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:
log_{2}x
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 |