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/* $OpenBSD: n_hypot.c,v 1.3 2009/10/27 23:59:29 deraadt Exp $ */
/* $NetBSD: n_cabs.c,v 1.1 1995/10/10 23:36:39 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.
*/
/* HYPOT(X,Y)
* RETURN THE SQUARE ROOT OF X^2 + Y^2 WHERE Z=X+iY
* DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
* CODED IN C BY K.C. NG, 11/28/84;
* REVISED BY K.C. NG, 7/12/85.
*
* Required system supported functions :
* copysign(x,y)
* finite(x)
* scalbn(x,N)
* sqrt(x)
*
* Method :
* 1. replace x by |x| and y by |y|, and swap x and
* y if y > x (hence x is never smaller than y).
* 2. Hypot(x,y) is computed by:
* Case I, x/y > 2
*
* y
* hypot = x + -----------------------------
* 2
* sqrt ( 1 + [x/y] ) + x/y
*
* Case II, x/y <= 2
* y
* hypot = x + --------------------------------------------------
* 2
* [x/y] - 2
* (sqrt(2)+1) + (x-y)/y + -----------------------------
* 2
* sqrt ( 1 + [x/y] ) + sqrt(2)
*
*
*
* Special cases:
* hypot(x,y) is INF if x or y is +INF or -INF; else
* hypot(x,y) is NAN if x or y is NAN.
*
* Accuracy:
* hypot(x,y) returns the sqrt(x^2+y^2) with error less than 1 ulps (units
* in the last place). See Kahan's "Interval Arithmetic Options in the
* Proposed IEEE Floating Point Arithmetic Standard", Interval Mathematics
* 1980, Edited by Karl L.E. Nickel, pp 99-128. (A faster but less accurate
* code follows in comments.) In a test run with 500,000 random arguments
* on a VAX, the maximum observed error was .959 ulps.
*
* Constants:
* The hexadecimal values are the intended ones for the following constants.
* The decimal values may be used, provided that the compiler will convert
* from decimal to binary accurately enough to produce the hexadecimal values
* shown.
*/
#include "math.h"
#include "mathimpl.h"
static const double r2p1hi = 2.4142135623730950345E0;
static const double r2p1lo = 1.4349369327986523769E-17;
static const double sqrt2 = 1.4142135623730950622E0;
double
hypot(double x, double y)
{
static const double zero=0, one=1,
small=1.0E-18; /* fl(1+small)==1 */
static const ibig=30; /* fl(1+2**(2*ibig))==1 */
double t,r;
int exp;
if(finite(x))
if(finite(y))
{
x=copysign(x,one);
y=copysign(y,one);
if(y > x)
{ t=x; x=y; y=t; }
if(x == zero) return(zero);
if(y == zero) return(x);
exp= logb(x);
if (exp - (int)logb(y) > ibig) {
if (one + small >= 1.0) /* raise inexact flag */
return(x); /* return |x| */
}
/* start computing sqrt(x^2 + y^2) */
r=x-y;
if(r>y) { /* x/y > 2 */
r=x/y;
r=r+sqrt(one+r*r); }
else { /* 1 <= x/y <= 2 */
r/=y; t=r*(r+2.0);
r+=t/(sqrt2+sqrt(2.0+t));
r+=r2p1lo; r+=r2p1hi; }
r=y/r;
return(x+r);
}
else if(isinf(y)) /* y is +-INF */
return(copysign(y,one));
else
return(y); /* y is NaN and x is finite */
else if(isinf(x)) /* x is +-INF */
return (copysign(x,one));
else if(finite(y))
return(x); /* x is NaN, y is finite */
else if (isnan(y))
return (y);
else return(copysign(y,one)); /* y is INF */
}
/* A faster but less accurate version of cabs(x,y) */
#if 0
double
hypot(double x, double y)
{
static const double zero=0, one=1;
small=1.0E-18; /* fl(1+small)==1 */
static const ibig=30; /* fl(1+2**(2*ibig))==1 */
double temp;
int exp;
if(finite(x))
if(finite(y))
{
x=copysign(x,one);
y=copysign(y,one);
if(y > x)
{ temp=x; x=y; y=temp; }
if(x == zero) return(zero);
if(y == zero) return(x);
exp= logb(x);
x=scalbn(x,-exp);
if (exp - (int)logb(y) > ibig) {
if (one + small >= 1.0) /* raise inexact flag */
return(scalbn(x,exp)); /* return |x| */
}
else y=scalbn(y,-exp);
return(scalbn(sqrt(x*x+y*y),exp));
}
else if(isinf(y)) /* y is +-INF */
return(copysign(y,one));
else
return(y); /* y is NaN and x is finite */
else if(isinf(x)) /* x is +-INF */
return (copysign(x,one));
else if(finite(y))
return(x); /* x is NaN, y is finite */
else if(isnan(y)) return(y); /* x and y is NaN */
else return(copysign(y,one)); /* y is INF */
}
#endif
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