IPv4 / IPv6 子网掩码与 CIDR 计算器

// Exact 32-bit Bitwise Subnet Calculator adhering to RFC 4632 & RFC 3021
export interface SubnetInfo {
  cidr: string;
  networkAddress: string;
  broadcastAddress: string;
  subnetMask: string;
  wildcardMask: string;
  firstUsableHost: string;
  lastUsableHost: string;
  totalAddresses: number;
  usableHosts: number;
}

export function calculateSubnet(ipStr: string, prefix: number): SubnetInfo {
  if (prefix < 0 || prefix > 32) throw new Error('Prefix must be between 0 and 32.');

  const octets = ipStr.split('.').map(Number);
  if (octets.length !== 4 || octets.some((o) => isNaN(o) || o < 0 || o > 255)) {
    throw new Error('Invalid IPv4 address format.');
  }

  // Convert IP to 32-bit unsigned int
  const ip32 = ((octets[0] << 24) | (octets[1] << 16) | (octets[2] << 8) | octets[3]) >>> 0;

  // Mask and wildcard
  const mask32 = prefix === 0 ? 0 : (~0 << (32 - prefix)) >>> 0;
  const wildcard32 = (~mask32) >>> 0;

  // Network and broadcast boundaries
  const network32 = (ip32 & mask32) >>> 0;
  const broadcast32 = (network32 | wildcard32) >>> 0;

  const intToIp = (val: number) =>
    [(val >>> 24) & 255, (val >>> 16) & 255, (val >>> 8) & 255, val & 255].join('.');

  const total = Math.pow(2, 32 - prefix);
  let usable = 0;
  let firstHost = '';
  let lastHost = '';

  if (prefix === 32) {
    usable = 1;
    firstHost = intToIp(network32);
    lastHost = intToIp(network32);
  } else if (prefix === 31) {
    // RFC 3021 point-to-point links
    usable = 2;
    firstHost = intToIp(network32);
    lastHost = intToIp(broadcast32);
  } else {
    usable = Math.max(0, total - 2);
    firstHost = intToIp(network32 + 1);
    lastHost = intToIp(broadcast32 - 1);
  }

  return {
    cidr: `${intToIp(network32)}/${prefix}`,
    networkAddress: intToIp(network32),
    broadcastAddress: intToIp(broadcast32),
    subnetMask: intToIp(mask32),
    wildcardMask: intToIp(wildcard32),
    firstUsableHost: firstHost,
    lastUsableHost: lastHost,
    totalAddresses: total,
    usableHosts: usable
  };
}