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The Cephes Mathematical Library author Steve Moshier has released the Cephes Mathematical Library under the BSD license. This patch patch replaces the cephes license with the BSD license for all Cephes Mathematical Library code. See also: https://bugs.gentoo.org/687276 See also: https://lists.debian.org/debian-legal/2004/12/msg00295.html See also: https://github.com/deepmind/torch-cephes/blob/master/LICENSE.txt See also: https://github.com/nearform/node-cephes/blob/master/LICENSE # Conflicts: # src/math/readme.txt
202 lines
4.2 KiB
C
202 lines
4.2 KiB
C
/* _sqrt.c
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*
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* Square root
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*
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*
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*
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* SYNOPSIS:
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*
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* double x, y, _sqrt();
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*
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* y = _sqrt( x );
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*
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*
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*
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* DESCRIPTION:
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*
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* Returns the square root of x.
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*
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* Range reduction involves isolating the power of two of the
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* argument and using a polynomial approximation to obtain
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* a rough value for the square root. Then Heron's iteration
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* is used three times to converge to an accurate value.
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*
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*
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*
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* ACCURACY:
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*
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*
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* Relative error:
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* arithmetic domain # trials peak rms
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* DEC 0, 10 60000 2.1e-17 7.9e-18
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* IEEE 0,1.7e308 30000 1.7e-16 6.3e-17
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*
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*
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* ERROR MESSAGES:
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*
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* message condition value returned
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* _sqrt domain x < 0 0.0
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*
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*/
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/*
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Cephes Math Library Release 2.8: June, 2000
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Copyright 1984, 1987, 1988, 2000 by Stephen L. Moshier
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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 are met:
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1. Redistributions of source code must retain the above copyright notice,
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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 <ORGANIZATION> nor the names of its
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contributors may be used to endorse or promote products derived from
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this software without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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AND 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 COPYRIGHT OWNER OR CONTRIBUTORS BE
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LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "mconf.h"
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#ifdef ANSIPROT
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extern double frexp ( double, int * );
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extern double ldexp ( double, int );
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#else
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double frexp(), ldexp();
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#endif
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extern double SQRT2; /* _sqrt2 = 1.41421356237309504880 */
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double c_sqrt(x)
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double x;
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{
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int e;
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#ifndef UNK
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short *q;
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#endif
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double z, w;
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if( x <= 0.0 )
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{
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if( x < 0.0 )
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mtherr( "_sqrt", DOMAIN );
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return( 0.0 );
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}
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w = x;
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/* separate exponent and significand */
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#ifdef UNK
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z = frexp( x, &e );
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#endif
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#ifdef DEC
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q = (short *)&x;
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e = ((*q >> 7) & 0377) - 0200;
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*q &= 0177;
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*q |= 040000;
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z = x;
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#endif
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/* Note, frexp and ldexp are used in order to
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* handle denormal numbers properly.
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*/
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#ifdef IBMPC
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z = frexp( x, &e );
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q = (short *)&x;
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q += 3;
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/*
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e = ((*q >> 4) & 0x0fff) - 0x3fe;
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*q &= 0x000f;
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*q |= 0x3fe0;
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z = x;
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*/
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#endif
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#ifdef MIEEE
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z = frexp( x, &e );
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q = (short *)&x;
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/*
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e = ((*q >> 4) & 0x0fff) - 0x3fe;
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*q &= 0x000f;
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*q |= 0x3fe0;
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z = x;
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*/
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#endif
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/* approximate square root of number between 0.5 and 1
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* relative error of approximation = 7.47e-3
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*/
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x = 4.173075996388649989089E-1 + 5.9016206709064458299663E-1 * z;
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/* adjust for odd powers of 2 */
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if( (e & 1) != 0 )
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x *= SQRT2;
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/* re-insert exponent */
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#ifdef UNK
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x = ldexp( x, (e >> 1) );
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#endif
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#ifdef DEC
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*q += ((e >> 1) & 0377) << 7;
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*q &= 077777;
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#endif
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#ifdef IBMPC
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x = ldexp( x, (e >> 1) );
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/*
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*q += ((e >>1) & 0x7ff) << 4;
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*q &= 077777;
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*/
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#endif
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#ifdef MIEEE
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x = ldexp( x, (e >> 1) );
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/*
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*q += ((e >>1) & 0x7ff) << 4;
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*q &= 077777;
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*/
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#endif
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/* Newton iterations: */
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#ifdef UNK
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x = 0.5*(x + w/x);
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x = 0.5*(x + w/x);
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x = 0.5*(x + w/x);
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#endif
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/* Note, assume the square root cannot be denormal,
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* so it is safe to use integer exponent operations here.
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*/
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#ifdef DEC
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x += w/x;
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*q -= 0200;
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x += w/x;
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*q -= 0200;
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x += w/x;
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*q -= 0200;
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#endif
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#ifdef IBMPC
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x += w/x;
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*q -= 0x10;
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x += w/x;
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*q -= 0x10;
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x += w/x;
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*q -= 0x10;
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#endif
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#ifdef MIEEE
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x += w/x;
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*q -= 0x10;
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x += w/x;
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*q -= 0x10;
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x += w/x;
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*q -= 0x10;
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#endif
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return(x);
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}
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