tan.s

<B>Digital的Unix操作系统VAX 4.2源码</B>

#ifndef lint
#static char	*sccsid = "@(#)tan.s	4.1	(ULTRIX)	7/17/90";
#endif lint

/************************************************************************
 *									*
 *			Copyright (c) 1986 by				*
 *		Digital Equipment Corporation, Maynard, MA		*
 *			All rights reserved.				*
 *									*
 *   This software is furnished under a license and may be used and	*
 *   copied  only  in accordance with the terms of such license and	*
 *   with the  inclusion  of  the  above  copyright  notice.   This	*
 *   software  or  any  other copies thereof may not be provided or	*
 *   otherwise made available to any other person.  No title to and	*
 *   ownership of the software is hereby transferred.			*
 *									*
 *   This software is  derived  from  software  received  from  the	*
 *   University    of   California,   Berkeley,   and   from   Bell	*
 *   Laboratories.  Use, duplication, or disclosure is  subject  to	*
 *   restrictions  under  license  agreements  with  University  of	*
 *   California and with AT&T.						*
 *									*
 *   The information in this software is subject to change  without	*
 *   notice  and should not be construed as a commitment by Digital	*
 *   Equipment Corporation.						*
 *									*
 *   Digital assumes no responsibility for the use  or  reliability	*
 *   of its software on equipment which is not supplied by Digital.	*
 *									*
 ************************************************************************/

/************************************************************************
*
*			Modification History
*
*	David Metsky, 12/18/86
* 001	Adapted from tan.s 1.1 (Berkeley) 8/21/85
*
*************************************************************************/

# @(#)tan.s	1.1 (Berkeley) 8/21/85

#  This is the implementation of Peter Tang's double precision  
#  tangent for the VAX using Bob Corbett's argument reduction.
#  
#  Notes:
#       under 1,024,000 random arguments testing on [0,2*pi] 
#       tan() observed maximum error = 2.15 ulps
#
# double tan(arg)
# double arg;
# method: true range reduction to [-pi/4,pi/4], P. Tang  &  B. Corbett
# S. McDonald, April 4,  1985
#
	.globl	_tan
	.text
	.align	1

_tan:	.word	0xffc		# save r2-r11
	movq	4(ap),r0
	bicw3	$0x807f,r0,r2
	beql	1f		# if x is zero or reserved operand then return x
#
# Save the PSL's IV & FU bits on the stack.
#
	movpsl	r2
	bicw3	$0xff9f,r2,-(sp)
#
#  Clear the IV & FU bits.
#
	bicpsw	$0x0060
	jsb	libm$argred
#
#  At this point,
#	   r0  contains the quadrant number, 0, 1, 2, or 3;
#	r2/r1  contains the reduced argument as a D-format number;
#  	   r3  contains a F-format extension to the reduced argument;
#
#  Save  r3/r0  so that we can call cosine after calling sine.
#
	movq	r2,-(sp)
	movq	r0,-(sp)
#
#  Call sine.  r4 = 0  implies sine.
#
	movl	$0,r4
	jsb	libm$sincos
#
#  Save  sin(x)  in  r11/r10 .
#
	movd	r0,r10
#
#  Call cosine.  r4 = 1  implies cosine.
#
	movq	(sp)+,r0
	movq	(sp)+,r2
	movl	$1,r4
	jsb	libm$sincos
	divd3	r0,r10,r0
	bispsw	(sp)+
1:	ret