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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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LOGB(3P) POSIX Programmer's Manual LOGB(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.
logb, logbf, logbl — radix-independent exponent
#include <math.h>
double logb(double x);
float logbf(float x);
long double logbl(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.1‐2017 defers to the ISO C standard.
These functions shall compute the exponent of x, which is the
integral part of logr |x|, as a signed floating-point 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 the
<float.h> header.
If x is subnormal it is treated as though it were normalized;
thus for finite positive x:
1 <= x * FLT_RADIX-logb(x) < FLT_RADIX
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 of x.
If x is ±0, logb(), logbf(), and logbl() shall return -HUGE_VAL,
-HUGE_VALF, and -HUGE_VALL, respectively.
On systems that support the IEC 60559 Floating-Point option, a
pole error shall occur;
otherwise, a pole error may occur.
If x is NaN, a NaN shall be returned.
If x is ±Inf, +Inf shall be returned.
These functions shall fail if:
Pole Error The value of x is ±0.
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:
Pole Error The value of x is 0.
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.
feclearexcept(3p), fetestexcept(3p), ilogb(3p), scalbln(3p)
The Base Definitions volume of POSIX.1‐2017, Section 4.20,
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 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
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 2017 LOGB(3P)
Pages that refer to this page: math.h(0p), ilogb(3p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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