NAME
log(), logf() — natural logarithm functions
SYNOPSIS
#include <math.h>
double log(double x);
float logf(float x);
DESCRIPTION
log()
returns the natural logarithm of
x.
The value of
x
must be greater than zero.
logf()
is a
float
version of
log();
it takes a
float
argument and returns a
float
result.
To use this function, compile either with the default
-Ae
option or with the
-Aa
and
-D_HPUX_SOURCE
options.
logf()
is not specified by any standard, but it is
named in accordance with the conventions
specified in the "Future Library Directions" section of the
ANSI C standard.
To use 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.
Millicode versions of the
log()
and
logf()
functions are available.
Millicode versions of math library functions are usually
faster than their counterparts in the standard library.
To use these versions, compile your program with the
+Olibcalls
or the
+Oaggressive
optimization option.
If an error occurs, the millicode versions return the value described
in the RETURN VALUE section, but do not set
errno.
For more information, see the
HP-UX Floating-Point Guide.
RETURN VALUE
If
x
is +INFINITY,
log()
returns +INFINITY.
If
x
is zero,
log()
returns
-HUGE_VAL.
If
x
is NaN,
log()
returns NaN.
If
x
is less than zero,
log()
returns NaN and sets
errno
to [EDOM].
ERRORS
If
log()
fails,
errno
is set to the following value.
- [EDOM]
x
is less than zero.
STANDARDS CONFORMANCE
log(): SVID3, XPG4.2, ANSI C
