stdc_leading_zeros

Header: <stdbit.h>

1-5) Returns the number of consecutive 0 bits in the value, starting from the most significant bit.

# Declarations

unsigned int stdc_leading_zeros_uc( unsigned char value ) [[unsequenced]];

(since C23)

unsigned int stdc_leading_zeros_us( unsigned short value ) [[unsequenced]];

(since C23)

unsigned int stdc_leading_zeros_ui( unsigned int value ) [[unsequenced]];

(since C23)

unsigned int stdc_leading_zeros_ul( unsigned long int value ) [[unsequenced]];

(since C23)

unsigned int stdc_leading_zeros_ull( unsigned long long int value ) [[unsequenced]];

(since C23)

#define stdc_leading_zeros( value )
// exposed interface:
generic_return_type stdc_leading_zeros( generic_value_type value ) [[unsequenced]];

(since C23)

# Parameters

value: value of unsigned integer type

# Return value

The number of consecutive 0 bits in the value, starting from the most significant bit.

# Example

#include <limits.h>
#include <stdbit.h>
#include <stdint.h>
#include <stdio.h>
 
#define bits_num(value) (sizeof(value) * CHAR_BIT)
 
#define bin_impl(T, suffix) \
const char* bin_##suffix(T x) \
{ \
    static char buf[bits_num(x) * CHAR_BIT + 1]; \
    for (T i = 0, mask = ((T)1 << (bits_num(x) - 1)); mask; mask >>= 1) \
        buf[i++] = x & mask ? '1' : '0'; \
    buf[bits_num(x)] = '\0'; \
    return buf; \
}
 
bin_impl(uint8_t, u8)
bin_impl(uint16_t, u16)
bin_impl(uint32_t, u32)
bin_impl(uint64_t, u64)
 
#define bin(x) _Generic((x), \
    uint8_t: bin_u8, uint16_t: bin_u16, uint32_t: bin_u32, default: bin_u64)(x)
 
int main()
{
    puts("uint8_t:");
    for (uint8_t x = 0b11000000; ; x >>= 1)
    {
        printf("x = [%s], leading zeros: %d\n", bin(x), stdc_leading_zeros(x));
        if (!x)
            break;
    }
 
    puts("uint16_t:");
    for (uint16_t x = 0b11000000; ; x >>= 1)
    {
        printf("x = [%s], leading zeros: %d\n", bin(x), stdc_leading_zeros(x));
        if (!x)
            break;
    }
}

# See also

C++ documentation