NAME
log1p, log1pf, log1pl - compute a natural logarithm
SYNOPSIS
#include <math.h>
double log1p(double x);
float log1pf(float x);
long double log1pl(long double x);
DESCRIPTION
These functions shall compute log_e(1.0 + x).
An application wishing to check for error situations should set errno
to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these
functions. On return, if errno is non-zero or fetestexcept(FE_INVALID
| FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has
occurred.
RETURN VALUE
Upon successful completion, these functions shall return the natural
logarithm of 1.0 + x.
If x is -1, a pole error shall occur and log1p(), log1pf(), and
log1pl() shall 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 shall occur, and either a NaN (if supported), or an
implementation-defined value shall be returned.
If x is NaN, a NaN shall be returned.
If x is ±0, or +Inf, x shall be returned.
If x is subnormal, a range error may occur and x should be returned.
ERRORS
These functions shall fail if:
Domain Error
The finite value of x is less than -1, or x is -Inf.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then errno shall be set to [EDOM]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid
floating-point exception shall be raised.
Pole Error
The value of x is -1.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then errno shall be set to [ERANGE]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-
zero floating-point exception shall be raised.
These functions may fail if:
Range Error
The value of x is subnormal.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then errno shall be set to [ERANGE]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow
floating-point exception shall be raised.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
On error, the expressions (math_errhandling & MATH_ERRNO) and
(math_errhandling & MATH_ERREXCEPT) are independent of each other, but
at least one of them must be non-zero.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
feclearexcept() , fetestexcept() , log() , the Base Definitions volume
of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions
for Mathematical Functions, <math.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .