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/* $OpenBSD: n_sqrt.S,v 1.3 2008/05/21 20:37:10 miod Exp $ */
/* $NetBSD: n_sqrt.S,v 1.1 1995/10/10 23:40:29 ragge Exp $ */
/*
* Copyright (c) 1985, 1993
* The Regents of the University of California. 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. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``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 REGENTS OR CONTRIBUTORS 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.
*
* @(#)sqrt.s 8.1 (Berkeley) 6/4/93
*/
#include <machine/asm.h>
#include <sys/errno.h>
/*
* double sqrt(arg) revised August 15,1982
* double arg;
* if(arg<0.0) { errno = EDOM; return(<a reserved operand>); }
* if arg is a reserved operand it is returned as it is
* W. Kahan's magic square root
* coded by Heidi Stettner and revised by Emile LeBlanc 8/18/82
*
* entry points:d_sqrt address of double arg is on the stack
* sqrt double arg is on the stack
*/
ENTRY(d_sqrt, R2|R3|R4|R5)
movq *4(ap),r0
jmp dsqrt2
ENTRY(sqrt, R2|R3|R4|R5)
movq 4(ap),r0
dsqrt2: bicw3 $0x807f,r0,r2 # check exponent of input
jeql noexp # biased exponent is zero -> 0.0 or reserved
bsbb __libm_dsqrt_r5
noexp: ret
/* **************************** internal procedure */
_ALTENTRY(__libm_dsqrt_r5) /* ENTRY POINT FOR cdabs and cdsqrt */
/* returns double square root scaled by */
/* 2^r6 */
movd r0,r4
jleq nonpos # argument is not positive
movzwl r4,r2
ashl $-1,r2,r0
addw2 $0x203c,r0 # r0 has magic initial approximation
/*
* Do two steps of Heron's rule
* ((arg/guess) + guess) / 2 = better guess
*/
divf3 r0,r4,r2
addf2 r2,r0
subw2 $0x80,r0 # divide by two
divf3 r0,r4,r2
addf2 r2,r0
subw2 $0x80,r0 # divide by two
/* Scale argument and approximation to prevent over/underflow */
bicw3 $0x807f,r4,r1
subw2 $0x4080,r1 # r1 contains scaling factor
subw2 r1,r4
movl r0,r2
subw2 r1,r2
/* Cubic step
*
* b = a + 2*a*(n-a*a)/(n+3*a*a) where b is better approximation,
* a is approximation, and n is the original argument.
* (let s be scale factor in the following comments)
*/
clrl r1
clrl r3
muld2 r0,r2 # r2:r3 = a*a/s
subd2 r2,r4 # r4:r5 = n/s - a*a/s
addw2 $0x100,r2 # r2:r3 = 4*a*a/s
addd2 r4,r2 # r2:r3 = n/s + 3*a*a/s
muld2 r0,r4 # r4:r5 = a*n/s - a*a*a/s
divd2 r2,r4 # r4:r5 = a*(n-a*a)/(n+3*a*a)
addw2 $0x80,r4 # r4:r5 = 2*a*(n-a*a)/(n+3*a*a)
addd2 r4,r0 # r0:r1 = a + 2*a*(n-a*a)/(n+3*a*a)
rsb # DONE!
nonpos:
jneq negarg
ret # argument and root are zero
negarg:
pushl $EDOM
calls $1,_C_LABEL(infnan) # generate the reserved op fault
ret
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