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* $NetBSD: sacos.sa,v 1.3 1994/10/26 07:49:27 cgd Exp $
* MOTOROLA MICROPROCESSOR & MEMORY TECHNOLOGY GROUP
* M68000 Hi-Performance Microprocessor Division
* M68040 Software Package
*
* M68040 Software Package Copyright (c) 1993, 1994 Motorola Inc.
* All rights reserved.
*
* THE SOFTWARE is provided on an "AS IS" basis and without warranty.
* To the maximum extent permitted by applicable law,
* MOTOROLA DISCLAIMS ALL WARRANTIES WHETHER EXPRESS OR IMPLIED,
* INCLUDING IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
* PARTICULAR PURPOSE and any warranty against infringement with
* regard to the SOFTWARE (INCLUDING ANY MODIFIED VERSIONS THEREOF)
* and any accompanying written materials.
*
* To the maximum extent permitted by applicable law,
* IN NO EVENT SHALL MOTOROLA BE LIABLE FOR ANY DAMAGES WHATSOEVER
* (INCLUDING WITHOUT LIMITATION, DAMAGES FOR LOSS OF BUSINESS
* PROFITS, BUSINESS INTERRUPTION, LOSS OF BUSINESS INFORMATION, OR
* OTHER PECUNIARY LOSS) ARISING OF THE USE OR INABILITY TO USE THE
* SOFTWARE. Motorola assumes no responsibility for the maintenance
* and support of the SOFTWARE.
*
* You are hereby granted a copyright license to use, modify, and
* distribute the SOFTWARE so long as this entire notice is retained
* without alteration in any modified and/or redistributed versions,
* and that such modified versions are clearly identified as such.
* No licenses are granted by implication, estoppel or otherwise
* under any patents or trademarks of Motorola, Inc.
*
* sacos.sa 3.3 12/19/90
*
* Description: The entry point sAcos computes the inverse cosine of
* an input argument; sAcosd does the same except for denormalized
* input.
*
* Input: Double-extended number X in location pointed to
* by address register a0.
*
* Output: The value arccos(X) returned in floating-point register Fp0.
*
* Accuracy and Monotonicity: The returned result is within 3 ulps in
* 64 significant bit, i.e. within 0.5001 ulp to 53 bits if the
* result is subsequently rounded to double precision. The
* result is provably monotonic in double precision.
*
* Speed: The program sCOS takes approximately 310 cycles.
*
* Algorithm:
*
* ACOS
* 1. If |X| >= 1, go to 3.
*
* 2. (|X| < 1) Calculate acos(X) by
* z := (1-X) / (1+X)
* acos(X) = 2 * atan( sqrt(z) ).
* Exit.
*
* 3. If |X| > 1, go to 5.
*
* 4. (|X| = 1) If X > 0, return 0. Otherwise, return Pi. Exit.
*
* 5. (|X| > 1) Generate an invalid operation by 0 * infinity.
* Exit.
*
SACOS IDNT 2,1 Motorola 040 Floating Point Software Package
section 8
PI DC.L $40000000,$C90FDAA2,$2168C235,$00000000
PIBY2 DC.L $3FFF0000,$C90FDAA2,$2168C235,$00000000
xref t_operr
xref t_frcinx
xref satan
xdef sacosd
sacosd:
*--ACOS(X) = PI/2 FOR DENORMALIZED X
fmove.l d1,fpcr ...load user's rounding mode/precision
FMOVE.X PIBY2,FP0
bra t_frcinx
xdef sacos
sacos:
FMOVE.X (a0),FP0 ...LOAD INPUT
move.l (a0),d0 ...pack exponent with upper 16 fraction
move.w 4(a0),d0
ANDI.L #$7FFFFFFF,D0
CMPI.L #$3FFF8000,D0
BGE.B ACOSBIG
*--THIS IS THE USUAL CASE, |X| < 1
*--ACOS(X) = 2 * ATAN( SQRT( (1-X)/(1+X) ) )
FMOVE.S #:3F800000,FP1
FADD.X FP0,FP1 ...1+X
FNEG.X FP0 ... -X
FADD.S #:3F800000,FP0 ...1-X
FDIV.X FP1,FP0 ...(1-X)/(1+X)
FSQRT.X FP0 ...SQRT((1-X)/(1+X))
fmovem.x fp0,(a0) ...overwrite input
move.l d1,-(sp) ;save original users fpcr
clr.l d1
bsr satan ...ATAN(SQRT([1-X]/[1+X]))
fMOVE.L (sp)+,fpcr ;restore users exceptions
FADD.X FP0,FP0 ...2 * ATAN( STUFF )
bra t_frcinx
ACOSBIG:
FABS.X FP0
FCMP.S #:3F800000,FP0
fbgt t_operr ;cause an operr exception
*--|X| = 1, ACOS(X) = 0 OR PI
move.l (a0),d0 ...pack exponent with upper 16 fraction
move.w 4(a0),d0
TST.L D0 ;D0 has original exponent+fraction
BGT.B ACOSP1
*--X = -1
*Returns PI and inexact exception
FMOVE.X PI,FP0
FMOVE.L d1,FPCR
FADD.S #:00800000,FP0 ;cause an inexact exception to be put
* ;into the 040 - will not trap until next
* ;fp inst.
bra t_frcinx
ACOSP1:
FMOVE.L d1,FPCR
FMOVE.S #:00000000,FP0
rts ;Facos of +1 is exact
end
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