logb(3p) — Linux manual page

PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

LOGB(3P)                POSIX Programmer's Manual               LOGB(3P)

PROLOG         top

       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.

NAME         top

       logb, logbf, logbl — radix-independent exponent

SYNOPSIS         top

       #include <math.h>

       double logb(double x);
       float logbf(float x);
       long double logbl(long double x);

DESCRIPTION         top

       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.

RETURN VALUE         top

       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.

ERRORS         top

       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.

EXAMPLES         top

       None.

APPLICATION USAGE         top

       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         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       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)

COPYRIGHT         top

       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)