jsadvent/lib/BNMath.js

const toIntLookup = new Map(
  Object.entries({
    '0': 0n,
    '1': 1n,
    '2': 2n,
    '3': 3n,
    '4': 4n,
    '5': 5n,
    '6': 6n,
    '7': 7n,
    '8': 8n,
    '9': 9n,
    a: 10n,
    A: 10n,
    b: 11n,
    B: 11n,
    c: 12n,
    C: 12n,
    d: 13n,
    D: 13n,
    e: 14n,
    E: 14n,
    f: 15n,
    F: 15n,
    g: 16n,
    G: 16n,
    h: 17n,
    H: 17n,
    i: 18n,
    I: 18n,
    j: 19n,
    J: 19n,
    k: 20n,
    K: 20n,
    l: 21n,
    L: 21n,
    m: 22n,
    M: 22n,
    n: 23n,
    N: 23n,
    o: 24n,
    O: 24n,
    p: 25n,
    P: 25n,
    q: 26n,
    Q: 26n,
    r: 27n,
    R: 27n,
    s: 28n,
    S: 28n,
    t: 29n,
    T: 29n,
    u: 30n,
    U: 30n,
    v: 31n,
    V: 31n,
    w: 32n,
    W: 32n,
    x: 33n,
    X: 33n,
    y: 34n,
    Y: 34n,
    z: 35n,
    Z: 35n,
  }),
);

const BNMath = (module.exports = {
  min(...nums) {
    if (nums.length === 0) {
      throw new Error('invalid arguments');
    }
    return nums.reduce((a, b) => (a < b ? a : b));
  },
  max(...nums) {
    if (nums.length === 0) {
      throw new Error('invalid arguments');
    }
    return nums.reduce((a, b) => (a > b ? a : b));
  },
  abs(num) {
    if (num < 0n) {
      return num * -1n;
    }
    return num;
  },
  sqrt(num) {
    if (num < 0n) {
      throw new Error('no sqrt of negative');
    }
    if (num <= 1n) {
      return num;
    }

    let x0 = num >> 1n;
    let x1 = (x0 + num / x0) >> 1n;

    while (x1 < x0) {
      x0 = x1;
      x1 = (x0 + num / x0) >> 1n;
    }

    return x0;
  },
  // todo: implement longer string parsing, should be simple-ish to do with
  //   some looping and multiplication
  parseInt(string, radix) {
    if (string.length <= 10) {
      return BigInt(parseInt(string, radix));
    }

    radix = BigInt(radix);

    let result = 0n;
    for (let i = 0; i < string.length; i++) {
      const char = string[string.length - i - 1];
      const num = toIntLookup.get(char);
      if (num >= radix) {
        console.log(char);
        throw new Error('invalid');
      }
      result += num * radix ** i.n;
    }
    return result;
  },
});