位运算及用位运算实现权限控制

请自行补习位运算相关知识

位运算

    // 按位与 & ，相同位均为1则1, 否则为0
    0b1100 & 0b1001 // 0b1000

    // 按位或 | ，相同位只要有一个为1即为1
    0b1100 | 0b1001 // 0b1101

    // 按位异或 ^ ，相同位不同则为1, 否则为0
    0b1100 ^ 0b1001 // 0b0101

    // 按位取反 ~
    ~0b1100 // -0b1101

    // 左移 <<
    1 << 10 // 1024

    // 带符号右移 >>
    5 >> 1 // 2
    -4 >> 1 // -2

    // 无符号右移 >>> (部分语言支持)
    -4 >>> 1 // 2147483646

位运算示例

    // y 为下标, 从0开始
    // 将 x 的指定位 y 置1
    x |= (1<<y)

    // 将 x 的指定位 y 置0
    x &= ~(1<<y)

    // 将 x 的指定位 y 取反
    x ^= (1<<y)

    // 取 x 的指定位 y 的值
    x >> y&1

权限控制

// 可以复制到浏览器控制台测试输出结果
const P_0 = 0;
const P_1 = 1 << 0;
const P_2 = 1 << 1;
const P_3 = 1 << 2;
const P_4 = 1 << 3;
const P_5 = 1 << 4;
const P_6 = 1 << 5;
const P_7 = 1 << 6;


console.log('权限表：');
console.log('权限1: P_0 :', P_0.toString(2), P_0);
console.log('权限2: P_1 :', P_1.toString(2), P_1);
console.log('权限3: P_2 :', P_2.toString(2), P_2);
console.log('权限4: P_3 :', P_3.toString(2), P_3);
console.log('权限5: P_4 :', P_4.toString(2), P_4);
console.log('权限6: P_5 :', P_5.toString(2), P_5);
console.log('权限7: P_6 :', P_6.toString(2), P_6);
console.log('权限8: P_7 :', P_7.toString(2), P_7);

console.log('\n赋值对应权限：');
let pAllowed = P_0;
console.log('pAllowed 初始值:', pAllowed.toString(2));
console.log('pAllowed |= P_1 :', (pAllowed |= P_1).toString(2), pAllowed);
console.log('pAllowed |= P_2 :', (pAllowed |= P_2).toString(2), pAllowed);
console.log('pAllowed |= P_3 :', (pAllowed |= P_3).toString(2), pAllowed);
console.log('pAllowed |= P_4 :', (pAllowed |= P_4).toString(2), pAllowed);
console.log('pAllowed |= P_5 :', (pAllowed |= P_5).toString(2), pAllowed);
console.log('pAllowed |= P_6 :', (pAllowed |= P_6).toString(2), pAllowed);
console.log('pAllowed |= P_7 :', (pAllowed |= P_7).toString(2), pAllowed);
console.log('pAllowed 对应位赋值权限后:', pAllowed.toString(2), pAllowed);

console.log('\n取消对应权限：');
console.log('pAllowed &= ~P_1 :', (pAllowed &= ~P_1).toString(2), pAllowed);
console.log('pAllowed &= ~P_2 :', (pAllowed &= ~P_2).toString(2), pAllowed);
console.log('pAllowed &= ~P_3 :', (pAllowed &= ~P_3).toString(2), pAllowed);
console.log('pAllowed &= ~P_4 :', (pAllowed &= ~P_4).toString(2), pAllowed);
console.log('pAllowed &= ~P_5 :', (pAllowed &= ~P_5).toString(2), pAllowed);
console.log('pAllowed &= ~P_6 :', (pAllowed &= ~P_6).toString(2), pAllowed);
console.log('pAllowed &= ~P_7 :', (pAllowed &= ~P_7).toString(2), pAllowed);
console.log('pAllowed 对应位取消权限后:', pAllowed.toString(2), pAllowed);

console.log('\n同时赋值多个权限：');
console.log('pAllowed |= (P_1 | P_2 | P_3 | P_4 | P_5 | P_6 | P_7) :',
    (pAllowed |= (P_1 | P_2 | P_3 | P_4 | P_5 | P_6 | P_7)).toString(2), pAllowed);

console.log('\n同时取消多个权限：');
console.log('pAllowed &= ~(P_1 | P_2 | P_3 | P_4 | P_5 | P_6 | P_7) :',
    (pAllowed &= ~(P_1 | P_2 | P_3 | P_4 | P_5 | P_6 | P_7)).toString(2), pAllowed);

最后编辑于：2018.10.30 16:53:06