function sumSysv(u8) {
  let crc = 0
  for (let i = 0; i < u8.length; i++) crc += u8[i]
  crc = (crc & 0xffff) + ((crc >> 16) & 0xffff)
  crc = (crc & 0xffff) + ((crc >> 16) & 0xffff)
  return crc & 0xffff
}

function sumBsd(u8) {
  let cksum = 0
  for (let i = 0; i < u8.length; i++) {
    cksum = (cksum >> 1) + ((cksum & 1) << 15)
    cksum = (cksum + u8[i]) & 0xffff
  }
  return cksum
}

async function run(ctx, argv) {
  let bsd = false
  const paths = []
  for (let i = 1; i < argv.length; i++) {
    const a = argv[i]
    if (a === '-h' || a === '--help') {
      ctx.console.log(
        'usage: sum [-r] [FILE]...\n' +
          '  -r  BSD algorithm (default is SysV / CRC16-style sum)'
      )
      ctx.exitCode = 0
      return
    }
    if (a === '-r') bsd = true
    else if (a.startsWith('-') && a !== '-') {
      ctx.console.error('sum: unsupported option ' + a)
      ctx.exitCode = 1
      return
    } else paths.push(a)
  }
  const b4 = ctx.b4a
  function one(name, buf) {
    const u8 = buf instanceof Uint8Array ? buf : new Uint8Array(buf)
    const blocks = Math.ceil(u8.length / 512) || 1
    const v = bsd ? sumBsd(u8) : sumSysv(u8)
    ctx.console.log(v + '\t' + blocks + '\t' + name)
  }
  if (!paths.length || (paths.length === 1 && paths[0] === '-')) {
    one('-', b4.from(bareStdin(ctx)))
    return
  }
  for (const p of paths) {
    if (p === '-') {
      one('-', b4.from(bareStdin(ctx)))
      continue
    }
    const b = await ctx.vfs.readFile(p)
    if (!b) {
      ctx.console.error('sum: ' + p + ': No such file')
      ctx.exitCode = 1
      continue
    }
    one(p, b)
  }
}