source: azure_iot_hub/trunk/musl-1.1.18/src/math/floor.c@ 388

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

        if (e >= 0x3ff+52 || x == 0)
                return x;
        /* y = int(x) - x, where int(x) is an integer neighbor of x */
        if (u.i >> 63)
                y = x - toint + toint - x;
        else
                y = x + toint - toint - x;
        /* special case because of non-nearest rounding modes */
        if (e <= 0x3ff-1) {
                FORCE_EVAL(y);
                return u.i >> 63 ? -1 : 0;
        }
        if (y > 0)
                return x + y - 1;
        return x + y;
}