assemblyscript/bin/util/utf8.js

// see: https://github.com/dcodeIO/protobuf.js/tree/master/lib/utf8

exports.length = function utf8_length(string) {
  var len = 0,
    c = 0;
  for (var i = 0; i < string.length; ++i) {
    c = string.charCodeAt(i);
    if (c < 128) {
      len += 1;
    } else if (c < 2048) {
      len += 2;
    } else if ((c & 0xFC00) === 0xD800 && (string.charCodeAt(i + 1) & 0xFC00) === 0xDC00) {
      ++i;
      len += 4;
    } else {
      len += 3;
    }
  }
  return len;
};

exports.read = function utf8_read(buffer, start, end) {
  var len = end - start;
  if (len < 1)
    return "";
  var parts = null,
    chunk = [],
    i = 0, t;
  while (start < end) {
    t = buffer[start++];
    if (t < 128) {
      chunk[i++] = t;
    } else if (t > 191 && t < 224) {
      chunk[i++] = (t & 31) << 6 | buffer[start++] & 63;
    } else if (t > 239 && t < 365) {
      t = ((t & 7) << 18 | (buffer[start++] & 63) << 12 | (buffer[start++] & 63) << 6 | buffer[start++] & 63) - 0x10000;
      chunk[i++] = 0xD800 + (t >> 10);
      chunk[i++] = 0xDC00 + (t & 1023);
    } else {
      chunk[i++] = (t & 15) << 12 | (buffer[start++] & 63) << 6 | buffer[start++] & 63;
    }
    if (i > 8191) {
      (parts || (parts = [])).push(String.fromCharCode.apply(String, chunk));
      i = 0;
    }
  }
  if (parts) {
    if (i) parts.push(String.fromCharCode.apply(String, chunk.slice(0, i)));
    return parts.join("");
  }
  return String.fromCharCode.apply(String, chunk.slice(0, i));
};

exports.write = function utf8_write(string, buffer, offset) {
  var start = offset,
      c1, c2;
  for (var i = 0; i < string.length; ++i) {
    c1 = string.charCodeAt(i);
    if (c1 < 128) {
      buffer[offset++] = c1;
    } else if (c1 < 2048) {
      buffer[offset++] = c1 >> 6 | 192;
      buffer[offset++] = c1 & 63 | 128;
    } else if ((c1 & 0xFC00) === 0xD800 && ((c2 = string.charCodeAt(i + 1)) & 0xFC00) === 0xDC00) {
      c1 = 0x10000 + ((c1 & 0x03FF) << 10) + (c2 & 0x03FF);
      ++i;
      buffer[offset++] = c1 >> 18 | 240;
      buffer[offset++] = c1 >> 12 & 63 | 128;
      buffer[offset++] = c1 >> 6 & 63 | 128;
      buffer[offset++] = c1 & 63 | 128;
    } else {
      buffer[offset++] = c1 >> 12 | 224;
      buffer[offset++] = c1 >> 6 & 63 | 128;
      buffer[offset++] = c1 & 63 | 128;
    }
  }
  return offset - start;
};