本文介绍了一系列位操作内置函数，包括查找最右侧1的位置(__builtin_ffs)、计算最高位1前的0数量(__builtin_clz)、计算最低位1后的0数量(__builtin_ctz)、计算1的数量(__builtin_popcount)及计算1的奇偶性(__builtin_parity)等。这些函数适用于不同大小的整数类型。
— Built-in Function: int __builtin_ffs (unsigned int x)
Returns one plus the index of the least significant 1-bit of x, or if x is zero, returns zero.
返回右起第一个‘1’的位置。
— Built-in Function: int __builtin_clz (unsigned int x)
Returns the number of leading 0-bits in x, starting at the most significant bit position. If x is 0, the result is undefined.
返回左起第一个‘1’之前0的个数。
— Built-in Function: int __builtin_ctz (unsigned int x)
Returns the number of trailing 0-bits in x, starting at the least significant bit position. If x is 0, the result is undefined.
返回右起第一个‘1’之后的0的个数。
— Built-in Function: int __builtin_popcount (unsigned int x)
Returns the number of 1-bits in x.
返回‘1’的个数。
— Built-in Function: int __builtin_parity (unsigned int x)
Returns the parity of x, i.e. the number of 1-bits in x modulo 2.
返回‘1’的个数的奇偶性。
— Built-in Function: int __builtin_ffsl (unsigned long)
Similar to __builtin_ffs, except the argument type is unsigned long.
— Built-in Function: int __builtin_clzl (unsigned long)
Similar to __builtin_clz, except the argument type is unsigned long.
— Built-in Function: int __builtin_ctzl (unsigned long)
Similar to __builtin_ctz, except the argument type is unsigned long.
— Built-in Function: int __builtin_popcountl (unsigned long)
Similar to __builtin_popcount, except the argument type is unsigned long.
— Built-in Function: int __builtin_parityl (unsigned long)
Similar to __builtin_parity, except the argument type is unsigned long.
— Built-in Function: int __builtin_ffsll (unsigned long long)
Similar to __builtin_ffs, except the argument type is unsigned long long.
— Built-in Function: int __builtin_clzll (unsigned long long)
Similar to __builtin_clz, except the argument type is unsigned long long.
— Built-in Function: int __builtin_ctzll (unsigned long long)
Similar to __builtin_ctz, except the argument type is unsigned long long.
— Built-in Function: int __builtin_popcountll (unsigned long long)
Similar to __builtin_popcount, except the argument type is unsigned long long.
— Built-in Function: int __builtin_parityll (unsigned long long)
Similar to __builtin_parity, except the argument type is unsigned long long.
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