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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
ILOGB(3P) POSIX Programmer's Manual ILOGB(3P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
delim $$
ilogb, ilogbf, ilogbl — return an unbiased exponent
#include <math.h>
int ilogb(double x);
int ilogbf(float x);
int ilogbl(long double x);
The functionality described on this reference page is aligned with
the ISO C standard. Any conflict between the requirements described
here and the ISO C standard is unintentional. This volume of
POSIX.1‐2008 defers to the ISO C standard.
These functions shall return the exponent part of their argument x.
Formally, the return value is the integral part of $log sub{r}|x|$ as
a signed integral value, for non-zero x, where r is the radix of the
machine's floating-point arithmetic, which is the value of FLT_RADIX
defined in <float.h>.
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 exponent
part of x as a signed integer value. They are equivalent to calling
the corresponding logb() function and casting the returned value to
type int.
If x is 0, the value FP_ILOGB0 shall be returned. On XSI-conformant
systems, a domain error shall occur;
otherwise, a domain error may occur.
If x is ±Inf, the value {INT_MAX} shall be returned. On XSI-
conformant systems, a domain error shall occur;
otherwise, a domain error may occur.
If x is a NaN, the value FP_ILOGBNAN shall be returned. On XSI-
conformant systems, a domain error shall occur;
otherwise, a domain error may occur.
If the correct value is greater than {INT_MAX}, a domain error shall
occur and an unspecified value shall be returned. On XSI-conformant
systems, a domain error shall occur and {INT_MAX} shall be returned.
If the correct value is less than {INT_MIN}, a domain error shall
occur and an unspecified value shall be returned. On XSI-conformant
systems, a domain error shall occur and {INT_MIN} shall be returned.
These functions shall fail if:
Domain Error
The correct value is not representable as an integer.
The x argument is zero, NaN, or ±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.
These functions may fail if:
Domain Error
The x argument is zero, NaN, or ±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.
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.
The errors come from taking the expected floating-point value and
converting it to int, which is an invalid operation in
IEEE Std 754‐1985 (since overflow, infinity, and NaN are not
representable in a type int), so should be a domain error.
There are no known implementations that overflow. For overflow to
happen, {INT_MAX} must be less than LDBL_MAX_EXP*log2(FLT_RADIX) or
{INT_MIN} must be greater than LDBL_MIN_EXP*log2(FLT_RADIX) if
subnormals are not supported, or {INT_MIN} must be greater than
(LDBL_MIN_EXP-LDBL_MANT_DIG)*log2(FLT_RADIX) if subnormals are
supported.
None.
feclearexcept(3p), fetestexcept(3p), logb(3p), scalbln(3p)
The Base Definitions volume of POSIX.1‐2008, Section 4.19, Treatment
of Error Conditions for Mathematical Functions, float.h(0p),
math.h(0p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 ILOGB(3P)
Pages that refer to this page: math.h(0p), expm1(3p), logb(3p)