Originální popis anglicky:
log, logf, logl - natural logarithm function
Návod, kniha: POSIX Programmer's Manual
#include <math.h>
double log(double
x);
float logf(float
x);
long double logl(long double
x);
These functions shall compute the natural logarithm of their argument
x,
log_
e(
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.
Upon successful completion, these functions shall return the natural logarithm
of
x.
If
x is ±0, a pole error shall occur and
log(),
logf(), and
logl() shall 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 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 1, +0 shall be returned.
If
x is +Inf,
x shall be returned.
These functions shall fail if:
- Domain Error
- The finite value of x is negative, 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 zero.
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.
The following sections are informative.
None.
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.
None.
None.
exp() ,
feclearexcept() ,
fetestexcept() ,
isnan() ,
log10() ,
log1p() , the Base Definitions volume of
IEEE Std 1003.1-2001, Section 4.18, Treatment of Error
Conditions for Mathematical Functions,
<math.h>
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
.
