ipv6

ipv6.js

function getBitsAfter33(ipv6) {
  function hexTo2Bits(v, bitLength = 4) {
    if(v >= 10) {
      v = "ABCDEF"[v - 10]
    }
    return (new Array(bitLength).fill("0").join("") + parseInt(v, 16).toString(2)).slice(-bitLength);
  }
  function bit2toHex(num) {
    var p = num.split("").reverse().map((v, i) => Math.pow(2, i) * parseInt(v)).reduce((memo, v) => memo + v, 0);
    if(p < 10) {
      return "" + p
    } else {
      return "ABCDEF"[p - 10]
    }
  }
  
  var [body, tail] = ipv6.split("::/");
  const fixedBit = parseInt(tail) - 32;
  const variableBit = 4 - fixedBit;
  
  if(fixedBit < 0 || fixedBit > 4) {
    throw new Error("大きすぎ");
  }
  if(fixedBit == 0) {
    return;
  }
  var seg = body.split(":")[2];
  var value = "0000";
  if(seg) {
    value = hexTo2Bits(seg[0]);
  }
  const fixed = value.slice(0, fixedBit);
  var result = "";
  for(let i = 0; i < Math.pow(2, variableBit); i++) {
    var p = fixed + hexTo2Bits(i, variableBit);
    // console.log(p, bit2toHex(p));
    result += bit2toHex(p);
    // console.log(i, fixed + hexTo2Bits(i, variableBit));
  }
  return `[${result}]`;
}

function convert(ipv6) {
  return [...ipv6.split(":").slice(0, 2), getBitsAfter33(ipv6)].filter(v =>v).join(":")
}


console.log(convert("0000:0000:8000::/32"))