Function Base64Decode

src/StringUtils.cpp:747–776

AString Base64Decode(const AString & a_Base64String)
{
	AString res;
	size_t i, len = a_Base64String.size();
	int o, c;
	res.resize((len * 4) / 3 + 5, 0);  // Approximate the upper bound on the result length
	for (o = 0, i = 0; i < len; i++)
	{
		c = UnBase64(a_Base64String[i]);
		if (c >= 0)
		{
			switch (o & 7)
			{
				case 0:	res[o >> 3] |= (c << 2); break;
				case 6: res[o >> 3] |= (c >> 4); res[(o >> 3) + 1] |= (c << 4); break;
				case 4: res[o >> 3] |= (c >> 2); res[(o >> 3) + 1] |= (c << 6); break;
				case 2: res[o >> 3] |= c; break;
			}
			o += 6;
		}
		if (c == -1)
		{
			// Error while decoding, invalid input. Return as much as we've decoded:
			res.resize(o >> 3);
			return res;
		}
	}
	res.resize(o >> 3);
	return res;
}