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

    NAME

    logb, logbf, logbl - radix-independent exponent
     
    

    SYNOPSIS

    c99 [ flag... ] file... -lm [ library... ]
    #include <math.h>
    
    double logb(double x);
    

    float logbf(float x);
    

    long double logbl(long double x);
    

    cc [ flag... ] file... -lm [ library... ]
    #include <math.h>
    
    double logb(double x);
    

    float logbf(float x);
    

    long double logbl(long double x);
    

     

    DESCRIPTION

    These functions 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.  

    RETURN VALUES

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

    If x is subnormal:

    o For SUSv3-conforming applications compiled with the c99 compiler driver (see standards(5)), the exponent of x as if x were normalized is returned.
    o Otherwise, if compiled with the cc compiler driver, -1022, -126, and -16382 are returned for logb(), logbf(), and logbl(), respectively.

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

    If x is NaN, a NaN is returned.

    If x is ±Inf, +Inf is returned.  

    ERRORS

    These functions will fail if:

    Pole Error

    The value of x is ±0.

    If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the divide-by-zero floating-point exception is raised.

    The logb() function sets errno to EDOM if the value of x is 0.

     

    USAGE

    An application wanting to check for exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception has been raised. An application should either examine the return value or check the floating point exception flags to detect exceptions.

    An application can also set errno to 0 before calling logb(). On return, if errno is non-zero, an error has occurred. The logbf() and logbl() functions do not set errno.  

    ATTRIBUTES

    See attributes(5) for descriptions of the following attributes:

    ATTRIBUTE TYPEATTRIBUTE VALUE

    Interface StabilityStandard

    MT-Level

     

    SEE ALSO

    feclearexcept(3M), fetestexcept(3M), ilogb(3M), math.h(3HEAD), matherr(3M), scalb(3M), attributes(5), standards(5)


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    RETURN VALUES
    ERRORS
    USAGE
    ATTRIBUTES
    SEE ALSO


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