xref: /csrg-svn/lib/libm/common_source/floor.c (revision 34931)

/*
 * Copyright (c) 1985 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * All recipients should regard themselves as participants in an ongoing
 * research project and hence should feel obligated to report their
 * experiences (good or bad) with these elementary function codes, using
 * the sendbug(8) program, to the authors.
 */

#ifndef lint
static char sccsid[] = "@(#)floor.c	5.4 (Berkeley) 06/30/88";
#endif /* not lint */

#if defined(vax)||defined(tahoe)
#ifdef vax
#define _0x(A,B)	0x/**/A/**/B
#else	/* vax */
#define _0x(A,B)	0x/**/B/**/A
#endif	/* vax */
static long Lx[] = {_0x(0000,5c00),_0x(0000,0000)};	/* 2**55 */
#define L *(double *) Lx
#else	/* defined(vax)||defined(tahoe) */
static double L = 4503599627370496.0E0;		/* 2**52 */
#endif	/* defined(vax)||defined(tahoe) */

/*
 * floor(x) := the largest integer no larger than x;
 * ceil(x) := -floor(-x), for all real x.
 *
 * Note: Inexact will be signaled if x is not an integer, as is
 *	customary for IEEE 754.  No other signal can be emitted.
 */
double
floor(x)
double x;
{
	double y,ceil();

	if (
#if !defined(vax)&&!defined(tahoe)
		x != x ||	/* NaN */
#endif	/* !defined(vax)&&!defined(tahoe) */
		x >= L)		/* already an even integer */
		return x;
	else if (x < (double)0)
		return -ceil(-x);
	else {			/* now 0 <= x < L */
		y = L+x;		/* destructive store must be forced */
		y -= L;			/* an integer, and |x-y| < 1 */
		return x < y ? y-(double)1 : y;
	}
}

double
ceil(x)
double x;
{
	double y,floor();

	if (
#if !defined(vax)&&!defined(tahoe)
		x != x ||	/* NaN */
#endif	/* !defined(vax)&&!defined(tahoe) */
		x >= L)		/* already an even integer */
		return x;
	else if (x < (double)0)
		return -floor(-x);
	else {			/* now 0 <= x < L */
		y = L+x;		/* destructive store must be forced */
		y -= L;			/* an integer, and |x-y| < 1 */
		return x > y ? y+(double)1 : y;
	}
}

#ifndef national			/* rint() is in ./NATIONAL/support.s */
/*
 * algorithm for rint(x) in pseudo-pascal form ...
 *
 * real rint(x): real x;
 *	... delivers integer nearest x in direction of prevailing rounding
 *	... mode
 * const	L = (last consecutive integer)/2
 * 	  = 2**55; for VAX D
 * 	  = 2**52; for IEEE 754 Double
 * real	s,t;
 * begin
 * 	if x != x then return x;		... NaN
 * 	if |x| >= L then return x;		... already an integer
 * 	s := copysign(L,x);
 * 	t := x + s;				... = (x+s) rounded to integer
 * 	return t - s
 * end;
 *
 * Note: Inexact will be signaled if x is not an integer, as is
 *	customary for IEEE 754.  No other signal can be emitted.
 */
double
rint(x)
double x;
{
	double s,t,one = 1.0,copysign();
#if !defined(vax)&&!defined(tahoe)
	if (x != x)				/* NaN */
		return (x);
#endif	/* !defined(vax)&&!defined(tahoe) */
	if (copysign(x,one) >= L)		/* already an integer */
	    return (x);
	s = copysign(L,x);
	t = x + s;				/* x+s rounded to integer */
	return (t - s);
}
#endif	/* not national */