Tiny Hiragana encoding

index.js

/*
 * Snippet to encode strings of Hiragana (Japanese alphabet) into a number value.
 *
 * This is written as an example for a Solidity application.
 */

const maxLength = 5;

/*
 * 7 bit for each character.
 */
const bitSize = 7;

// The first element must be an empty string.
const hiraganaList = [
  "",
  ..."あいうえおかきくけこさしすせそたちつてとなにぬねのはひふへほまみむめもやゆよらりるれろわをん".split(""),
  ..."がぎぐげござじずぜぞだぢづでどばびぶべぼぱぴぷぺぽぁぃぅぇぉゃゅょー".split(""),
];

/*
 * 6 bit for each character.
 *
 * This configuration accepts only monographs.
 * If you need to handle diacrics like がぎぐげご and digraphs like きゃきゅきょ,
 * you have to convert them to monographs like かきくけこ or きやきゆきよ in advance.
 *
 * const bitSize = 6;
 * const hiraganaList = [
 *   "",
 *   ..."あいうえおかきくけこさしすせそたちつてとなにぬねのはひふへほまみむめもやゆよらりるれろわをん".split(""),
 * ];
 */

// If bitSize = 7, The size of hiraganaList must be less than 129 including the first empty string.
// If bitSize = 7, The size of hiraganaList must be less than 65 including the first empty string.
console.log(`The size of hiraganaList = ${hiraganaList.length}`)

const mask = (function calculateMask() {
  let mask = 0;

  for (let i = 0; i < bitSize; i++) {
    mask |= 1 << i;
  }

  return mask;
})();

const encode = (word) => {
  // Validate word length. Exception would be better.
  if (word.length > maxLength) { return -1; }

  let encoded = 0;

  word.split("").forEach((c) => {
    encoded <<= bitSize;
    const hiraganaIdx = hiraganaList.indexOf(c);
    encoded |= hiraganaIdx
  })

  return encoded;
};

const decode = (encoded) => {
  if (encoded === -1) { return ""; }

  let word = "";

  for (let i = 0; i < maxLength; i++) {
    const hiraganaIdx = encoded & mask;
    encoded = encoded >>> bitSize;
    word = hiraganaList[hiraganaIdx] + word;
  }

  return word;
}

/* ------- Test code -------- */

const test = (function() {
  let counter = 0;

  return (word) => {
    console.log(`\n======== Test ${counter} ========\n`);
    console.log(`Original word = '${word}'`);

    const enc = encode(word);
    console.log(`Encoded code  = ${enc}`);

    const dec = decode(enc);
    console.log(`Decoded word  = '${dec}'`);

    counter++;
  }
})();

test("あいうえお");
test("おかき");
test("くりえいと");
test("じゃんぷ");
test("なが〜〜〜〜い");