mingw-w64-crt/math/powil.c

#include "cephes_mconf.h"

#ifndef _SET_ERRNO
#define _SET_ERRNO(x)
#endif

long double __powil( x, nn )
long double x;
int nn;
{
long double w, y;
long double s;
int n, e, sign, asign, lx;

if( x == 0.0L )
	{
	if( nn == 0 )
		return( 1.0L );
	else if( nn < 0 )
		return( INFINITYL );
	else
		return( 0.0L );
	}

if( nn == 0 )
	return( 1.0L );


if( x < 0.0L )
	{
	asign = -1;
	x = -x;
	}
else
	asign = 0;


if( nn < 0 )
	{
	sign = -1;
	n = -nn;
	}
else
	{
	sign = 1;
	n = nn;
	}

/* Overflow detection */

/* Calculate approximate logarithm of answer */
s = x;
s = frexpl( s, &lx );
e = (lx - 1)*n;
if( (e == 0) || (e > 64) || (e < -64) )
	{
	s = (s - 7.0710678118654752e-1L) / (s +  7.0710678118654752e-1L);
	s = (2.9142135623730950L * s - 0.5L + lx) * nn * LOGE2L;
	}
else
	{
	s = LOGE2L * e;
	}

if( s > MAXLOGL )
	{
	mtherr( "__powil", OVERFLOW );
	_SET_ERRNO(ERANGE);
	y = INFINITYL;
	goto done;
	}

if( s < MINLOGL )
	{
	mtherr( "__powil", UNDERFLOW );
	_SET_ERRNO(ERANGE);
	return(0.0L);
	}
/* Handle tiny denormal answer, but with less accuracy
 * since roundoff error in 1.0/x will be amplified.
 * The precise demarcation should be the gradual underflow threshold.
 */
if( s < (-MAXLOGL+2.0L) )
	{
	x = 1.0L/x;
	sign = -sign;
	}

/* First bit of the power */
if( n & 1 )
	y = x;
		
else
	{
	y = 1.0L;
	asign = 0;
	}

w = x;
n >>= 1;
while( n )
	{
	w = w * w;	/* arg to the 2-to-the-kth power */
	if( n & 1 )	/* if that bit is set, then include in product */
		y *= w;
	n >>= 1;
	}


done:

if( asign )
	y = -y; /* odd power of negative number */
if( sign < 0 )
	y = 1.0L/y;
return(y);
}