.SH SYNOPSIS
.nf
.B #include <math.h>
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.BI "double log2(double " x );
.BI "float log2f(float " x );
.BI "long double log2l(long double " x );
.fi
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.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
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.BR log2 (),
.BR log2f (),
.BR log2l ():
.SH RETURN VALUE
On success, these functions return the base 2 logarithm of
.IR x .
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For special cases, including where
.I x
is 0, 1, negative, infinity, or NaN, see
.BR math_error (7)
for information on how to determine whether an error has occurred
when calling these functions.
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For a discussion of the errors that can occur for these functions, see
.BR log (3).
.SH ATTRIBUTES
.SH HISTORY
glibc 2.1.
C99, POSIX.1-2001.
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The variant returning
.I double
also conforms to