base64.cpp

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#include "joedb/ui/base64.h"
 
#include <stdint.h>
 
namespace joedb
{
 static char const base64_codes[] =
  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
 ////////////////////////////////////////////////////////////////////////////
 std::string base64_encode(const std::string &input)
 ////////////////////////////////////////////////////////////////////////////
 {
  const size_t N = input.size() / 3;
  const size_t remainder = input.size() % 3;
 
  std::string result;
  result.resize(4 * (N + static_cast<size_t>(remainder != 0)));
 
  for (size_t i = 0; i < N; i++)
  {
   const uint32_t word = (uint32_t(uint8_t(input[3 * i + 0])) << 16) |
                         (uint32_t(uint8_t(input[3 * i + 1])) <<  8) |
                         (uint32_t(uint8_t(input[3 * i + 2]))      );
   result[4 * i + 0] = base64_codes[(word >> 18)       ];
   result[4 * i + 1] = base64_codes[(word >> 12) & 0x3f];
   result[4 * i + 2] = base64_codes[(word >>  6) & 0x3f];
   result[4 * i + 3] = base64_codes[(word      ) & 0x3f];
  }
 
  if (remainder == 2)
  {
   const int32_t word = (uint8_t(input[3 * N + 0]) << 10) |
                        (uint8_t(input[3 * N + 1]) <<  2);
   result[4 * N + 0] = base64_codes[(word >> 12)       ];
   result[4 * N + 1] = base64_codes[(word >>  6) & 0x3f];
   result[4 * N + 2] = base64_codes[(word      ) & 0x3f];
   result[4 * N + 3] = '=';
  }
  else if (remainder == 1)
  {
   const int32_t word = (uint8_t(input[3 * N + 0]) << 4);
   result[4 * N + 0] = base64_codes[(word >>  6)       ];
   result[4 * N + 1] = base64_codes[(word      ) & 0x3f];
   result[4 * N + 2] = '=';
   result[4 * N + 3] = '=';
  }
 
  return result;
 }
}