newlib-cygwin/newlib/libm/mathfp/s_pow.c

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/* @(#)z_pow.c 1.0 98/08/13 */
/*
FUNCTION
<<pow>>, <<powf>>---x to the power y
INDEX
pow
INDEX
powf
ANSI_SYNOPSIS
#include <math.h>
double pow(double <[x]>, double <[y]>);
float pow(float <[x]>, float <[y]>);
TRAD_SYNOPSIS
#include <math.h>
double pow(<[x]>, <[y]>);
double <[x]>, <[y]>;
float pow(<[x]>, <[y]>);
float <[x]>, <[y]>;
DESCRIPTION
2003-10-20 Bob Wilson <bob.wilson@acm.org> * libc/locale/locale.c: Use double quotes in code. * libc/locale/locale.tex: Likewise. * libc/libc.texinfo: Hyphenate "floating-point". * libc/machine/necv70/necv70.tex: Likewise. * libc/stdio/sprintf.c: Likewise. * libc/stdio/sscanf.c: Likewise. * libc/stdlib/atof.c: Likewise. * libc/stdlib/ldtoa.c: Fix comment typo. * libc/stdlib/div.c: Use @ifnottex instead of @ifinfo. * libc/stdlib/ldiv.c: Likewise. * libm/common/s_expm1.c: Likewise. * libm/common/s_ilogb.c: Hyphenate "floating-point". Use "nonzero". * libm/common/s_infinity: Hyphenate "double- and single-precision". * libm/common/s_nan.c: Likewise. Also correct the FUNCTION summary. * libm/common/s_nextafter.c: Fix typo. Hyphenate "double-precision" and "floating-point". * libm/common/s_scalbn.c: Correct the FUNCTION summary. * libm/math/e_pow.c: Fix comment typo. * libm/math/math.tex: Hyphenate "single-precision" and "floating-point". * libm/math/s_asinh.c: Use @ifnottex instead of @ifinfo. * libm/math/s_atan.c: Likewise. * libm/math/s_frexp.c: Likewise. Also use "nonzero". * libm/math/s_isnan.c: Hyphenate "single-precision" and "floating-point". Use "nonzero". * libm/math/s_ldexp.c: Use @ifnottex instead of @ifinfo. * libm/math/w_acos.c: Likewise. * libm/math/w_acosh.c: Likewise. * libm/math/w_asin.c: Likewise. * libm/math/w_atan2.c: Likewise. * libm/math/w_atanh.c: Likewise. * libm/math/w_cosh.c: Likewise. * libm/math/w_exp.c: Likewise. * libm/math/w_exp2.c: Likewise. Add missing @end and missing @tex version of 2^x in the description. * libm/math/w_fmod.c: Use @ifnottex instead of @ifinfo. * libm/math/w_gamma.c: Likewise. * libm/math/w_hypot.c: Likewise. * libm/math/w_j0.c: Likewise. * libm/math/w_sinh.c: Likewise. * libm/math/w_pow.c: Replace "exp1.0nt" with "exponent". * libm/mathfp/mathfp.tex: Hyphenate "single-precision" and "floating-point". * libm/mathfp/e_acosh.c: Use @ifnottex instead of @ifinfo. * libm/mathfp/e_atanh.c: Likewise. * libm/mathfp/e_hypot.c: Likewise. * libm/mathfp/er_lgamma.c: Likewise. * libm/mathfp/s_acos.c: Likewise. * libm/mathfp/s_asine.c: Likewise. * libm/mathfp/s_asinh.c: Likewise. * libm/mathfp/s_atan.c: Likewise. * libm/mathfp/s_atan2.c: Likewise. * libm/mathfp/s_atangent.c: Likewise. * libm/mathfp/s_cosh.c: Likewise. * libm/mathfp/s_exp.c: Likewise. * libm/mathfp/s_fmod.c: Likewise. * libm/mathfp/s_frexp.c: Likewise. Also use "nonzero". * libm/mathfp/s_isnan.c: Hyphenate "single-precision" and "floating-point". Use "nonzero". * libm/math/s_pow.c: Replace "exp1.0nt" with "exponent". * libm/mathfp/s_ldexp.c: Use @ifnottex instead of @ifinfo. * libm/mathfp/s_sineh.c: Likewise. * libm/mathfp/w_jn.c: Likewise.
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<<pow>> and <<powf>> calculate <[x]> raised to the exponent <[y]>.
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@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>>.
You can modify error handling for these functions using <<matherr>>.
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;
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__uint32_t px;
GET_HIGH_WORD (px, x);
k = modf (y, &d);
if (k == 0.0)
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{
/* Exponent y is an integer. */
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if (modf (ldexp (y, -1), &t))
{
/* y is odd. */
exponent_is_even_int = 0;
}
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else
{
/* y is even. */
exponent_is_even_int = 1;
}
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}
if (x == 0.0 && y <= 0.0)
{
errno = EDOM;
}
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else if ((t = y * log (fabs (x))) >= BIGX)
{
errno = ERANGE;
if (px & 0x80000000)
{
/* x is negative. */
if (k)
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{
/* y is not an integer. */
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errno = EDOM;
x = 0.0;
}
else if (exponent_is_even_int)
x = z_infinity.d;
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else
x = -z_infinity.d;
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}
else
{
x = z_infinity.d;
}
}
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else if (t < SMALLX)
{
errno = ERANGE;
x = 0.0;
}
else
{
if ( !k && fabs(d) <= 32767 )
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{
n = (int) d;
if ((sign = (n < 0)))
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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 )
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{
/* y is not an integer. */
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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);
}
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}
}
}
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return x;
}
#endif _DOUBLE_IS_32BITS