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man:logbf

LOGB(3) Linux Programmer's Manual LOGB(3)

NAME

     logb, logbf, logbl - get exponent of a floating-point value

SYNOPSIS

     #include <math.h>
     double logb(double x);
     float logbf(float x);
     long double logbl(long double x);
     Link with -lm.
 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
     logb():
         _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
             || _XOPEN_SOURCE >= 500
             || /* Since glibc 2.19: */ _DEFAULT_SOURCE
             || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
     logbf(), logbl():
         _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
             || /* Since glibc 2.19: */ _DEFAULT_SOURCE
             || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

     These  functions  extract the exponent from the internal floating-point
     representation of x and return it as a floating-point value.  The inte-
     ger  constant FLT_RADIX, defined in <float.h>, indicates the radix used
     for the system's floating-point representation.   If  FLT_RADIX  is  2,
     logb(x)  is equal to floor(log2(x)), except that it is probably faster.
     If x is subnormal, logb() returns the exponent x would have if it  were
     normalized.

RETURN VALUE

     On success, these functions return the exponent of x.
     If x is a NaN, a NaN is returned.
     If  x  is  zero,  then  a  pole  error occurs, and the functions return
     -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.
     If x is negative infinity or positive infinity, then positive  infinity
     is returned.

ERRORS

     See  math_error(7) for information on how to determine whether an error
     has occurred when calling these functions.
     The following errors can occur:
     Pole error: x is 0
            A  divide-by-zero  floating-point  exception  (FE_DIVBYZERO)  is
            raised.
     These functions do not set errno.

ATTRIBUTES

     For   an   explanation   of   the  terms  used  in  this  section,  see
     attributes(7).
     allbox; lbw24 lb  lb  l  l  l.   Interface Attribute Value  T{  logb(),
     logbf(), logbl() T}   Thread safety  MT-Safe

CONFORMING TO

     C99, POSIX.1-2001, POSIX.1-2008.

SEE ALSO

     ilogb(3), log(3)

COLOPHON

     This  page  is  part of release 4.16 of the Linux man-pages project.  A
     description of the project, information about reporting bugs,  and  the
     latest     version     of     this    page,    can    be    found    at
     https://www.kernel.org/doc/man-pages/.
                                2017-09-15                           LOGB(3)
/data/webs/external/dokuwiki/data/pages/man/logbf.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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