base91.ts

// Based on http://base91.sourceforge.net/

const lookup: string[] = [];
const revLookup: number[] = [];
const code =
  'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!#$%&()*+,./:;<=>?@[]^_`{|}~"';

for (let i = 0, len = code.length; i < len; ++i) {
  lookup[i] = code[i];
  revLookup[code.charCodeAt(i)] = i;
}
/**
 * Converts given data with base91 encoding
 * @param uint8 input to encode
 */
export function encode(uint8: Uint8Array): string {
  let output = "";
  let queue = 0,
    numbits = 0,
    value = 0;
  for (let i = 0, len = uint8.length; i < len; i++) {
    queue |= uint8[i] << numbits;
    numbits += 8;
    if (numbits > 13) {
      value = queue & 8191;
      if (value > 88) {
        queue >>= 13;
        numbits -= 13;
      } else {
        value = queue & 16383;
        queue >>= 14;
        numbits -= 14;
      }
      output += lookup[value % 91] + lookup[Math.trunc(value / 91)];
    }
  }
  if (numbits > 0) {
    output += lookup[queue % 91];
    if (numbits > 7 || queue > 90) {
      output += lookup[Math.trunc(queue / 91)];
    }
  }
  return output;
}
/**
 * Converts given base91 encoded data back to original Uint8Array
 * @param b91 input to decode
 */
export function decode(b91: string): Uint8Array {
  const output: number[] = [];
  let queue = 0,
    numbits = 0,
    value = -1,
    d = 0;
  for (let i = 0, len = b91.length; i < len; i++) {
    d = revLookup[b91.charCodeAt(i)];
    if (d === undefined) continue;
    if (value == -1) {
      value = d;
    } else {
      value += d * 91;
      queue |= value << numbits;
      numbits += (value & 8191) > 88 ? 13 : 14;
      do {
        output.push(queue);
        queue >>= 8;
        numbits -= 8;
      } while (numbits > 7);
      value = -1;
    }
  }
  if (value != -1) {
    output.push(queue | (value << numbits));
  }
  return new Uint8Array(output);
}