/* @(#)s_rint.c 1.3 95/01/18 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

/*
 * rint(x)
 * Return x rounded to integral value according to the prevailing
 * rounding mode.
 * Method:
 *	Using floating addition.
 * Exception:
 *	Inexact flag raised if x not equal to rint(x).
 */

#include "math.h"

static const double
    TWO52[2] = {
	4.50359962737049600000e+15,  /* 0x43300000, 0x00000000 */
	-4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
};

double rint(double x) {
	int	 i0, j0, sx;
	unsigned i, i1;
	double	 w, t;
	i0 = __HI(x);
	sx = (i0 >> 31) & 1;
	i1 = __LO(x);
	j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
	if(j0 < 20) {
		if(j0 < 0) {
			if(((i0 & 0x7fffffff) | i1) == 0) return x;
			i1 |= (i0 & 0x0fffff);
			i0 &= 0xfffe0000;
			i0 |= ((i1 | -i1) >> 12) & 0x80000;
			__HI(x) = i0;
			w	= TWO52[sx] + x;
			t	= w - TWO52[sx];
			i0	= __HI(t);
			__HI(t) = (i0 & 0x7fffffff) | (sx << 31);
			return t;
		} else {
			i = (0x000fffff) >> j0;
			if(((i0 & i) | i1) == 0) return x; /* x is integral */
			i >>= 1;
			if(((i0 & i) | i1) != 0) {
				if(j0 == 19) i1 = 0x40000000;
				else
					i0 = (i0 & (~i)) | ((0x20000) >> j0);
			}
		}
	} else if(j0 > 51) {
		if(j0 == 0x400) return x + x; /* inf or NaN */
		else
			return x; /* x is integral */
	} else {
		i = ((unsigned)(0xffffffff)) >> (j0 - 20);
		if((i1 & i) == 0) return x; /* x is integral */
		i >>= 1;
		if((i1 & i) != 0) i1 = (i1 & (~i)) | ((0x40000000) >> (j0 - 20));
	}
	__HI(x) = i0;
	__LO(x) = i1;
	w	= TWO52[sx] + x;
	return w - TWO52[sx];
}