bops/typedarray/from.js

buffer operations

module.exports = from

var base64 = require('base64-js')

var decoders = {
    hex: from_hex
  , utf8: from_utf
  , base64: from_base64
}

function from(source, encoding) {
  if(Array.isArray(source)) {
    return new Uint8Array(source)
  }

  return decoders[encoding || 'utf8'](source)
}

function from_hex(str) {
  var size = str.length / 2
    , buf = new Uint8Array(size)
    , character = ''

  for(var i = 0, len = str.length; i < len; ++i) {
    character += str.charAt(i)

    if(i > 0 && (i % 2) === 1) {
      buf[i>>>1] = parseInt(character, 16)
      character = '' 
    }
  }

  return buf 
}

function from_utf(str) {
  var arr = []
    , code

  for(var i = 0, len = str.length; i < len; ++i) {
    code = fixed_cca(str, i)

    if(code === false) {
      continue
    }

    if(code < 0x80) {
      arr[arr.length] = code

      continue
    }

    codepoint_to_bytes(arr, code)
  }

  return new Uint8Array(arr)
}

function codepoint_to_bytes(arr, code) {
  // find MSB, use that to determine byte count
  var copy_code = code
    , bit_count = 0
    , byte_count
    , prefix
    , _byte
    , pos

  do {
    ++bit_count
  } while(copy_code >>>= 1)

  byte_count = Math.ceil((bit_count - 1) / 5) | 0
  prefix = [0, 0, 0xc0, 0xe0, 0xf0, 0xf8, 0xfc][byte_count]
  pos = [0, 0, 3, 4, 5, 6, 7][byte_count]

  _byte |= prefix

  bit_count = (7 - pos) + 6 * (byte_count - 1)

  while(bit_count) {
    _byte |= +!!(code & (1 << bit_count)) << (7 - pos)
    ++pos

    if(pos % 8 === 0) {
      arr[arr.length] = _byte
      _byte = 0x80
      pos = 2
    }

    --bit_count
  }

  if(pos) {
    _byte |= +!!(code & 1) << (7 - pos)
    arr[arr.length] = _byte
  }
}

function pad(str) {
  while(str.length < 8) {
    str = '0' + str
  }

  return str
}

function fixed_cca(str, idx) {
  idx = idx || 0

  var code = str.charCodeAt(idx)
    , lo
    , hi

  if(0xD800 <= code && code <= 0xDBFF) {
    lo = str.charCodeAt(idx + 1)
    hi = code

    if(isNaN(lo)) {
      throw new Error('High surrogate not followed by low surrogate')
    }

    return ((hi - 0xD800) * 0x400) + (lo - 0xDC00) + 0x10000
  }

  if(0xDC00 <= code && code <= 0xDFFF) {
    return false
  }

  return code
}

function from_base64(str) {
  return new Uint8Array(base64.toByteArray(str)) 
}