1#include "libm.h"
2
3double nextafter(double x, double y)
4{
5	union {double f; uint64_t i;} ux={x}, uy={y};
6	uint64_t ax, ay;
7	int e;
8
9	if (isnan(x) || isnan(y))
10		return x + y;
11	if (ux.i == uy.i)
12		return y;
13	ax = ux.i & -1ULL/2;
14	ay = uy.i & -1ULL/2;
15	if (ax == 0) {
16		if (ay == 0)
17			return y;
18		ux.i = (uy.i & 1ULL<<63) | 1;
19	} else if (ax > ay || ((ux.i ^ uy.i) & 1ULL<<63))
20		ux.i--;
21	else
22		ux.i++;
23	e = ux.i >> 52 & 0x7ff;
24	/* raise overflow if ux.f is infinite and x is finite */
25	if (e == 0x7ff)
26		FORCE_EVAL(x+x);
27	/* raise underflow if ux.f is subnormal or zero */
28	if (e == 0)
29		FORCE_EVAL(x*x + ux.f*ux.f);
30	return ux.f;
31}
32