stdc_leading_zeros
From cppreference.com
| Defined in header <stdbit.h>
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unsigned int stdc_leading_zeros_uc( unsigned char value ) [[unsequenced]];
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(1) | (since C23) |
unsigned int stdc_leading_zeros_us( unsigned short value ) [[unsequenced]];
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(2) | (since C23) |
unsigned int stdc_leading_zeros_ui( unsigned int value ) [[unsequenced]];
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(3) | (since C23) |
unsigned int stdc_leading_zeros_ul( unsigned long int value ) [[unsequenced]];
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(4) | (since C23) |
unsigned int stdc_leading_zeros_ull( unsigned long long int value ) [[unsequenced]];
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(5) | (since C23) |
#define stdc_leading_zeros( value )
// exposed interface:
generic_return_type stdc_leading_zeros( generic_value_type value ) [[unsequenced]];
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(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.
generic_return_type shall be a suitable large unsigned integer type capable of representing the computed result.Contents
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
finds the first position of 0 bit, starting from the most significant bit(type-generic function macro) | |
(C23) |
counts the number of 0 bits in an unsigned integer(type-generic function macro) |
(C23) |
counts the number of consecutive 1 bits, starting from the most significant bit(type-generic function macro) |
C++ documentation for countl_zero
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