nearbyint.c revision 25c28e83beb90e7c80452a7c818c5e6f73a07dc8
/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (the "License").
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* or http://www.opensolaris.org/os/licensing.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright 2011 Nexenta Systems, Inc. All rights reserved.
*/
/*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
#if defined(ELFOBJ)
#pragma weak nearbyint = __nearbyint
#endif
/*
* nearbyint(x) returns the nearest fp integer to x in the direction
* corresponding to the current rounding direction without raising
* the inexact exception.
*
* nearbyint(x) is x unchanged if x is +/-0 or +/-inf. If x is NaN,
* nearbyint(x) is also NaN.
*/
#include "libm.h"
#include "fenv_synonyms.h"
#include <fenv.h>
double
__nearbyint(double x) {
union {
unsigned i[2];
double d;
} xx;
unsigned hx, sx, i, frac;
int rm, j;
xx.d = x;
sx = xx.i[HIWORD] & 0x80000000;
hx = xx.i[HIWORD] & ~0x80000000;
/* handle trivial cases */
if (hx >= 0x43300000) { /* x is nan, inf, or already integral */
if (hx >= 0x7ff00000) /* x is inf or nan */
#if defined(FPADD_TRAPS_INCOMPLETE_ON_NAN)
return (hx >= 0x7ff80000 ? x : x + x);
/* assumes sparc-like QNaN */
#else
return (x + x);
#endif
return (x);
} else if ((hx | xx.i[LOWORD]) == 0) /* x is zero */
return (x);
/* get the rounding mode */
rm = fegetround();
/* flip the sense of directed roundings if x is negative */
if (sx && (rm == FE_UPWARD || rm == FE_DOWNWARD))
rm = (FE_UPWARD + FE_DOWNWARD) - rm;
/* handle |x| < 1 */
if (hx < 0x3ff00000) {
if (rm == FE_UPWARD || (rm == FE_TONEAREST &&
(hx >= 0x3fe00000 && ((hx & 0xfffff) | xx.i[LOWORD]))))
xx.i[HIWORD] = sx | 0x3ff00000;
else
xx.i[HIWORD] = sx;
xx.i[LOWORD] = 0;
return (xx.d);
}
/* round x at the integer bit */
j = 0x433 - (hx >> 20);
if (j >= 32) {
i = 1 << (j - 32);
frac = ((xx.i[HIWORD] << 1) << (63 - j)) |
(xx.i[LOWORD] >> (j - 32));
if (xx.i[LOWORD] & (i - 1))
frac |= 1;
if (!frac)
return (x);
xx.i[LOWORD] = 0;
xx.i[HIWORD] &= ~(i - 1);
if ((rm == FE_UPWARD) || ((rm == FE_TONEAREST) &&
((frac > 0x80000000u) || ((frac == 0x80000000) &&
(xx.i[HIWORD] & i)))))
xx.i[HIWORD] += i;
} else {
i = 1 << j;
frac = (xx.i[LOWORD] << 1) << (31 - j);
if (!frac)
return (x);
xx.i[LOWORD] &= ~(i - 1);
if ((rm == FE_UPWARD) || ((rm == FE_TONEAREST) &&
(frac > 0x80000000u || ((frac == 0x80000000) &&
(xx.i[LOWORD] & i))))) {
xx.i[LOWORD] += i;
if (xx.i[LOWORD] == 0)
xx.i[HIWORD]++;
}
}
return (xx.d);
}