codec.cpp

std::string EncodeBase64(std::string_view v) {
  size_t sz = v.size();
  size_t padding = sz % 3;
  if (padding) {
    padding = 3 - padding;
  }
  sz += padding;
  ASSERT_DEBUG(sz % 3 == 0);
  std::string out(sz * 4 / 3, 0);

  size_t p = 0;
  for (size_t i = 0; i < sz; i += 3) {
    uint8_t b = v[i] >> 2;
    ASSERT_DEBUG(b < 64);
    out[p++] = B64_TABLE[b];

    b = ((v[i] & 0x3) << 4) + (v[i + 1] >> 4);
    ASSERT_DEBUG(b < 64);
    out[p++] = B64_TABLE[b];

    b = ((v[i + 1] & 0xf) << 2) + (v[i + 2] >> 6);
    ASSERT_DEBUG(b < 64);
    out[p++] = B64_TABLE[b];

    b = v[i + 2] & 0x3f;
    ASSERT_DEBUG(b < 64);
    out[p++] = B64_TABLE[b];
  }

  // add padding bytes
  for (size_t i = 0; i < padding; i++) {
    out[p++] = '=';
  }

  ASSERT_DEBUG(p == out.size());
  return out;
}