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logbf (3)
  • logbf (3) ( FreeBSD man: Библиотечные вызовы )
  • >> logbf (3) ( Linux man: Библиотечные вызовы )
  • logbf (3) ( POSIX man: Библиотечные вызовы )
  •  

    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(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE; or cc -std=c99
    logbf(), logbl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99  

    DESCRIPTION

    These functions extract the exponent from the internal floating-point representation of x and return it as a floating-point value. The integer 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.  

    CONFORMING TO

    C99, POSIX.1-2001.  

    SEE ALSO

    ilogb(3), log(3)  

    COLOPHON

    This page is part of release 3.14 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    RETURN VALUE
    ERRORS
    CONFORMING TO
    SEE ALSO
    COLOPHON


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