HP-UX Reference (11i v1 05/09) - 3 Library Functions A-M (vol 6)

log(3M) log(3M)

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 speci-

fying

-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.