rsqrt.3m (2010 09)

r
rsqrt(3M) rsqrt(3M)
(HP Integrity Server Only)
NAME
rsqrt(), rsqrtf(), rsqrtl(), rsqrtw(), rsqrtq(), invsqrt(), invsqrtf(), invsqrtl(), invsqrtw(), invsqrtq() - recipro-
cal square root functions
SYNOPSIS
#include <math.h>
double rsqrt(double x);
float rsqrtf(float x );
long double rsqrtl(long double x );
extended rsqrtw(extended
x);
quad rsqrtq(quad x );
double invsqrt(double
x);
float invsqrtf(float
x);
long double invsqrtl(long double
x);
extended invsqrtw(extended
x);
quad invsqrtq(quad x );
DESCRIPTION
rsqrt() returns the reciprocal of the non-negative square root of x.
The expression a*
rsqrt(b) is intended as a higher performance alternative to a/
sqrt(b). The two
expressions are comparably accurate, but do not compute exactly the same value in every case. For
example, a*
rsqrt(a*a + b*b) can be just slightly greater than 1, in rare cases.
invsqrt() is equivalent to rsqrt(). It is provided in HP-UX to facilitate importing code from other
platforms.
rsqrtf() and invsqrtf() are float versions of rsqrt() and invsqrt(); they take a float
argument and returns a float result.
rsqrtl() and invsqrtl() are a long double version of rsqrt() and invsqrt(); they take a
long double argument and returns a long double result.
rsqrtw() and invsqrtw() are an extended version of rsqrt() and invsqrt(); they take an
extended argument and returns an extended result.
On HP-UX systems,
rsqrtq() is equivalent to rsqrtl(), and invsqrtq() is equivalent to
invsqrtl().
USAGE
To use these functions compile either with the default
-Ae option or with the -Aa and the
-D_HPUX_SOURCE options.
To use
rsqrtw(), rsqrtq(), invsqrtw(),orinvsqrtq(), compile also with the -fpwidetypes
option.
To use any of these functions, make sure your program includes
<math.h>, and link in the math library
by specifying -lm on the compiler or linker command line.
RETURN VALUE
If x is ±0,
rsqrt() returns ±INFINITY and raises the divide-by-zero exception.
If x is +INFINITY,
rsqrt() returns +0.
If x is NaN,
rsqrt() returns NaN.
If x is less than zero,
rsqrt() returns NaN and raises the invalid floating-point exception.
rsqrt() raises the inexact exception whenever a rounded result does not equal the mathematical result.
ERRORS
No errors are defined.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1