relibc_openlibm/src/s_logbl.c

/*
 * From: @(#)s_ilogb.c 5.1 93/09/24
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

#include <float.h>
#include <limits.h>
#include <openlibm.h>
#include "math_private.h"
#include "fpmath.h"

DLLEXPORT long double
logbl(long double x)
{
	union IEEEl2bits u;
	unsigned long m;
	int b;

	u.e = x;
	if (u.bits.exp == 0) {
		if ((u.bits.manl | u.bits.manh) == 0) {	/* x == 0 */
			u.bits.sign = 1;
			return (1.0L / u.e);
		}
		/* denormalized */
		if (u.bits.manh == 0) {
			m = 1lu << (LDBL_MANL_SIZE - 1);
			for (b = LDBL_MANH_SIZE; !(u.bits.manl & m); m >>= 1)
				b++;
		} else {
			m = 1lu << (LDBL_MANH_SIZE - 1);
			for (b = 0; !(u.bits.manh & m); m >>= 1)
				b++;
		}
#ifdef LDBL_IMPLICIT_NBIT
		b++;
#endif
		return ((long double)(LDBL_MIN_EXP - b - 1));
	}
	if (u.bits.exp < (LDBL_MAX_EXP << 1) - 1)	/* normal */
		return ((long double)(u.bits.exp - LDBL_MAX_EXP + 1));
	else						/* +/- inf or nan */
		return (x * x);
}