LOG(3M) | Mathematical Library Functions | LOG(3M) |

log, logf, logl - natural logarithm function

c99 [flag... ]file...-lm[library... ] #include <math.h>doublelog(doublex);

floatlogf(floatx);

long doublelogl(long doublex);

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)

July 12, 2006 | SunOS 5.11 |