
{
    double val;
    unsigned long long bits;
};

double sinatan(double x)
{
    return sin(atan(x));
}

double sinatan_(double x)
{
    if (x < -1e8 || x > 1e8)
        return copysign(1., x);
    else return x/sqrt(1. + x*x);
}

int main()
{
    double x;
    //x = 0x1.fffffffffffffp1023;
    //x =   0x1.fffffffffffffp-1;
    x = 1e8.;

    printf("x = %.20e\nsinatan(x) = %.20e\nsinatan(x) = %.20e\n", x, sinatan(x), sinatan_(x));

    return 0;
}