/*
* BigInt Encoding/Decoding
* (C) 1999-2010,2012 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/bigint.h>
#include <botan/divide.h>
#include <botan/charset.h>
#include <botan/hex.h>

namespace Botan {

/*
* Encode a BigInt
*/
void BigInt::encode(byte output[], const BigInt& n, Base base)
   {
   if(base == Binary)
      {
      n.binary_encode(output);
      }
   else if(base == Hexadecimal)
      {
      secure_vector<byte> binary(n.encoded_size(Binary));
      n.binary_encode(binary.data());

      hex_encode(reinterpret_cast<char*>(output),
                 binary.data(), binary.size());
      }
   else if(base == Decimal)
      {
      BigInt copy = n;
      BigInt remainder;
      copy.set_sign(Positive);
      const size_t output_size = n.encoded_size(Decimal);
      for(size_t j = 0; j != output_size; ++j)
         {
         divide(copy, 10, copy, remainder);
         output[output_size - 1 - j] =
            Charset::digit2char(static_cast<byte>(remainder.word_at(0)));
         if(copy.is_zero())
            break;
         }
      }
   else
      throw Invalid_Argument("Unknown BigInt encoding method");
   }

/*
* Encode a BigInt
*/
std::vector<byte> BigInt::encode(const BigInt& n, Base base)
   {
   std::vector<byte> output(n.encoded_size(base));
   encode(output.data(), n, base);
   if(base != Binary)
      for(size_t j = 0; j != output.size(); ++j)
         if(output[j] == 0)
            output[j] = '0';
   return output;
   }

/*
* Encode a BigInt
*/
secure_vector<byte> BigInt::encode_locked(const BigInt& n, Base base)
   {
   secure_vector<byte> output(n.encoded_size(base));
   encode(output.data(), n, base);
   if(base != Binary)
      for(size_t j = 0; j != output.size(); ++j)
         if(output[j] == 0)
            output[j] = '0';
   return output;
   }

/*
* Encode a BigInt, with leading 0s if needed
*/
secure_vector<byte> BigInt::encode_1363(const BigInt& n, size_t bytes)
   {
   secure_vector<byte> output(bytes);
   BigInt::encode_1363(output.data(), output.size(), n);
   return output;
   }

//static
void BigInt::encode_1363(byte output[], size_t bytes, const BigInt& n)
   {
   const size_t n_bytes = n.bytes();
   if(n_bytes > bytes)
      throw Encoding_Error("encode_1363: n is too large to encode properly");

   const size_t leading_0s = bytes - n_bytes;
   encode(&output[leading_0s], n, Binary);
   }

/*
* Encode two BigInt, with leading 0s if needed, and concatenate
*/
secure_vector<byte> BigInt::encode_fixed_length_int_pair(const BigInt& n1, const BigInt& n2, size_t bytes)
   {
   secure_vector<byte> output(2 * bytes);
   BigInt::encode_1363(output.data(), bytes, n1);
   BigInt::encode_1363(output.data() + bytes, bytes, n2);
   return output;
   }

/*
* Decode a BigInt
*/
BigInt BigInt::decode(const byte buf[], size_t length, Base base)
   {
   BigInt r;
   if(base == Binary)
      r.binary_decode(buf, length);
   else if(base == Hexadecimal)
      {
      secure_vector<byte> binary;

      if(length % 2)
         {
         // Handle lack of leading 0
         const char buf0_with_leading_0[2] =
            { '0', static_cast<char>(buf[0]) };

         binary = hex_decode_locked(buf0_with_leading_0, 2);

         binary += hex_decode_locked(reinterpret_cast<const char*>(&buf[1]),
                                     length - 1,
                                     false);
         }
      else
         binary = hex_decode_locked(reinterpret_cast<const char*>(buf),
                                    length, false);

      r.binary_decode(binary.data(), binary.size());
      }
   else if(base == Decimal)
      {
      for(size_t i = 0; i != length; ++i)
         {
         if(Charset::is_space(buf[i]))
            continue;

         if(!Charset::is_digit(buf[i]))
            throw Invalid_Argument("BigInt::decode: "
                                   "Invalid character in decimal input");

         const byte x = Charset::char2digit(buf[i]);

         if(x >= 10)
            throw Invalid_Argument("BigInt: Invalid decimal string");

         r *= 10;
         r += x;
         }
      }
   else
      throw Invalid_Argument("Unknown BigInt decoding method");
   return r;
   }

}