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}