.\"
.\" Copyright (c) 2025 Robert Clausecker <fuz@FreeBSD.org>
.\"
.\" SPDX-License-Identifier: BSD-2-Clause
.\"
.Dd November 9, 2025
.Dt STDC_BIT_FLOOR 3
.Os
.Sh NAME
.Nm stdc_bit_floor
.Nd round down to the previous power of\~2
.Sh SYNOPSIS
.Lb libc
.In stdbit.h
.Ft unsigned char
.Fn stdc_bit_floor_uc "unsigned char value"
.Ft unsigned short
.Fn stdc_bit_floor_us "unsigned short value"
.Ft unsigned int
.Fn stdc_bit_floor_ui "unsigned int value"
.Ft unsigned long
.Fn stdc_bit_floor_ul "unsigned long value"
.Ft unsigned long long
.Fn stdc_bit_floor_ull "unsigned long long value"
.Ft typeof Ns Pq Em value
.Fn stdc_bit_floor "value"
.Sh DESCRIPTION
The
.Nm stdc_bit_floor_ Ns Em type Ns ()
family of functions rounds
.Fa value
down to the previous power of\~2, 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_bit_floor "value"
type-generic macro picks the appropriate
.Nm stdc_bit_floor_ Ns Em type Ns ()
function based on the type of
.Fa value .
.Sh RETURN VALUES
Returns
.Fa value
round down to the previous power of\~2.
If
.Fa value
is equal to zero,
zero is returned.
.Sh SEE ALSO
.Xr stdbit 3 ,
.Xr stdc_bit_ceil 3
.Sh STANDARDS
The
.Nm stdc_bit_floor_ Ns Em type Ns ()
family of functions and the
.Fn stdc_bit_floor
type-generic macro conform to
.St -isoC-2023 .
.Sh HISTORY
The
.Nm stdc_bit_floor_ Ns Em type Ns ()
family of functions and the
.Fn stdc_bit_floor
type-generic macro were added in
.Fx 15.1.
.Sh AUTHOR
.An Robert Clausecker Aq Mt fuz@FreeBSD.org