位运算

[district10]

#include <stdio.h>

#define PRINT(x) printf("hex: 0x%08x, dec: %12d, str: \"%s\"\n", x, x, #x)

int main()
{
    puts( "全 0 & 全 1" );
    PRINT( 0 );
    PRINT( -1 );

    puts( "\n全 1 的左右 shift" );
    PRINT( -1>>1 );
    PRINT( -1<<1 );

    puts( "\n减法优先级更高" );
    PRINT( 1<<31-1 );
    PRINT( 1<<30 );

    puts( "\n怎么得到 int 的最大正数" );
    PRINT( 1<<31 );
    PRINT( (1<<31)-1 );
    PRINT( ((unsigned int)1<<31)-1 );
    PRINT( ((unsigned int)-1)>>1 );
    PRINT( -1>>1 );
    PRINT( 0x7FFFFFFF );
}

编译：gcc test.c -o test，

运行：./test

结果：

全 0 & 全 1
hex: 0x00000000, dec:            0, str: "0"
hex: 0xffffffff, dec:           -1, str: "-1"

全 1 的左右 shift
hex: 0xffffffff, dec:           -1, str: "-1>>1"
hex: 0xfffffffe, dec:           -2, str: "-1<<1"

减法优先级更高
hex: 0x40000000, dec:   1073741824, str: "1<<31-1"
hex: 0x40000000, dec:   1073741824, str: "1<<30"

怎么得到 int 的最大正数
hex: 0x80000000, dec:  -2147483648, str: "1<<31"
hex: 0x7fffffff, dec:   2147483647, str: "(1<<31)-1"
hex: 0x7fffffff, dec:   2147483647, str: "((unsigned int)1<<31)-1"
hex: 0x7fffffff, dec:   2147483647, str: "((unsigned int)-1)>>1"
hex: 0xffffffff, dec:           -1, str: "-1>>1"
hex: 0x7fffffff, dec:   2147483647, str: "0x7FFFFFFF"