Tribblix: manual page: log1p.3m

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 log(e)(1.0 + x).

RETURN VALUES

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.

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
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 log1p(). On
return, if errno is non-zero, an error has occurred. The log1pf() and
log1pl() functions do not set errno.

ATTRIBUTES