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.Dd October 27, 2024
.Dt STDC_LEADING_ZEROS 3C
.Os
.Sh NAME
.Nm stdc_leading_zeros ,
.Nm stdc_leading_zeros_uc ,
.Nm stdc_leading_zeros_us ,
.Nm stdc_leading_zeros_ui ,
.Nm stdc_leading_zeros_ul ,
.Nm stdc_leading_zeros_ull
.Nd count consecutive leading zero bits
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdbit.h
.Ft "unsigned int"
.Fo stdc_leading_zeros
.Fa "generic_value_type value"
.Fc
.Ft "unsigned int"
.Fo stdc_leading_zeros_uc
.Fa "unsigned char value"
.Fc
.Ft "unsigned int"
.Fo stdc_leading_zeros_us
.Fa "unsigned short value"
.Fc
.Ft "unsigned int"
.Fo stdc_leading_zeros_ui
.Fa "unsigned int value"
.Fc
.Ft "unsigned int"
.Fo stdc_leading_zeros_ul
.Fa "unsigned long value"
.Fc
.Ft "unsigned int"
.Fo stdc_leading_zeros_ull
.Fa "unsigned long long value"
.Fc
.Sh DESCRIPTION
The
.Fn stdc_leading_zeros
family of functions counts the number of consecutive zero bits present in
.Fa value
starting at the most significant bit.
.Pp
The
.Fn 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.
.Pp
Note that promoting an integer from one type to another increases the
quantity of leading zeros, thus increasing the return value.
.Sh RETURN VALUES
The functions in the
.Fn stdc_leading_zeros
family always return the number of leading zeros found in
.Fa value .
These functions cannot fail.
.Sh EXAMPLES
.Sy Example 1
Printing the number of leading zeros.
.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_leading_zeros_uc(0x23),
	    stdc_leading_zeros_us(0x23), stdc_leading_zeros_ui(UINT32_MAX),
	    stdc_leading_zeros_ull(0));
	return (0);
}
.Ed
.Pp
When compiled and run, this produces:
.Bd -literal -offset indent
$ ./a.out
0x2 0xa 0x0 0x40
.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_has_single_bit 3C ,
.Xr stdc_leading_ones 3C ,
.Xr stdc_trailing_ones 3C ,
.Xr stdc_trailing_zeros 3C ,
.Xr stdbit.h 3HEAD