.\"
.\" Copyright (c) 2025 Robert Clausecker <fuz@FreeBSD.org>
.\"
.\" SPDX-License-Identifier: BSD-2-Clause
.\"
.Dd November 9, 2025
.Dt STDBIT 3
.Os
.Sh NAME
.Nm stdbit
.Nd bit and byte utilities
.Sh SYNOPSIS
.Lb libc
.In stdbit.h
.Fd #define __STDC_ENDIAN_LITTLE__
.Fd #define __STDC_ENDIAN_BIG__
.Fd #define __STDC_ENDIAN_NATIVE__
.Ft unsigned int
.Fn stdc_count_leading_zeros "value"
.Ft unsigned int
.Fn stdc_count_leading_ones "value"
.Ft unsigned int
.Fn stdc_count_trailing_zeros "value"
.Ft unsigned int
.Fn stdc_count_trailing_ones "value"
.Ft unsigned int
.Fn stdc_first_leading_zero "value"
.Ft unsigned int
.Fn stdc_first_leading_one "value"
.Ft unsigned int
.Fn stdc_first_trailing_zero "value"
.Ft unsigned int
.Fn stdc_first_trailing_one "value"
.Ft unsigned int
.Fn stdc_count_zeros "value"
.Ft unsigned int
.Fn stdc_count_ones "value"
.Ft bool
.Fn stdc_has_single_bit "value"
.Ft unsigned int
.Fn stdc_bit_width "value"
.Ft typeof Ns Pq Em value
.Fn stdc_bit_floor "value"
.Ft typeof Ns Pq Em value
.Fn stdc_bit_ceil "value"
.Sh DESCRIPTION
The
.Dv __STDC_ENDIAN_NATIVE__
macro describes the byte order or endianness of the machine for which the
program is built.
If the machine has big-endian byte order, this macro is equal to
.Dv __STDC_ENDIAN_BIG__ .
If the machine has little-endian byte order, this macro is equal to
.Dv __STDC_ENDIAN_LITTLE__ .
Otherwise, the macro has a value that is equal to neither.
.Pp
The bit and byte utility functions analyze the bits within a datum.
Each function
.Em func
is provided in five variants
.Nm stdc_ Ns Em func Ns Em _ Ns Em type Ns Pq Em 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.
Additionally, for each
.Em func ,
a type-generic macro
.Nm stdc_ Ns Em func Ns Pq Em value
that picks the appropriate function
.Nm stdc_ Ns Em func Ns Em _ Ns Em type Ns Pq Em value
based on the type of
.Fa value
is provided.
.Sh SEE ALSO
.Xr arch 7 ,
.Xr bitstring 3 ,
.Xr ffs 3 ,
.Xr fls 3 ,
.Xr stdc_count_leading_zeros 3 ,
.Xr stdc_count_leading_ones 3 ,
.Xr stdc_count_trailing_zeros 3 ,
.Xr stdc_count_trailing_ones 3 ,
.Xr stdc_first_leading_zero 3 ,
.Xr stdc_first_leading_one 3 ,
.Xr stdc_first_trailing_zero 3 ,
.Xr stdc_first_trailing_one 3 ,
.Xr stdc_count_zeros 3 ,
.Xr stdc_count_ones 3 ,
.Xr stdc_has_single_bit 3 ,
.Xr stdc_bit_width 3 ,
.Xr stdc_bit_floor 3 ,
.Xr stdc_bit_ceil 3
.Sh STANDARDS
The macros and functions of the
.In stdbit.h
header conform to
.St -isoC-2023 .
.Sh HISTORY
The
.In stdbit.h
header and the macros and functions defined therein where added in
.Fx 15.1.
.Sh AUTHOR
.Ah Robert Clausecker Aq Mt fuz@FreeBSD.org