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/* $OpenBSD: dfsqrt.c,v 1.4 2000/01/11 08:18:43 mickey Exp $ */
/*
* Copyright 1996 1995 by Open Software Foundation, Inc.
* All Rights Reserved
*
* Permission to use, copy, modify, and distribute this software and
* its documentation for any purpose and without fee is hereby granted,
* provided that the above copyright notice appears in all copies and
* that both the copyright notice and this permission notice appear in
* supporting documentation.
*
* OSF DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE
* INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE.
*
* IN NO EVENT SHALL OSF BE LIABLE FOR ANY SPECIAL, INDIRECT, OR
* CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
* LOSS OF USE, DATA OR PROFITS, WHETHER IN ACTION OF CONTRACT,
* NEGLIGENCE, OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
* WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*
*/
/*
* pmk1.1
*/
/*
* (c) Copyright 1986 HEWLETT-PACKARD COMPANY
*
* To anyone who acknowledges that this file is provided "AS IS"
* without any express or implied warranty:
* permission to use, copy, modify, and distribute this file
* for any purpose is hereby granted without fee, provided that
* the above copyright notice and this notice appears in all
* copies, and that the name of Hewlett-Packard Company not be
* used in advertising or publicity pertaining to distribution
* of the software without specific, written prior permission.
* Hewlett-Packard Company makes no representations about the
* suitability of this software for any purpose.
*/
#include "../spmath/float.h"
#include "../spmath/dbl_float.h"
/*
* Double Floating-point Square Root
*/
/*ARGSUSED*/
int
dbl_fsqrt(srcptr,dstptr,status)
dbl_floating_point *srcptr, *dstptr;
unsigned int *status;
{
register unsigned int srcp1, srcp2, resultp1, resultp2;
register unsigned int newbitp1, newbitp2, sump1, sump2;
register int src_exponent;
register boolean guardbit = FALSE, even_exponent;
Dbl_copyfromptr(srcptr,srcp1,srcp2);
/*
* check source operand for NaN or infinity
*/
if ((src_exponent = Dbl_exponent(srcp1)) == DBL_INFINITY_EXPONENT) {
/*
* is signaling NaN?
*/
if (Dbl_isone_signaling(srcp1)) {
/* trap if INVALIDTRAP enabled */
if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
/* make NaN quiet */
Set_invalidflag();
Dbl_set_quiet(srcp1);
}
/*
* Return quiet NaN or positive infinity.
* Fall thru to negative test if negative infinity.
*/
if (Dbl_iszero_sign(srcp1) ||
Dbl_isnotzero_mantissa(srcp1,srcp2)) {
Dbl_copytoptr(srcp1,srcp2,dstptr);
return(NOEXCEPTION);
}
}
/*
* check for zero source operand
*/
if (Dbl_iszero_exponentmantissa(srcp1,srcp2)) {
Dbl_copytoptr(srcp1,srcp2,dstptr);
return(NOEXCEPTION);
}
/*
* check for negative source operand
*/
if (Dbl_isone_sign(srcp1)) {
/* trap if INVALIDTRAP enabled */
if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
/* make NaN quiet */
Set_invalidflag();
Dbl_makequietnan(srcp1,srcp2);
Dbl_copytoptr(srcp1,srcp2,dstptr);
return(NOEXCEPTION);
}
/*
* Generate result
*/
if (src_exponent > 0) {
even_exponent = Dbl_hidden(srcp1);
Dbl_clear_signexponent_set_hidden(srcp1);
}
else {
/* normalize operand */
Dbl_clear_signexponent(srcp1);
src_exponent++;
Dbl_normalize(srcp1,srcp2,src_exponent);
even_exponent = src_exponent & 1;
}
if (even_exponent) {
/* exponent is even */
/* Add comment here. Explain why odd exponent needs correction */
Dbl_leftshiftby1(srcp1,srcp2);
}
/*
* Add comment here. Explain following algorithm.
*
* Trust me, it works.
*
*/
Dbl_setzero(resultp1,resultp2);
Dbl_allp1(newbitp1) = 1 << (DBL_P - 32);
Dbl_setzero_mantissap2(newbitp2);
while (Dbl_isnotzero(newbitp1,newbitp2) && Dbl_isnotzero(srcp1,srcp2)) {
Dbl_addition(resultp1,resultp2,newbitp1,newbitp2,sump1,sump2);
if(Dbl_isnotgreaterthan(sump1,sump2,srcp1,srcp2)) {
Dbl_leftshiftby1(newbitp1,newbitp2);
/* update result */
Dbl_addition(resultp1,resultp2,newbitp1,newbitp2,
resultp1,resultp2);
Dbl_subtract(srcp1,srcp2,sump1,sump2,srcp1,srcp2);
Dbl_rightshiftby2(newbitp1,newbitp2);
}
else {
Dbl_rightshiftby1(newbitp1,newbitp2);
}
Dbl_leftshiftby1(srcp1,srcp2);
}
/* correct exponent for pre-shift */
if (even_exponent) {
Dbl_rightshiftby1(resultp1,resultp2);
}
/* check for inexact */
if (Dbl_isnotzero(srcp1,srcp2)) {
if (!even_exponent & Dbl_islessthan(resultp1,resultp2,srcp1,srcp2)) {
Dbl_increment(resultp1,resultp2);
}
guardbit = Dbl_lowmantissap2(resultp2);
Dbl_rightshiftby1(resultp1,resultp2);
/* now round result */
switch (Rounding_mode()) {
case ROUNDPLUS:
Dbl_increment(resultp1,resultp2);
break;
case ROUNDNEAREST:
/* stickybit is always true, so guardbit
* is enough to determine rounding */
if (guardbit) {
Dbl_increment(resultp1,resultp2);
}
break;
}
/* increment result exponent by 1 if mantissa overflowed */
if (Dbl_isone_hiddenoverflow(resultp1)) src_exponent+=2;
if (Is_inexacttrap_enabled()) {
Dbl_set_exponent(resultp1,
((src_exponent-DBL_BIAS)>>1)+DBL_BIAS);
Dbl_copytoptr(resultp1,resultp2,dstptr);
return(INEXACTEXCEPTION);
}
else Set_inexactflag();
}
else {
Dbl_rightshiftby1(resultp1,resultp2);
}
Dbl_set_exponent(resultp1,((src_exponent-DBL_BIAS)>>1)+DBL_BIAS);
Dbl_copytoptr(resultp1,resultp2,dstptr);
return(NOEXCEPTION);
}
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