s_isinfl.c

glibc 库, 不仅可以学习使用库函数,还可以学习函数的具体实现,是提高功力的好资料

/*
 * Written by J.T. Conklin <[e-mail]>.
 * Change for long double by Jakub Jelinek <[e-mail]>
 * Public domain.
 */

#if defined(LIBM_SCCS) && !defined(lint)
static char rcsid[] = "$NetBSD: $";
#endif

/*
 * isinfl(x) returns 1 if x is inf, -1 if x is -inf, else 0;
 * no branching!
 */

#include "math.h"
#include "math_private.h"

int
__isinfl (long double x)
{
	int64_t hx,lx;
	GET_LDOUBLE_WORDS64(hx,lx,x);
	lx |= (hx & 0x7fffffffffffffffLL) ^ 0x7fff000000000000LL;
	lx |= -lx;
	return ~(lx >> 63) & (hx >> 62);
}
hidden_def (__isinfl)
weak_alias (__isinfl, isinfl)