HP-UX Reference (11i v3 07/02) - 3 Library Functions N-Z (vol 7)

r
rsqrt(3M) rsqrt(3M)
(HP Integrity Server Only)
NAME
rsqrt(), rsqrtf(), rsqrtl(), rsqrtw(), rsqrtq() - reciprocal 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);
DESCRIPTION
These functions are available only for Integrity servers.
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 expres-
sions 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.
rsqrtf() is a float version of rsqrt(); it takes a float argument and returns a
float result.
Integrity Server Only
rsqrtl() is a long double version of rsqrt(); it takes a long double argument and returns
a long double result.
rsqrtw() is an extended version of rsqrt(); it takes an extended argument and returns an
extended result.
rsqrtq() is equivalent to rsqrtl() on HP-UX systems.
USAGE
To use these functions compile either with the default -Ae option or with the -Aa
and the
-D_HPUX_SOURCE options.
To use (for Integrity servers) rsqrtw() or rsqrtq(), 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.
SEE ALSO
sqrt(3M), math(5).
STANDARDS CONFORMANCE
These functions are not specified by any standard.
360 Hewlett-Packard Company − 1 − HP-UX 11i Version 3: February 2007