LOG(3M) Mathematical Library Functions LOG(3M)
log, logf, logl - natural logarithm function
c99 [ flag... ] file... -lm [ library... ]
#include <math.h>
double log(double x);
float logf(float x);
long double logl(long double x);
These functions compute the natural logarithm of their argument x,
log(e)(x).
Upon successful completion, log() returns the natural logarithm of x.
If x is +-0, a pole error occurs and log(), logf(), and logl() return
-HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respectively.
For finite values of x that are less than 0, or if x is -Inf, a
domain error occurs and a NaN is returned.
If x is NaN, a NaN is returned.
If x is 1, +0 is returned.
If x is +Inf, x is returned.
For exceptional cases, matherr(3M) tabulates the values to be
returned by log() as specified by SVID3 and XPG3.
These functions will fail if:
Domain Error
The finite value of x is negative, or x is -Inf.
If the integer expression (math_errhandling &
MATH_ERREXCEPT) is non-zero, the invalid floating-
point exception is raised.
The log() function sets errno to EDOM if the value of
x is negative.
Pole Error
The value of x is 0.
If the integer expression (math_errhandling &
MATH_ERREXCEPT) is non-zero, the divide-by-zero
floating-point exception is raised.
An application wanting to check for exceptions should call
feclearexcept(FE_ALL_EXCEPT) before calling these functions. On
return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW |
FE_UNDERFLOW) is non-zero, an exception has been raised. An
application should either examine the return value or check the
floating point exception flags to detect exceptions.
An application can also set errno to 0 before calling log(). On
return, if errno is non-zero, an error has occurred. The logf() and
logl() functions do not set errno.
See attributes(7) for descriptions of the following attributes:
+----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+----------------------------+-----------------------------+
|Interface Stability | Standard |
+----------------------------+-----------------------------+
|MT-Level | MT-Safe |
+----------------------------+-----------------------------+
math.h(3HEAD), exp(3M), feclearexcept(3M), fetestexcept(3M),
isnan(3M), log10(3M), log1p(3M), matherr(3M), attributes(7),
standards(7)
SunOS 5.11 July 12, 2006 LOG(3M)
NAME
log, logf, logl - natural logarithm function
SYNOPSIS
c99 [ flag... ] file... -lm [ library... ]
#include <math.h>
double log(double x);
float logf(float x);
long double logl(long double x);
DESCRIPTION
These functions compute the natural logarithm of their argument x,
log(e)(x).
RETURN VALUES
Upon successful completion, log() returns the natural logarithm of x.
If x is +-0, a pole error occurs and log(), logf(), and logl() return
-HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respectively.
For finite values of x that are less than 0, or if x is -Inf, a
domain error occurs and a NaN is returned.
If x is NaN, a NaN is returned.
If x is 1, +0 is returned.
If x is +Inf, x is returned.
For exceptional cases, matherr(3M) tabulates the values to be
returned by log() as specified by SVID3 and XPG3.
ERRORS
These functions will fail if:
Domain Error
The finite value of x is negative, or x is -Inf.
If the integer expression (math_errhandling &
MATH_ERREXCEPT) is non-zero, the invalid floating-
point exception is raised.
The log() function sets errno to EDOM if the value of
x is negative.
Pole Error
The value of x is 0.
If the integer expression (math_errhandling &
MATH_ERREXCEPT) is non-zero, the divide-by-zero
floating-point exception is raised.
USAGE
An application wanting to check for exceptions should call
feclearexcept(FE_ALL_EXCEPT) before calling these functions. On
return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW |
FE_UNDERFLOW) is non-zero, an exception has been raised. An
application should either examine the return value or check the
floating point exception flags to detect exceptions.
An application can also set errno to 0 before calling log(). On
return, if errno is non-zero, an error has occurred. The logf() and
logl() functions do not set errno.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
+----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+----------------------------+-----------------------------+
|Interface Stability | Standard |
+----------------------------+-----------------------------+
|MT-Level | MT-Safe |
+----------------------------+-----------------------------+
SEE ALSO
math.h(3HEAD), exp(3M), feclearexcept(3M), fetestexcept(3M),
isnan(3M), log10(3M), log1p(3M), matherr(3M), attributes(7),
standards(7)
SunOS 5.11 July 12, 2006 LOG(3M)