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#include "ruby/missing.h"
#include <math.h>
#include <float.h>
/* This function doesn't set errno. It should on POSIX, though. */
double
nextafter(double x, double y)
{
double x1, x2, d;
int e;
if (isnan(x))
return x;
if (isnan(y))
return y;
if (x == y)
return y;
if (x == 0) {
/* the minimum "subnormal" float */
x1 = ldexp(0.5, DBL_MIN_EXP - DBL_MANT_DIG + 1);
if (x1 == 0)
x1 = DBL_MIN; /* the minimum "normal" float */
if (0 < y)
return x1;
else
return -x1;
}
if (x < 0) {
if (isinf(x))
return -DBL_MAX;
if (x == -DBL_MAX && y < 0 && isinf(y))
return y;
}
else {
if (isinf(x))
return DBL_MAX;
if (x == DBL_MAX && 0 < y && isinf(y))
return y;
}
x1 = frexp(x, &e);
if (x < y) {
d = DBL_EPSILON/2;
if (x1 == -0.5) {
x1 *= 2;
e--;
}
}
else {
d = -DBL_EPSILON/2;
if (x1 == 0.5) {
x1 *= 2;
e--;
}
}
if (e < DBL_MIN_EXP) {
d = ldexp(d, DBL_MIN_EXP-e);
}
x2 = x1 + d;
if (x2 == 0.0) {
if (x1 < 0)
return -0.0;
else
return +0.0;
}
return ldexp(x2, e);
}
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