multimath/lib/base64decode.js

Core to create fast image math in WebAssembly and JS.

// base64 decode str -> Uint8Array, to load WA modules
//
'use strict';


var BASE64_MAP = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';


module.exports = function base64decode(str) {
  var input = str.replace(/[\r\n=]/g, ''), // remove CR/LF & padding to simplify scan
      max   = input.length;

  var out = new Uint8Array((max * 3) >> 2);

  // Collect by 6*4 bits (3 bytes)

  var bits = 0;
  var ptr  = 0;

  for (var idx = 0; idx < max; idx++) {
    if ((idx % 4 === 0) && idx) {
      out[ptr++] = (bits >> 16) & 0xFF;
      out[ptr++] = (bits >> 8) & 0xFF;
      out[ptr++] = bits & 0xFF;
    }

    bits = (bits << 6) | BASE64_MAP.indexOf(input.charAt(idx));
  }

  // Dump tail

  var tailbits = (max % 4) * 6;

  if (tailbits === 0) {
    out[ptr++] = (bits >> 16) & 0xFF;
    out[ptr++] = (bits >> 8) & 0xFF;
    out[ptr++] = bits & 0xFF;
  } else if (tailbits === 18) {
    out[ptr++] = (bits >> 10) & 0xFF;
    out[ptr++] = (bits >> 2) & 0xFF;
  } else if (tailbits === 12) {
    out[ptr++] = (bits >> 4) & 0xFF;
  }

  return out;
};