125 lines
3.9 KiB
ArmAsm
125 lines
3.9 KiB
ArmAsm
/* $NetBSD: n_sqrt.S,v 1.7 2004/05/13 20:35:40 mhitch Exp $ */
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/*
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* Copyright (c) 1985, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)sqrt.s 8.1 (Berkeley) 6/4/93
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*/
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#include <machine/asm.h>
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/*
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* double sqrt(arg) revised August 15,1982
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* double arg;
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* if(arg<0.0) { _errno = EDOM; return(<a reserved operand>); }
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* if arg is a reserved operand it is returned as it is
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* W. Kahan's magic square root
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* coded by Heidi Stettner and revised by Emile LeBlanc 8/18/82
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*
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* entry points:_d_sqrt address of double arg is on the stack
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* _sqrt double arg is on the stack
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*/
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.set EDOM,33
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ENTRY(d_sqrt, 0x003c) # save %r5,%r4,%r3,%r2
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movq *4(%ap),%r0
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jbr dsqrt2
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ENTRY(sqrt, 0x003c) # save %r5,%r4,%r3,%r2
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movq 4(%ap),%r0
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dsqrt2: bicw3 $0x807f,%r0,%r2 # check exponent of input
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jeql noexp # biased exponent is zero -> 0.0 or reserved
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bsbb __libm_dsqrt_r5_lcl+2
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noexp: ret
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/* **************************** internal procedure */
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__libm_dsqrt_r5_lcl:
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ALTENTRY(__libm_dsqrt_r5)
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nop
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nop
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/* ENTRY POINT FOR cdabs and cdsqrt */
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/* returns double square root scaled by */
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/* 2^%r6 */
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movd %r0,%r4
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jleq nonpos # argument is not positive
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movzwl %r4,%r2
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ashl $-1,%r2,%r0
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addw2 $0x203c,%r0 # %r0 has magic initial approximation
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/*
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* Do two steps of Heron's rule
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* ((arg/guess) + guess) / 2 = better guess
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*/
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divf3 %r0,%r4,%r2
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addf2 %r2,%r0
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subw2 $0x80,%r0 # divide by two
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divf3 %r0,%r4,%r2
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addf2 %r2,%r0
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subw2 $0x80,%r0 # divide by two
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/* Scale argument and approximation to prevent over/underflow */
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bicw3 $0x807f,%r4,%r1
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subw2 $0x4080,%r1 # %r1 contains scaling factor
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subw2 %r1,%r4
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movl %r0,%r2
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subw2 %r1,%r2
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/* Cubic step
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*
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* b = a + 2*a*(n-a*a)/(n+3*a*a) where b is better approximation,
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* a is approximation, and n is the original argument.
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* (let s be scale factor in the following comments)
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*/
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clrl %r1
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clrl %r3
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muld2 %r0,%r2 # %r2:%r3 = a*a/s
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subd2 %r2,%r4 # %r4:%r5 = n/s - a*a/s
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addw2 $0x100,%r2 # %r2:%r3 = 4*a*a/s
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addd2 %r4,%r2 # %r2:%r3 = n/s + 3*a*a/s
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muld2 %r0,%r4 # %r4:%r5 = a*n/s - a*a*a/s
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divd2 %r2,%r4 # %r4:%r5 = a*(n-a*a)/(n+3*a*a)
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addw2 $0x80,%r4 # %r4:%r5 = 2*a*(n-a*a)/(n+3*a*a)
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addd2 %r4,%r0 # %r0:%r1 = a + 2*a*(n-a*a)/(n+3*a*a)
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rsb # DONE!
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nonpos:
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jneq negarg
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ret # argument and root are zero
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negarg:
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pushl $EDOM
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calls $1,_C_LABEL(infnan) # generate the reserved op fault
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ret
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ENTRY(sqrtf, 0)
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cvtfd 4(%ap),-(%sp)
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calls $2,_C_LABEL(sqrt)
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cvtdf %r0,%r0
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ret
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