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logbl (3)
  • logbl (3) ( Linux man: Библиотечные вызовы )
  • >> logbl (3) ( POSIX man: Библиотечные вызовы )
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    NAME

    logb, logbf, logbl - radix-independent exponent
     
    

    SYNOPSIS

    #include <math.h>

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

    DESCRIPTION

    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 IEEE Std 1003.1-2001 defers to the ISO C standard.

    These functions shall compute the exponent of x, which is the integral part of log_r |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

    Upon successful completion, these functions shall return the exponent of x.

    If x is ±0, a pole error shall occur and logb(), logbf(), and logbl() shall return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respectively.

    If x is NaN, a NaN shall be returned.

    If x is ±Inf, +Inf shall be returned.  

    ERRORS

    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.

    The following sections are informative.  

    EXAMPLES

    None.  

    APPLICATION USAGE

    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

    None.  

    FUTURE DIRECTIONS

    None.  

    SEE ALSO

    feclearexcept() , fetestexcept() , ilogb() , scalb() , the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for Mathematical Functions, <float.h>, <math.h>  

    COPYRIGHT

    Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .


     

    Index

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


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