LOG1P(3M) | Mathematical Library Functions | LOG1P(3M) |

log1p, log1pf, log1pl - compute natural logarithm

c99 [flag... ]file...-lm[library... ] #include <math.h>doublelog1p(doublex);

floatlog1pf(floatx);

long doublelog1pl(long doublex);

These functions compute log(e)(1.0 + *x*).

Upon successful completion, these functions return the natural
logarithm of 1.0 + *x*.

If *x* is −1, a pole error occurs and **log1p()**,
**log1pf()**, and **log1pl()** return −**HUGE_VAL**,
−**HUGE_VALF**, and −**HUGE_VALL**, respectively.

For finite values of *x* that are less than −1, 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 ±0 or +Inf, *x* is returned.

For exceptional cases, matherr(3M) tabulates the values to
be returned by **log1p()** as specified by SVID3 and XPG3.

These functions will fail if:

**Domain Error**

The finite value of *x* is less than −1, or
*x* is -Inf.

If the integer expression (**math_errhandling** &
**MATH_ERREXCEPT**) is non-zero, the invalid floating-point exception is
raised.

The **log1p()** function sets **errno** to **EDOM** if
the value of *x* is less than −1.

**Pole Error**

The value of *x* is −1.

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
**log1p()**. On return, if **errno** is non-zero, an error has
occurred. The **log1pf()** and **log1pl()** 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), feclearexcept(3M), fetestexcept(3M), log(3M), matherr(3M), attributes(7), standards(7)

July 12, 2006 | SunOS 5.11 |