log2-log2f-log2l.md

title	description	ms.date	api_name	api_location	api_type	topic_type	ms.assetid
log2, log2f, log2l	API reference for log2, log2f, and log2l; which determine the binary (base-2) logarithm of the specified value.	9/1/2020	log2 log2l log2f _o_log2 _o_log2f _o_log2l	msvcrt.dll msvcr80.dll msvcr90.dll msvcr100.dll msvcr100_clr0400.dll msvcr110.dll msvcr110_clr0400.dll msvcr120.dll msvcr120_clr0400.dll ucrtbase.dll api-ms-win-crt-math-l1-1-0.dll	DLLExport	apiref	94d11b38-70b7-4d3a-94ac-523153c92b2e

log2, log2f, log2l

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
);

#define log2(X) // Requires C11 or higher

Parameters

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

Return value

On success, the functions return the base-2 log of x.

Otherwise, the functions 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.

By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.

Requirements

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

For more compatibility information, see Compatibility.

See also

Alphabetical function reference
exp2, exp2f, exp2l
log, logf, log10, log10f