NAME

stdc_count_ones, stdc_count_ones_uc, stdc_count_ones_us, stdc_count_ones_ui, stdc_count_ones_ul, stdc_count_ones_ull — count one bits

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <stdbit.h>

unsigned int
stdc_count_ones(generic_value_type value);

unsigned int
stdc_count_ones_uc(unsigned char value);

unsigned int
stdc_count_ones_us(unsigned short value);

unsigned int
stdc_count_ones_ui(unsigned int value);

unsigned int
stdc_count_ones_ul(unsigned long value);

unsigned int
stdc_count_ones_ull(unsigned long long value);

DESCRIPTION

The stdc_count_ones() family of functions returns the number of one bits present in value. These functions are sometimes referred to as a population count.

The stdc_count_ones() 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_count_ones() family always return the number of one bits in value. These functions cannot fail.

EXAMPLES

Example 1 Printing the total number of one bits.

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

int
main(void)
{
	printf("0x%x 0x%x 0x%x 0x%x\n",
	    stdc_count_ones_uc(0x42),
	    stdc_count_ones_us(0xa22b),
	    stdc_count_ones_ui(UINT32_MAX),
	    stdc_count_ones_ull(0));
	return (0);
}

When compiled and run, this produces:

$ ./a.out
0x2 0x7 0x20 0x0

INTERFACE STABILITY

Committed

MT-LEVEL

Async-Signal-Safe