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HP-UX 11i Version 3: February 2007

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log(), logf(), logl(), logw(), logq() — natural logarithm functions


#include <math.h>

double log(double x);

float logf(float x);

HP Integrity Server Only

long double logl(long double x);

extended logw(extended x);

quad logq(quad x);


log() returns the natural logarithm of x.

logf() is a float version of log(); it takes a float argument and returns a float result.

Integrity Server Only

logl() is a long double version of log(); it takes a long double argument and returns a long double result.

logw() is an extended version of log(); it takes an extended argument and returns an extended result.

logq() is equivalent to logl() on HP-UX systems.


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) logw() or logq(), 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.

For more information, see the HP-UX floating-point guide for HP Integrity servers at the following site: http://www.hp.com/go/fp.


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.

For special cases, the millicode versions return the value described in the RETURN VALUE section, but do not set errno.


If x is +INFINITY, log() returns +INFINITY.

If x is zero, log() returns -HUGE_VAL (equal to -INFINITY) and raises the divide-by-zero exception.

If x is less than zero, log() returns NaN and raises the invalid exception.

If x is NaN, log() returns NaN.

When it raises no other exception, whether log() raises the inexact exception is unspecified.


If x is less than zero, log() sets errno to [EDOM].

Integrity System Only

HP-UX libm functions on Integrity servers do not set errno by default. For errno setting, compile with the +Olibmerrno option.


log() : SVID3, XPG4.2, ANSI C, ISO/IEC C99 (including Annex F, ``IEC 60559 floating-point arithmetic'')

logf(), logl() : ISO/IEC C99 (including Annex F, ``IEC 60559 floating-point arithmetic'')

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