src/Base64.cpp

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#include "Base64.h"

namespace nt {

// aaaack but it's fast and const should make it shared text page.
static const unsigned char pr2six[256] =
{
    // ASCII table
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 62, 64, 64, 64, 63,
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 64, 64, 64, 64, 64, 64,
    64,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 64, 64, 64, 64, 64,
    64, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64
};

std::size_t Base64Decode(llvm::StringRef encoded, std::string* plain) {
  const unsigned char *end = encoded.bytes_begin();
  while (pr2six[*end] <= 63 && end != encoded.bytes_end()) ++end;
  std::size_t nprbytes = end - encoded.bytes_begin();

  plain->clear();
  if (nprbytes == 0)
    return 0;
  plain->reserve(((nprbytes + 3) / 4) * 3);

  const unsigned char *cur = encoded.bytes_begin();

  while (nprbytes > 4) {
    (*plain) += (pr2six[cur[0]] << 2 | pr2six[cur[1]] >> 4);
    (*plain) += (pr2six[cur[1]] << 4 | pr2six[cur[2]] >> 2);
    (*plain) += (pr2six[cur[2]] << 6 | pr2six[cur[3]]);
    cur += 4;
    nprbytes -= 4;
  }

  // Note: (nprbytes == 1) would be an error, so just ignore that case
  if (nprbytes > 1) (*plain) += (pr2six[cur[0]] << 2 | pr2six[cur[1]] >> 4);
  if (nprbytes > 2) (*plain) += (pr2six[cur[1]] << 4 | pr2six[cur[2]] >> 2);
  if (nprbytes > 3) (*plain) += (pr2six[cur[2]] << 6 | pr2six[cur[3]]);

  return (end - encoded.bytes_begin()) + ((4 - nprbytes) & 3);
}

static const char basis_64[] =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

void Base64Encode(llvm::StringRef plain, std::string* encoded) {
  encoded->clear();
  if (plain.empty())
    return;
  std::size_t len = plain.size();
  encoded->reserve(((len + 2) / 3 * 4) + 1);

  std::size_t i;
  for (i = 0; (i + 2) < len; i += 3) {
    (*encoded) += basis_64[(plain[i] >> 2) & 0x3F];
    (*encoded) +=
        basis_64[((plain[i] & 0x3) << 4) | ((int)(plain[i + 1] & 0xF0) >> 4)];
    (*encoded) += basis_64[((plain[i + 1] & 0xF) << 2) |
                           ((int)(plain[i + 2] & 0xC0) >> 6)];
    (*encoded) += basis_64[plain[i + 2] & 0x3F];
  }
  if (i < len) {
    (*encoded) += basis_64[(plain[i] >> 2) & 0x3F];
    if (i == (len - 1)) {
      (*encoded) += basis_64[((plain[i] & 0x3) << 4)];
      (*encoded) += '=';
    } else {
      (*encoded) +=
          basis_64[((plain[i] & 0x3) << 4) | ((int)(plain[i + 1] & 0xF0) >> 4)];
      (*encoded) += basis_64[((plain[i + 1] & 0xF) << 2)];
    }
    (*encoded) += '=';
  }
}

}  // namespace nt