std::logb,std::logbf,std::logbl (3) - Linux Man Pages
Defined in header <cmath>
float logb ( float arg ); (1) (since C++11)
float logbf( float arg );
double logb ( double arg ); (2) (since C++11)
long double logb ( long double arg ); (3) (since C++11)
long double logbl( long double arg );
double logb ( IntegralType arg ); (4) (since C++11)
1-3) Extracts the value of the unbiased radix-independent exponent from the floating-point argument arg, and returns it as a floating-point value.
4) A set of overloads or a function template accepting an argument of any integral_type. Equivalent to (2) (the argument is cast to double).
Formally, the unbiased exponent is the signed integral part of log
r|arg| (returned by this function as a floating-point value), for non-zero arg, where r is std::numeric_limits<T>::radix and T is the floating-point type of arg. If arg is subnormal, it is treated as though it was normalized.
arg - floating point value
If no errors occur, the unbiased exponent of arg is returned as a signed floating-point value.
If a domain error occurs, an implementation-defined value is returned
If a pole error occurs, -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL is returned.
Errors are reported as specified in math_errhandling.
Domain or range error may occur if arg is zero.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
* If arg is ±0, -∞ is returned and FE_DIVBYZERO is raised.
* If arg is ±∞, +∞ is returned
* If arg is NaN, NaN is returned.
* In all other cases, the result is exact (FE_INEXACT is never raised) and the_current_rounding_mode is ignored
POSIX_requires that a pole error occurs if arg is ±0.
The value of the exponent returned by std::logb is always 1 less than the exponent retuned by std::frexp because of the different normalization requirements: for the exponent e returned by std::logb, |arg*r-e
| is between 1 and r (typically between 1 and 2), but for the exponent e returned by std::frexp, |arg*2-e
| is between 0.5 and 1.
Compares different floating-point decomposition functions
// Run this code
frexpl decomposes a number into significand and a power of 2
ilogbl extracts exponent of the number
scalblnl multiplies a number by FLT_RADIX raised to a power