NAME

stdc_leading_zeros, stdc_leading_zeros_uc, stdc_leading_zeros_us, stdc_leading_zeros_ui, stdc_leading_zeros_ul, stdc_leading_zeros_ull — count consecutive leading zero bits

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <stdbit.h>

unsigned int
stdc_leading_zeros(generic_value_type value);

unsigned int
stdc_leading_zeros_uc(unsigned char value);

unsigned int
stdc_leading_zeros_us(unsigned short value);

unsigned int
stdc_leading_zeros_ui(unsigned int value);

unsigned int
stdc_leading_zeros_ul(unsigned long value);

unsigned int
stdc_leading_zeros_ull(unsigned long long value);

DESCRIPTION

The stdc_leading_zeros() family of functions counts the number of consecutive zero bits present in value starting at the most significant bit.

The stdc_leading_zeros() 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.

Note that promoting an integer from one type to another increases the quantity of leading zeros, thus increasing the return value.

RETURN VALUES

The functions in the stdc_leading_zeros() family always return the number of leading zeros found in value. These functions cannot fail.

EXAMPLES

Example 1 Printing the number of leading zeros.

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

int
main(void)
{
	printf("0x%x 0x%x 0x%x 0x%x\n", stdc_leading_zeros_uc(0x23),
	    stdc_leading_zeros_us(0x23), stdc_leading_zeros_ui(UINT32_MAX),
	    stdc_leading_zeros_ull(0));
	return (0);
}

When compiled and run, this produces:

$ ./a.out
0x2 0xa 0x0 0x40

INTERFACE STABILITY

Committed

MT-LEVEL

Async-Signal-Safe