.\"
.\" Copyright (c) 2025 Robert Clausecker <fuz@FreeBSD.org>
.\"
.\" SPDX-License-Identifier: BSD-2-Clause
.\"
.Dd November 9, 2025
.Dt STDC_HAS_SINGLE_BIT 3
.Os
.Sh NAME
.Nm stdc_has_single_bit
.Nd check for single bit set
.Sh SYNOPSIS
.Lb libc
.In stdbit.h
.Ft bool
.Fn stdc_has_single_bit_uc "unsigned char value"
.Ft bool
.Fn stdc_has_single_bit_us "unsigned short value"
.Ft bool
.Fn stdc_has_single_bit_ui "unsigned int value"
.Ft bool
.Fn stdc_has_single_bit_ul "unsigned long value"
.Ft bool
.Fn stdc_has_single_bit_ull "unsigned long long value"
.Ft bool
.Fn stdc_has_single_bit "value"
.Sh DESCRIPTION
The
.Nm stdc_has_single_bit_ Ns Em type Ns ()
family of functions checks if there is exactly one bit
set in
.Fa value ,
where
.Fa value
is of type
.Va unsigned char ,
.Va unsigned short ,
.Va unsigned int ,
.Va unsigned long ,
or
.Va unsigned long long
for
.Em type
being
.Sy uc ,
.Sy us ,
.Sy ui ,
.Sy ul ,
or
.Sy ull
respectively.
The
.Fn stdc_has_single_bit "value"
type-generic macro picks the appropriate
.Nm stdc_has_single_bit_ Ns Em type Ns ()
function based on the type of
.Fa value .
.Pp
The functions in this family behave similarly to the
.Fn powerof2 "value"
macro of
.In sys/param.h ,
but differ when
.Fa value
is zero: while
.Fn powerof2
considers zero to be a power of two,
.Fn stdc_has_single_bit
does not.
.Sh RETURN VALUES
Returns
.Sy true
if exactly one bit is set in
.Fa value ,
otherwise returns
.Sy false .
I.\^e. the function determines if
.Fa value
is a power of two.
.Sh SEE ALSO
.Xr stdbit 3 ,
.Xr stdc_count_ones 3
.Sh STANDARDS
The
.Nm stdc_has_single_bit_ Ns Em type Ns ()
family of functions and the
.Fn stdc_has_single_bit
type-generic macro conform to
.St -isoC-2023 .
.Sh HISTORY
The
.Nm stdc_has_single_bit_ Ns Em type Ns ()
family of functions and the
.Fn stdc_has_single_bit
type-generic macro were added in
.Fx 15.1.
.Sh AUTHOR
.An Robert Clausecker Aq Mt fuz@FreeBSD.org