source: azure_iot_hub/trunk/musl-1.1.18/src/math/round.c@ 389

#include "libm.h"

#if FLT_EVAL_METHOD==0 || FLT_EVAL_METHOD==1
#define EPS DBL_EPSILON
#elif FLT_EVAL_METHOD==2
#define EPS LDBL_EPSILON
#endif
static const double_t toint = 1/EPS;

double round(double x)
{
        union {double f; uint64_t i;} u = {x};
        int e = u.i >> 52 & 0x7ff;
        double_t y;

        if (e >= 0x3ff+52)
                return x;
        if (u.i >> 63)
                x = -x;
        if (e < 0x3ff-1) {
                /* raise inexact if x!=0 */
                FORCE_EVAL(x + toint);
                return 0*u.f;
        }
        y = x + toint - toint - x;
        if (y > 0.5)
                y = y + x - 1;
        else if (y <= -0.5)
                y = y + x + 1;
        else
                y = y + x;
        if (u.i >> 63)
                y = -y;
        return y;
}