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/* @(#)z_pow.c 1.0 98/08/13 */
/*
FUNCTION
<<pow>>, <<powf>>---x to the power y
INDEX
pow
INDEX
powf
SYNOPSIS
#include <math.h>
double pow(double <[x]>, double <[y]>);
float pow(float <[x]>, float <[y]>);
DESCRIPTION
<<pow>> and <<powf>> calculate <[x]> raised to the exponent <[y]>.
@tex
(That is, $x^y$.)
@end tex
RETURNS
On success, <<pow>> and <<powf>> return the value calculated.
When the argument values would produce overflow, <<pow>>
returns <<HUGE_VAL>> and set <<errno>> to <<ERANGE>>. If the
argument <[x]> passed to <<pow>> or <<powf>> is a negative
noninteger, and <[y]> is also not an integer, then <<errno>>
is set to <<EDOM>>. If <[x]> and <[y]> are both 0, then
<<pow>> and <<powf>> return <<1>>.
PORTABILITY
<<pow>> is ANSI C. <<powf>> is an extension. */
#include <float.h>
#include "fdlibm.h"
#include "zmath.h"
#ifndef _DOUBLE_IS_32BITS
double pow (double x, double y)
{
double d, k, t, r = 1.0;
int n, sign, exponent_is_even_int = 0;
__uint32_t px;
GET_HIGH_WORD (px, x);
k = modf (y, &d);
if (k == 0.0)
{
/* Exponent y is an integer. */
if (modf (ldexp (y, -1), &t))
{
/* y is odd. */
exponent_is_even_int = 0;
}
else
{
/* y is even. */
exponent_is_even_int = 1;
}
}
if (x == 0.0)
{
if (y <= 0.0)
errno = EDOM;
}
else if ((t = y * log (fabs (x))) >= BIGX)
{
errno = ERANGE;
if (px & 0x80000000)
{
/* x is negative. */
if (k)
{
/* y is not an integer. */
errno = EDOM;
x = 0.0;
}
else if (exponent_is_even_int)
x = z_infinity.d;
else
x = -z_infinity.d;
}
else
{
x = z_infinity.d;
}
}
else if (t < SMALLX)
{
errno = ERANGE;
x = 0.0;
}
else
{
if ( !k && fabs(d) <= 32767 )
{
n = (int) d;
if ((sign = (n < 0)))
n = -n;
while ( n > 0 )
{
if ((unsigned int) n % 2)
r *= x;
x *= x;
n = (unsigned int) n / 2;
}
if (sign)
r = 1.0 / r;
return r;
}
else
{
if ( px & 0x80000000 )
{
/* x is negative. */
if ( k )
{
/* y is not an integer. */
errno = EDOM;
return 0.0;
}
}
x = exp (t);
if (!exponent_is_even_int)
{
if (px & 0x80000000)
{
/* y is an odd integer, and x is negative,
so the result is negative. */
GET_HIGH_WORD (px, x);
px |= 0x80000000;
SET_HIGH_WORD (x, px);
}
}
}
}
return x;
}
#endif _DOUBLE_IS_32BITS
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