NAME

stdc_bit_width, stdc_bit_width_uc, stdc_bit_width_us, stdc_bit_width_ui, stdc_bit_width_ul, stdc_bit_width_ull — determine minimum bit width

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <stdbit.h>

unsigned int
stdc_bit_width(generic_value_type value);

unsigned int
stdc_bit_width_uc(unsigned char value);

unsigned int
stdc_bit_width_us(unsigned short value);

unsigned int
stdc_bit_width_ui(unsigned int value);

unsigned int
stdc_bit_width_ul(unsigned long value);

unsigned int
stdc_bit_width_ull(unsigned long long value);

DESCRIPTION

The stdc_bit_width() family of functions returns the minimum number of bits required to store value. This is calculated by taking the log base 2 of value and adding 1; however, if value is 0, then the function returns 0. The 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.

RETURN VALUES

The functions in the stdc_bit_width() family returns the minimum number of bits required to hold value. These functions cannot fail.

EXAMPLES

Example 1 Printing the minimum bit width.

#include <stdbit.h>
#include <stdio.h>
#include <limits.h>

int
main(void)
{
	printf("0x%x 0x%x 0x%x 0x%x\n",
	    stdc_bit_width_uc(0x95),
	    stdc_bit_width_us(0xff6),
	    stdc_bit_width_ui(UINT32_MAX),
	    stdc_bit_width_ull(0));
	return (0);
}

When compiled and run, this produces:

$ ./a.out
0x8 0xc 0x20 0x0

INTERFACE STABILITY

Committed

MT-LEVEL

Async-Signal-Safe