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.\" Copyright 2024 Oxide Computer Company
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.Dd October 27, 2024
.Dt STDC_BIT_WIDTH 3C
.Os
.Sh NAME
.Nm stdc_bit_width ,
.Nm stdc_bit_width_uc ,
.Nm stdc_bit_width_us ,
.Nm stdc_bit_width_ui ,
.Nm stdc_bit_width_ul ,
.Nm stdc_bit_width_ull
.Nd determine minimum bit width
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdbit.h
.Ft "unsigned int"
.Fo stdc_bit_width
.Fa "generic_value_type value"
.Fc
.Ft "unsigned int"
.Fo stdc_bit_width_uc
.Fa "unsigned char value"
.Fc
.Ft "unsigned int"
.Fo stdc_bit_width_us
.Fa "unsigned short value"
.Fc
.Ft "unsigned int"
.Fo stdc_bit_width_ui
.Fa "unsigned int value"
.Fc
.Ft "unsigned int"
.Fo stdc_bit_width_ul
.Fa "unsigned long value"
.Fc
.Ft "unsigned int"
.Fo stdc_bit_width_ull
.Fa "unsigned long long value"
.Fc
.Sh DESCRIPTION
The
.Fn stdc_bit_width
family of functions returns the minimum number of bits required to store
.Fa value .
This is calculated by taking the log base 2 of
.Fa value
and adding 1; however, if
.Fa value
is 0, then the function returns 0.
The
.Fn stdc_bit_width
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_bit_width
family returns the minimum number of bits required to hold
.Fa value .
These functions cannot fail.
.Sh EXAMPLES
.Sy Example 1
Printing the minimum bit width.
.Bd -literal
#include <stdbit.h>
#include <stdio.h>
#include <limits.h>

int
main(void)
{
	printf("0x%x 0x%x 0x%x 0x%x\en",
	    stdc_bit_width_uc(0x95),
	    stdc_bit_width_us(0xff6),
	    stdc_bit_width_ui(UINT32_MAX),
	    stdc_bit_width_ull(0));
	return (0);
}
.Ed
.Pp
When compiled and run, this produces:
.Bd -literal -offset indent
$ ./a.out
0x8 0xc 0x20 0x0
.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_count_ones 3C ,
.Xr stdc_count_zero 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_has_single_bit 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