Compute the base-2 logarithm of a number
#include <math.h> double log2( double x ); float log2f( float x ); long double log2l( long double x );
The log2(), log2f(), and log2l() functions compute the base-2 logarithm of x:
log2x
To check for error situations, use feclearexcept() and fetestexcept(). For example:
The base-2 logarithm of x.
| If x is: | These functions return: | Errors: |
|---|---|---|
| x is ±0.0 | -Inf | FE_DIVBYZERO |
| 1.0 | 0.0 | — |
| Less than 0.0 and finite, or -Inf | NaN | FE_INVALID |
| Inf | Inf | — |
| NaN | NaN | — |
These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.
| Safety: | |
|---|---|
| Cancellation point | No |
| Interrupt handler | No |
| Signal handler | No |
| Thread | Yes |