通过位运算把一个数的最高位设成所有位怎么做？

Question

copyMSB - set all bits of result to most significant bit of x.

    Examples: copyMSB(0x80000000) = 0xFFFFFFFF
                                      copyMSB(0x70000000) = 0x00000000
      Legal ops: ! ~ & ^ | + << >>
      Max ops: 5

不能用if-else。

Answer 1

 unsigned int copyMSB(unsigned int x)
{
    return x >> 31 << 31;
}

int main()
{
    printf("%d\n", copyMSB(0x80000000));
    printf("%d\n", copyMSB(0x70000000));
}