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.1‐2008 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.1‐2008, Section 4.19, 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, 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                            LOGB(3P)

Pages that refer to this page: math.h(0p)ilogb(3p)