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stdc_leading_zeros

From cppreference.net
C
Numerics
Bit manipulation
定义于头文件 <stdbit.h>
unsigned int stdc_leading_zeros_uc ( unsigned char value ) [ [ unsequenced ] ] ;
(1) (C23 起)
unsigned int stdc_leading_zeros_us ( unsigned short value ) [ [ unsequenced ] ] ;
(2) (C23 起)
unsigned int stdc_leading_zeros_ui ( unsigned int value ) [ [ unsequenced ] ] ;
(3) (C23 起)
unsigned int stdc_leading_zeros_ul ( unsigned long int value ) [ [ unsequenced ] ] ;
(4) (C23 起)
unsigned int stdc_leading_zeros_ull ( unsigned long long int value ) [ [ unsequenced ] ] ;
(5) (C23 起)
#define stdc_leading_zeros( value )

// 暴露接口：

generic_return_type stdc_leading_zeros ( generic_value_type value ) [ [ unsequenced ] ] ;
(6) (C23 起)
1-5) 返回从最高有效位开始， value 中连续 ​ 0 ​ 位的数量。
6) 泛型函数（通过其 generic_value_type 参数标识）将根据输入值的类型返回适当结果，前提是该类型为以下之一：
  • 标准无符号整数类型（不包括 bool ）；
  • 扩展无符号整数类型；
  • 或位精确无符号整数类型，其宽度需匹配标准或扩展整数类型（不包括 bool ）。
generic_return_type 应为能够表示计算结果的合适大型无符号整数类型。

目录

参数

值 - 无符号整数类型的值

返回值

从最高有效位开始， value 中连续 ​ 0 ​ 比特位的数量。

示例

运行此代码 
#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;
    }
}

输出： 

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

参见

(C23)
从最高有效位开始查找第一个 ​ 0 ​ 位的位置
(泛型函数宏)
(C23)
计算无符号整数中 ​ 0 ​ 位的数量
(泛型函数宏)
(C23)
从最高有效位开始计算连续 1 位的数量
(泛型函数宏)
C++ 文档 关于 countl_zero