log2, log2f, log2l

Article
06/05/2017

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Determines the binary (base-2) logarithm of the specified value.

Syntax

double log2(  
   double x  
);  
  
float log2(  
   float x  
); //C++ only  
  
long double log2(  
   long double x  
); //C++ only  
  
float log2f(  
   float x  
);  
  
long double log2l(  
   long double x  
);

Parameters

[in] x
The value to determine the base-2 logarithm of.

Return Value

On success, returns return log2 x.

Otherwise, may return one of the following values:

Issue	Return
`x` < 0	NaN
`x` = ±0	-INFINITY
`x` = 1	+0
+INFINITY	+INFINITY
NaN	NaN
domain error	NaN
pole error	-HUGE_VAL, -HUGE_VALF, or -HUGE_VALL

Errors are reported as specified in _matherr.

Remarks

If x is an integer, this function essentially returns the zero-based index of the most significant 1 bit of x.

Requirements

Function	C header	C++ header
`log2`, `log2f`, `log2l`	<math.h>	<cmath>

For additional compatibility information, see Compatibility.

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