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'\" t
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH log2 3 2025-05-17 "Linux man-pages (unreleased)"
.SH NAME
log2, log2f, log2l \- base-2 logarithmic function
.SH LIBRARY
Math library
.RI ( libm ,\~ \-lm )
.SH SYNOPSIS
.nf
.B #include <math.h>
.P
.BI "double log2(double " x );
.BI "float log2f(float " x );
.BI "long double log2l(long double " x );
.fi
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR log2 (),
.BR log2f (),
.BR log2l ():
.nf
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
.fi
.SH DESCRIPTION
These functions return the base-2 logarithm of
.IR x .
.SH RETURN VALUE
On success, these functions return the base-2 logarithm of
.IR x .
.P
For special cases, including where
.I x
is 0, 1, negative, infinity, or NaN, see
.BR log (3).
.SH ERRORS
See
.BR math_error (7)
for information on how to determine whether an error has occurred
when calling these functions.
.P
For a discussion of the errors that can occur for these functions, see
.BR log (3).
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.na
.nh
.BR log2 (),
.BR log2f (),
.BR log2l ()
T} Thread safety MT-Safe
.TE
.SH STANDARDS
C11, POSIX.1-2008.
.SH HISTORY
glibc 2.1.
C99, POSIX.1-2001.
.P
The variant returning
.I double
also conforms to
SVr4, 4.3BSD.
.SH SEE ALSO
.BR cbrt (3),
.BR clog2 (3),
.BR log (3),
.BR log10 (3),
.BR sqrt (3)
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