LOG10(P) POSIX Programmer's Manual LOG10(P)NAME
log10, log10f, log10l - base 10 logarithm function
SYNOPSIS
#include <math.h>
double log10(double x);
float log10f(float x);
long double log10l(long double x);
DESCRIPTION
These functions shall compute the base 10 logarithm of their argument
x, log_10(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 base 10
logarithm of x.
If x is ±0, a pole error shall occur and log10(), log10f(), and
log10l() shall return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respec‐
tively.
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, +Inf shall be returned.
ERRORS
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.
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 ALSOfeclearexcept() , fetestexcept() , isnan() , log() , pow() , 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 .
IEEE/The Open Group 2003 LOG10(P)
