Bitwise in JavaScript

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tinyhuang Jun 04, 2018

There are only two numbers in the world: 0 and 1

先写一个凑齐 32 位的方法吧

因为 log 打印不出来那么多的 0,位运算中的左移啥的看不清楚

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//Zero Fill
const binary = (decimal = 0) => {
  if (decimal.toString(2) >= 0) {
    let bin = decimal.toString(2);
    if (bin.length < 32) {
      let arr = bin.split(' ');
      let remainStr = `0`.repeat(32 - bin.length);
      arr.unshift(remainStr);
      return arr.join('');
    }
  } else {
    let transformBin = (~decimal).toString(2);
    if (transformBin.length < 32) {
      let arr = transformBin.split(' ');
      let remainStr = `0`.repeat(32 - transformBin.length);
      arr.unshift(remainStr);
      let newResult = arr.join('').split('');
      var brr = [];
      for (var i in newResult) {
        if (newResult[i] == '1') {
          brr[i] = i;
        }
        if (newResult[i] == '0') {
          newResult[i] = '1';
        }
      }
      var crr = brr.filter(x => typeof x == 'string').map(y => Number(y));
      for (var c in crr) {
        newResult[crr[c]] = '0';
      }
      return newResult.join('');
    }
  }
};

Bitwise NOT(~)

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const a = 25;
const b = ~a;
const c = -a - 1;

console.time(`b`);
console.log(b); //-26
console.timeEnd(`b`); //2.306ms

console.time(`c`);
console.log(c);
console.timeEnd(`c`); //2.449ms

位运算更接近底层吧,速度快那么一丢丢

Bitwise AND(&)

两位都是 1 => return 1

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const d = 25;
const e = 3;
console.log(binary(25));
00000000000000000000000000011001;
console.log(binary(3));
00000000000000000000000000000011;
console.log(binary(d & e));
00000000000000000000000000000001;
console.log(d & e); //1

Bitwise OR(|)

任一位是 1 => return 1

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console.log(binary(d));
00000000000000000000000000011001;
console.log(binary(e));
00000000000000000000000000000011;
console.log(binary(d | e));
00000000000000000000000000011011;
console.log(d | e); //27

Bitwise XOR

只有一位是 1 => return 1

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console.log(binary(d));
00000000000000000000000000011001;
console.log(binary(e));
00000000000000000000000000000011;
console.log(binary(d ^ e));
00000000000000000000000000011010;
console.log(d ^ e); //26

Left Shift (<<)

所有位左移指定的位数

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const f = 2;
console.log(binary(f));
00000000000000000000000000000010;
console.log(binary(f << 9));
00000000000000000000010000000000;

Signed Right Shift (>>)

符号位保留,其他位指定右移的位数

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console.log(binary(2));
00000000000000000000000000000010;
console.log(binary(64));
00000000000000000000000001000000;
console.log(binary(64 >> 5));
00000000000000000000000000000010;

Unsigned Right Shift (>>>)

所有的位都指定右移的位数

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console.log(binary(-64));
11111111111111111111111111000000;
console.log(binary(-64 >>> 5));
00000111111111111111111111111110;