ilogb() function in C++ STL
The ilogb(x) function in C++ STL returns the integral part of the logarithm of |x|, by using the FLT_RADIX as base for the logarithm. In general, the value of FLT_RADIX is 2, so ilogb() is equivalent to ilog2()(for positive values only).
Syntax:
ilogb(x)
Parameter: The function accepts a single mandatory parmaeter x whose ilogb() is to be calculated. The data-type can be of double, float, long double or int.
Return Value: The function returns an integral part of the logarithm of |x|, using FLT_RADIX as base for the logarithm. The function returns three exception values:
- If the argument is NaN, it returns FP_LOGBNAN.
- If the argument is infinite, it returns INT_MAX
- If the argument is 0, it returns FP_LOGB0.
Below programs illustrate the above function:
Program 1:
// C++ program to illustrate the ilogb()// function when input is an integer#include <cfloat>#include <cmath>#include <iostream> using namespace std; int main(){ int result, x = 25; // Function to calculate ilogb(25) result = ilogb(x); cout << "ilogb (" << x << ") = " << result << endl; // Function to calculate ilogb(50) x = 50; result = ilogb(x); cout << "ilogb (" << x << ") = " << result << endl; return 0;} |
Output:
ilogb (25) = 4 ilogb (50) = 5
Program 2:
Program for non-integral type
// C++ program to illustrate the ilogb()// function when input is a double value#include <cfloat>#include <cmath>#include <iostream> using namespace std; int main(){ int result, x = 11.11; result = ilogb(x); cout << "ilogb (" << x << ") = " << result << endl; x = 41.11; result = ilogb(x); cout << "ilogb (" << x << ") = " << result << endl; return 0;} |
Output:
ilogb (11) = 3 ilogb (41) = 5
Program 3:
// C++ program to illustrate the ilogb()// function when input is 0#include <cfloat>#include <cmath>#include <iostream>#include <iostream> using namespace std; int main(){ int result, x = 0; result = ilogb(x); cout << "ilogb (" << x << ") = " << result << endl; return 0;} |
Output:
ilogb (0) = -2147483648
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