e_acos.s

基于组件方式开发操作系统的OSKIT源代码

/*
 * Copyright (c) 1993,94 Winning Strategies, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by Winning Strategies, Inc.
 * 4. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * Written by:
 *	J.T. Conklin ([e-mail]), Winning Strategies, Inc.
 */

#include <machine/asm.h>

RCSID("$Id: e_acos.S,v 1.6 1997/03/09 14:00:26 bde Exp $")

/*
 * acos(x) = atan2(sqrt(1  - x^2, x).
 * Actually evaluate (1 - x^2) as (1 - x) * (1 + x) to avoid loss of
 * precision when |x| is nearly 1.
 */
ENTRY(__ieee754_acos)
	fldl	4(%esp)			/* x */
	fld1
	fld	%st(0)
	fsub	%st(2)			/* 1 - x */
	fxch	%st(1)
	fadd	%st(2)			/* 1 + x */
	fmulp	%st(1)			/* (1 - x) * (1 + x) */
	fsqrt
	fxch	%st(1)
	fpatan
	ret