stdc_leading_zeros

 

C

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Technical Specifications

Symbol index

 

Numerics

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Complex number arithmetic (C99)

Type-generic math (C99)

Bit manipulation (C23)

Checked integer arithmetic (C23)

 

Bit manipulation

Functions

stdc_leading_zeros (C23)

stdc_leading_ones (C23)

stdc_trailing_zeros (C23)

stdc_trailing_ones (C23)

stdc_first_leading_zero (C23)

stdc_first_leading_one (C23)

stdc_first_trailing_zero (C23)

stdc_first_trailing_one (C23)

stdc_count_zeros (C23)

stdc_count_ones (C23)

stdc_has_single_bit (C23)

stdc_bit_width (C23)

stdc_bit_floor (C23)

stdc_bit_ceil (C23)

Macro constants

__STDC_ENDIAN_LITTLE__ __STDC_ENDIAN_BIG__ __STDC_ENDIAN_NATIVE__ (C23)(C23)(C23)

 

Defined in header <stdbit.h>
unsigned int stdc_leading_zeros_uc( unsigned char value ) [[unsequenced]];	(1)	(since C23)
unsigned int stdc_leading_zeros_us( unsigned short value ) [[unsequenced]];	(2)	(since C23)
unsigned int stdc_leading_zeros_ui( unsigned int value ) [[unsequenced]];	(3)	(since C23)
unsigned int stdc_leading_zeros_ul( unsigned long int value ) [[unsequenced]];	(4)	(since C23)
unsigned int stdc_leading_zeros_ull( unsigned long long int value ) [[unsequenced]];	(5)	(since C23)
#define stdc_leading_zeros( value ) // exposed interface: generic_return_type stdc_leading_zeros( generic_value_type value ) [[unsequenced]];	(6)	(since C23)

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

6) The type-generic function (marked by its generic_value_type argument) returns the appropriate value based on the type of the input value, so long as it is a:

• standard unsigned integer type, excluding bool;
• extended unsigned integer type;
• or, bit-precise unsigned integer type whose width matches a standard or extended integer type, excluding bool.

The generic_return_type shall be a suitable large unsigned integer type capable of representing the computed result.

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

Run this code

#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;
    }
}

Output:

uint8_t:
x = [11000000], leading zeros: 0
x = [01100000], leading zeros: 1
x = [00110000], leading zeros: 2
x = [00011000], leading zeros: 3
x = [00001100], leading zeros: 4
x = [00000110], leading zeros: 5
x = [00000011], leading zeros: 6
x = [00000001], leading zeros: 7
x = [00000000], leading zeros: 8
uint16_t:
x = [0000000011000000], leading zeros: 8
x = [0000000001100000], leading zeros: 9
x = [0000000000110000], leading zeros: 10
x = [0000000000011000], leading zeros: 11
x = [0000000000001100], leading zeros: 12
x = [0000000000000110], leading zeros: 13
x = [0000000000000011], leading zeros: 14
x = [0000000000000001], leading zeros: 15
x = [0000000000000000], leading zeros: 16

See also

stdc_first_leading_zero (C23)	finds the first position of ​0​ bit, starting from the most significant bit (type-generic function macro)
stdc_count_zeros (C23)	counts the number of ​0​ bits in an unsigned integer (type-generic function macro)
stdc_leading_ones (C23)	counts the number of consecutive 1 bits, starting from the most significant bit (type-generic function macro)
C++ documentation for countl_zero