fmaxf.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
* 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)
#endif
/*
* fmax(x,y) returns the larger of x and y. If just one of the
* arguments is NaN, fmax returns the other argument. If both
* arguments are NaN, fmax returns NaN (ideally, one of the
* argument NaNs).
*
* C99 does not require that fmax(-0,+0) = fmax(+0,-0) = +0, but
* ideally fmax should satisfy this.
*
* C99 makes no mention of exceptions for fmax. I suppose ideally
* either fmax never raises any exceptions or else it raises the
* invalid operation exception if and only if some argument is a
* signaling NaN. In the former case, fmax should always return
* one of its arguments. In the latter, fmax shouldn't return a
* signaling NaN, although when both arguments are signaling NaNs,
* this ideal is at odds with the stipulation that fmax should
* always return one of its arguments.
*
* Commutativity of fmax follows from the properties listed above
* except when both arguments are NaN. In that case, fmax may be
* declared commutative by fiat because there is no portable way
* to tell different NaNs apart. Ideally fmax would be truly com-
* mutative for all arguments.
*
* On SPARC V8, fmax must involve tests and branches. Ideally,
* an implementation on SPARC V9 should avoid branching, using
* conditional moves instead where necessary, and be as efficient
* as possible in its use of other resources.
*
* It appears to be impossible to attain all of the aforementioned
* ideals simultaneously. The implementation below satisfies the
* following (on SPARC):
*
* 1. fmax(x,y) returns the larger of x and y if neither x nor y
* is NaN and the non-NaN argument if just one of x or y is NaN.
* If both x and y are NaN, fmax(x,y) returns x unchanged.
* 2. fmax(-0,+0) = fmax(+0,-0) = +0.
* 3. If either argument is a signaling NaN, fmax raises the invalid
* operation exception. Otherwise, it raises no exceptions.
*/
#include "libm.h" /* for isgreaterequal macro */
float
__fmaxf(float x, float y) {
/*
* (assuming %f0 = x, %f1 = y, return value left in %f0):
*
* fcmps %fcc0,%f1,%f1
* fmovsu %fcc0,%f0,%f1
* fcmps %fcc0,%f0,%f1
* fmovsul %fcc0,%f1,%f0
* st %f0,[x]
* st %f1,[y]
* ld [x],%l0
* ld [y],%l1
* and %l0,%l1,%l2
* sethi %hi(0x80000000),%l3
* andn %l3,%l2,%l2
* andn %l0,%l2,%l0
* st %l0,[x]
* ld [x],%f0
*
* If VIS instructions are available, use this code instead:
*
* fcmps %fcc0,%f1,%f1
* fmovsu %fcc0,%f0,%f1
* fcmps %fcc0,%f0,%f1
* fmovsul %fcc0,%f1,%f0
* fands %f0,%f1,%f2
* fzeros %f3
* fnegs %f3,%f3
* fandnot2s %f3,%f2,%f2
* fandnot2s %f0,%f2,%f0
*
* If VIS 3.0 instructions are available, use this:
*
* flcmps %fcc0,%f0,%f1
* fmovslg %fcc0,%f1,%f0 ! move if %fcc0 is 1 or 2
*/
union {
unsigned i;
float f;
unsigned s;
/* if y is nan, replace it by x */
if (y != y)
y = x;
/* if x is nan, replace it by y */
if (x != x)
x = y;
/* At this point, x and y are either both numeric, or both NaN */
if (!isnan(x) && !isgreaterequal(x, y))
x = y;
/*
* clear the sign of the result if either x or y has its sign clear
*/
xx.f = x;
yy.f = y;
xx.i &= ~s;
return (xx.f);
}