GCC编译器中三个重要的函数

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1. _builtin_popcount（x）：该函数用于对整数中“1”的个数进行计数

#include <stdio.h>#include <stdlib.h>int main(){    int n = 5;    printf("Count of 1s in binary of %d is %d ",                       n, __builtin_popcount(n));    return 0;}output:Count of 1s in binary of 5 is 2.

2. __builtin_clz(x)：该函数用于对整数中前导“0”的个数进行计数

#include <stdio.h>#include <stdlib.h>int main(){    int n = 16;    printf("Count of leading zeros before 1 in %d is %d",                                    n, __builtin_clz(n));    return 0;}/* * output: * Count of leading zeros before 1 in 16 is 27 */

3. __builtin_ctz(x)：该函数用于对整数中尾随的“0”的个数进行计数

#include <stdio.h>#include <stdlib.h>int main(){    int n = 16;    printf("Count of zeros from last to first occurrence of one is %d",__builtin_ctz(n));    return 0;}/* * output: * Count of zeros from last to first occurrence of one is 4 */

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