Re: Slaying the HYPOTamus

This is to go with the hypot() patch I posted the other day.

As other code, such as found in adt/float.c and adt/numeric.c, simply
assumes that isnan() exists, despite it being a C99 function, I have
assumed the same.

The below code should be placed into a file called src/port/hypot.c.

Unfortunately I do not know how to drive configure and all the other
associated build magics. Could some kind soul please implemented that
portion. (Or shove me in the right direction)

#include <math.h>
#include "c.h"
#include "utils/builtins.h"

/*
* Find the hypotenuse. Firstly x and y are swapped, if required, to make
* x the larger number. The traditional formulae of x^2+y^2 is rearranged
* to bring x outside the sqrt. This allows computation of the hypotenuse
* for much larger magnitudes than otherwise normally possible.
*
* sqrt( x^2 + y^2 ) = sqrt( x^2( 1 + y^2/x^2) )
* = x * sqrt( 1 + y^2/x^2 )
* = x * sqrt( 1 + y/x * y/x )
*/
double hypot( double x, double y )
{
double yx;

if( isinf(x) || isinf(y) )
return get_float8_infinity();

if( isnan(x) || isnan(y) )
return get_float8_nan();

x = fabs(x);
y = fabs(y);
if (x < y) {
double temp = x;
x = y;
y = temp;
}
if (x == 0.0)
return 0.0;
else {
yx = y/x;
return x*sqrt(1.0+yx*yx);
}
}