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

#include "libm.h"

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

float roundf(float x)
{
        union {float f; uint32_t i;} u = {x};
        int e = u.i >> 23 & 0xff;
        float_t y;

        if (e >= 0x7f+23)
                return x;
        if (u.i >> 31)
                x = -x;
        if (e < 0x7f-1) {
                FORCE_EVAL(x + toint);
                return 0*u.f;
        }
        y = x + toint - toint - x;
        if (y > 0.5f)
                y = y + x - 1;
        else if (y <= -0.5f)
                y = y + x + 1;
        else
                y = y + x;
        if (u.i >> 31)
                y = -y;
        return y;
}