#include "libm.h"

double nextafter(double x, double y)
{
        union {double f; uint64_t i;} ux={x}, uy={y};
        uint64_t ax, ay;
        int e;

        if (isnan(x) || isnan(y))
                return x + y;
        if (ux.i == uy.i)
                return y;
        ax = ux.i & -1ULL/2;
        ay = uy.i & -1ULL/2;
        if (ax == 0) {
                if (ay == 0)
                        return y;
                ux.i = (uy.i & 1ULL<<63) | 1;
        } else if (ax > ay || ((ux.i ^ uy.i) & 1ULL<<63))
                ux.i--;
        else
                ux.i++;
        e = ux.i >> 52 & 0x7ff;
        /* raise overflow if ux.f is infinite and x is finite */
        if (e == 0x7ff)
                FORCE_EVAL(x+x);
        /* raise underflow if ux.f is subnormal or zero */
        if (e == 0)
                FORCE_EVAL(x*x + ux.f*ux.f);
        return ux.f;
}