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.Dd October 27, 2024
.Dt STDC_HAS_SINGLE_BIT 3C
.Os
.Sh NAME
.Nm stdc_has_single_bit ,
.Nm stdc_has_single_bit_uc ,
.Nm stdc_has_single_bit_us ,
.Nm stdc_has_single_bit_ui ,
.Nm stdc_has_single_bit_ul ,
.Nm stdc_has_single_bit_ull
.Nd determine if only one bit is set
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdbit.h
.Ft bool
.Fo stdc_has_single_bit
.Fa "generic_value_type value"
.Fc
.Ft bool
.Fo stdc_has_single_bit_uc
.Fa "unsigned char value"
.Fc
.Ft bool
.Fo stdc_has_single_bit_us
.Fa "unsigned short value"
.Fc
.Ft bool
.Fo stdc_has_single_bit_ui
.Fa "unsigned int value"
.Fc
.Ft bool
.Fo stdc_has_single_bit_ul
.Fa "unsigned long value"
.Fc
.Ft bool
.Fo stdc_has_single_bit_ull
.Fa "unsigned long long value"
.Fc
.Sh DESCRIPTION
The
.Fn stdc_has_single_bit
family of functions determines whether the value has only a single bit
set.
.Fa value .
The function returns
.Dv true
if there is exactly one bit whose value is set to one in
.Fa value .
.Pp
The
.Fn stdc_has_single_bit
function is generic and will operate on all 8, 16, 32, and 64-bit
unsigned integers; however, it is only available in C23.
The other functions all operate on a specific integer type, but
otherwise behave the same and are available regardless of the C language
version.
.Sh RETURN VALUES
The functions in the
.Fn stdc_has_single_bit
family return
.Dv true
if exactly one bit is set in
.Fa value .
Otherwise,
.Dv false
is returned.
These functions cannot fail.
.Sh EXAMPLES
.Sy Example 1
Printing whether only a single bit is set.
.Bd -literal
#include <stdbit.h>
#include <stdio.h>
#include <limits.h>

int
main(void)
{
	printf("%s %s %s %s\en",
	    stdc_has_single_bit_uc(0x23) ? "true" : "false",
	    stdc_has_single_bit_us(0x0080) ? "true" : "false",
	    stdc_has_single_bit_ui(0x81941b23) ? "true" : "false",
	    stdc_has_single_bit_ull(0x00200000000000000) ?
	    "true" : "false");
	return (0);
}
.Ed
.Pp
When compiled and run, this produces:
.Bd -literal -offset indent
$ ./a.out
false true false true
.Ed
.Sh INTERFACE STABILITY
.Sy Committed
.Sh MT-LEVEL
.Sy Async-Signal-Safe
.Sh SEE ALSO
.Xr stdc_bit_ceil 3C ,
.Xr stdc_bit_floor 3C ,
.Xr stdc_bit_width 3C ,
.Xr stdc_count_ones 3C ,
.Xr stdc_count_zeros 3C ,
.Xr stdc_first_leading_one 3C ,
.Xr stdc_first_leading_zero 3C ,
.Xr stdc_first_trailing_one 3C ,
.Xr stdc_first_trailing_zero 3C ,
.Xr stdc_leading_ones 3C ,
.Xr stdc_leading_zeros 3C ,
.Xr stdc_trailing_ones 3C ,
.Xr stdc_trailing_zeros 3C ,
.Xr stdbit.h 3HEAD