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logb.3m (2010 09)

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logb(3M) logb(3M)
NAME
logb( ), logbf( ), logbl( ), logbw( ), logbq( ) - radix-independent exponent functions
SYNOPSIS
#include <math.h>
double logb(double x);
HP Integrity Server Only
float logbf(float x);
long double logbl(long double x);
extended logbw(extended x);
quad logbq(quad x);
DESCRIPTION
The logb() function computes the exponent of the floating point value x. Formally, the return value is
the integral part of log base r of |x| as a signed floating point value, for nonzero x, where r is the radix of
the machine’s floating-point arithmetic. The radix r is 2 on HP-UX systems.
If x is denormal, it is treated as though it were normalized, before the exponent is determined.
Integrity Server Only
logbf() is a float version of logb(); it takes a float argument and returns a float
result.
logbl() is a long double version of logb(); it takes a long double argument and returns a
long double result.
logbw() is an extended version of logb(); it takes an extended argument and returns an
extended result.
logbq() is equivalent to logbl() on HP-UX systems.
USAGE
To use these functions, compile either with the default
-Ae option or with the -Aa
and
-D_HPUX_SOURCE options.
To use (for Integrity servers)
logbw() or logbq(), compile also with -fpwidetypes.
Make sure your program includes
<math.h>. Link in the math library by specifying -lm
on the com-
piler or linker command line. For more information, see the HP-UX floating-point guide for HP Integrity
servers at the following site:
http://www.hp.com/go/fp
.
RETURN VALUE
Upon successful completion,
logb() returns the exponent of x.
If x is NaN,
logb() returns NaN.
If x is ±INFINITY,
logb() returns +INFINITY.
If x is zero,
logb() returns −HUGE_VAL (equal to −INFINITY) and raises the divide-by-zero floating-
point exception.
ERRORS
If x is zero,
logb() sets errno to [EDOM].
Integrity Server Only
HP-UX
libm functions on Integrity servers do not set errno by default. For errno setting, compile
with the +Olibmerrno option.
SEE ALSO
frexp(3M), ilogb(3M), scalb(3M), scalbn(3M), scalbln(3M), math(5).
STANDARDS CONFORMANCE
logb() : SVID3, XPG4.2, ANSI C, ISO/IEC C99 (including Annex F, ‘‘IEC 60559 floating-point arith-
metic’’)
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

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