DragonOS/user/libs/libc/math/round.c

#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 toint = 1 / EPS;

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