@thi.ng/base-n/decode.js

Arbitrary base-n conversions w/ presets for base8/16/32/36/58/62/64/83/85, support for bigints and encoding/decoding of byte arrays

class BaseNDecoder {
  constructor(base) {
    this.base = base;
    this.N = base.length;
    this.index = [...base].reduce(
      (acc, x, i) => (acc[x] = i, acc),
      {}
    );
  }
  N;
  index;
  decode(x) {
    const { index, N } = this;
    let res = 0;
    for (let n = x.length - 1, i = 0; i <= n; i++) {
      res += index[x[i]] * N ** (n - i);
    }
    return res;
  }
  decodeBigInt(x) {
    const { index, N } = this;
    const NN = BigInt(N);
    let res = 0n;
    for (let n = x.length - 1, i = 0; i <= n; i++) {
      res += BigInt(index[x[i]]) * NN ** BigInt(n - i);
    }
    return res;
  }
  decodeBytes(x, buf) {
    let y = this.decodeBigInt(x);
    for (let i = buf.length; i-- > 0; ) {
      buf[i] = Number(y & 255n);
      y >>= 8n;
    }
    return buf;
  }
  validate(x) {
    return new RegExp(`^[${this.base}]+$`).test(x);
  }
}
export {
  BaseNDecoder
};