log1p(3M) Mathematical Library Functions log1p(3M)NAME
log1p, log1pf, log1pl - compute natural logarithm
SYNOPSIS
c99 [ flag... ] file... -lm [ library... ]
#include <math.h>
double log1p(double x);
float log1pf(float x);
long double log1pl(long double x);
DESCRIPTION
These functions compute loge(1.0 + x).
RETURN VALUES
Upon successful completion, these functions return the natural loga‐
rithm 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.
ERRORS
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 float‐
ing-point exception is raised.
USAGE
An application wanting to check for exceptions should call feclearex‐
cept(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.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Standard │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │MT-Safe │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOfeclearexcept(3M), fetestexcept(3M), log(3M), math.h(3HEAD), math‐
err(3M), attributes(5), standards(5)SunOS 5.10 12 Jul 2006 log1p(3M)