function
<cmath> <ctgmath>

# log2

```     double log2  (double x);
float log2f (float x);
long double log2l (long double x);
```
```     double log2 (double x);
float log2 (float x);
long double log2 (long double x);
double log2 (T x);           // additional overloads for integral types```
Compute binary logarithm
Returns the binary (base-2) logarithm of x.

Header <tgmath.h> provides a type-generic macro version of this function.
Additional overloads are provided in this header (`<cmath>`) for the integral types: These overloads effectively cast x to a `double` before calculations (defined for T being any integral type).

### Parameters

x
Value whose logarithm is calculated.
If the argument is negative, a domain error occurs.

### Return Value

The binary logarithm of x: `log2x`.
If x is negative, it causes a domain error:
If x is zero, it may cause a pole error (depending on the library implementation).

If a domain error occurs:
- And math_errhandling has MATH_ERRNO set: the global variable errno is set to EDOM.
- And math_errhandling has MATH_ERREXCEPT set: FE_INVALID is raised.

If a pole error occurs:
- And math_errhandling has MATH_ERRNO set: the global variable errno is set to ERANGE.
- And math_errhandling has MATH_ERREXCEPT set: FE_DIVBYZERO is raised.

### Example

 ``123456789101112`` ``````/* log2 example */ #include /* printf */ #include /* log2 */ int main () { double param, result; param = 1024.0; result = log2 (param); printf ("log2 (%f) = %f.\n", param, result ); return 0; }``````

Output:
 ``` log2 (1024.000000) = 10.000000 ```