stdc_leading_zeros - cppreference.com (original) (raw)
| 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.
- The type-generic function (marked by its
generic_value_typeargument) 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.
[edit] Parameters
| value | - | value of unsigned integer type |
|---|
[edit] Return value
The number of consecutive 0 bits in the value, starting from the most significant bit.
[edit] 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;
}
}
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