这些是GCC编译器中的四个重要的内置函数:
- _builtin_popcount(x):此函数用于对一个整数(设置位)的个数进行计数。
例子:if x = 4 binary value of 4 is 100 Output: No of ones is 1.
// C program to illustrate _builtin_popcount(x) #include
int main() { int n = 5; printf("Count of 1s in binary of %d is %d ", n, __builtin_popcount(n)); return 0; } 输出:Count of 1s in binary of 5 is 2
注意:同样,对于长数据类型和长长数据类型,您可以使用__builtin_popcountl(x)和__builtin_popcountll(x)。
- _builtin_parity(x):此函数用于检查数字的奇偶校验。如果数字具有奇偶校验,则此函数返回true(1),否则返回偶数奇偶的false(0)。
例子:if x = 7 7 has odd no. of 1's in its binary(111). Output: Parity of 7 is 1
// C program to illustrate _builtin_parity(x) #include
int main() { int n = 7; printf("Parity of %d is %d ", n, __builtin_parity(n)); return 0; } 输出:Parity of 7 is 1
注意:同样,对于长数据类型和长长数据类型,您可以使用__builtin_parityl(x)和__builtin_parityll(x)。
- __builtin_clz(x):此函数用于计算整数的前导零。注意:clz =计数前导零
示例:它在第一次出现一个(置位)之前对零的数目进行计数。a = 16 Binary form of 16 is 00000000 00000000 00000000 00010000 Output: 27
// C program to illustrate __builtin_clz(x) #include
int main() { int n = 16; printf("Count of leading zeros before 1 in %d is %d", n, __builtin_clz(n)); return 0; } 输出:Count of leading zeros before 1 in 16 is 27
注意: __builtin_clz(x)此函数仅接受无符号值
注意:同样,对于长数据类型和长长数据类型,您可以使用__builtin_clzl(x)和__builtin_clzll(x)。 - __builtin_ctz(x):此函数用于计算给定整数的尾随零。注意:ctz =计数尾随零。
示例:从上次出现到第一次出现(置位)时不计零。a = 16 Binary form of 16 is 00000000 00000000 00000000 00010000 Output: ctz = 4
// C program to illustrate __builtin_ctz(x) #include
int main() { int n = 16; printf("Count of zeros from last to first " "occurrence of one is %d", __builtin_ctz(n)); return 0; } 输出:Count of zeros from last to first occurrence of one is 4
注意:同样,对于长数据类型和长长数据类型,您可以使用__builtin_ctzl(x)和__builtin_ctzll(x)。
// C program to illustrate builtin functions of // GCC compiler #include
#include int main() { int num = 4; int clz = 0; int ctz = 0; int pop = 0; int parity = 0; pop = __builtin_popcount(num); printf("Number of one's in %d is %d\n", num, pop); parity = __builtin_parity(num); printf("Parity of %d is %d\n", num, parity); clz = __builtin_clz(num); printf("Number of leading zero's in %d is %d\n", num, clz); // It only works for unsigned values clz = __builtin_clz(-num); printf("Number of leading zero's in %d is %d\n", -num, clz); ctz = __builtin_ctz(num); printf("Number of trailing zero's in %d is %d\n", num, ctz); return 0; } 输出:Number of one's in 4 is 1 Parity of 4 is 1 Number of leading zero's in 4 is 29 Number of leading zero's in -4 is 0 Number of trailing zero's in 4 is 2
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