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/*
* BigInt Encoding/Decoding
* (C) 1999-2010 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#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)
{
SecureVector<byte> binary(n.encoded_size(Binary));
n.binary_encode(&binary[0]);
hex_encode(reinterpret_cast<char*>(output),
&binary[0], binary.size());
}
else if(base == Octal)
{
BigInt copy = n;
const size_t output_size = n.encoded_size(Octal);
for(size_t j = 0; j != output_size; ++j)
{
output[output_size - 1 - j] = Charset::digit2char(copy % 8);
copy /= 8;
}
}
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(remainder.word_at(0));
if(copy.is_zero())
break;
}
}
else
throw Invalid_Argument("Unknown BigInt encoding method");
}
/*
* Encode a BigInt
*/
SecureVector<byte> BigInt::encode(const BigInt& n, Base base)
{
SecureVector<byte> output(n.encoded_size(base));
encode(&output[0], 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
*/
SecureVector<byte> BigInt::encode_1363(const BigInt& n, size_t bytes)
{
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;
SecureVector<byte> output(bytes);
encode(&output[leading_0s], n, Binary);
return output;
}
/*
* Decode a BigInt
*/
BigInt BigInt::decode(const MemoryRegion<byte>& buf, Base base)
{
return BigInt::decode(&buf[0], buf.size(), base);
}
/*
* 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)
{
SecureVector<byte> binary;
if(length % 2)
{
// Handle lack of leading 0
const char buf0_with_leading_0[2] = { '0', buf[0] };
binary = hex_decode(buf0_with_leading_0, 2);
binary += hex_decode(reinterpret_cast<const char*>(&buf[1]),
length - 1,
false);
}
else
binary = hex_decode(reinterpret_cast<const char*>(buf),
length, false);
r.binary_decode(&binary[0], binary.size());
}
else if(base == Decimal || base == Octal)
{
const size_t RADIX = ((base == Decimal) ? 10 : 8);
for(size_t j = 0; j != length; ++j)
{
if(Charset::is_space(buf[j]))
continue;
if(!Charset::is_digit(buf[j]))
throw Invalid_Argument("BigInt::decode: "
"Invalid character in decimal input");
byte x = Charset::char2digit(buf[j]);
if(x >= RADIX)
{
if(RADIX == 10)
throw Invalid_Argument("BigInt: Invalid decimal string");
else
throw Invalid_Argument("BigInt: Invalid octal string");
}
r *= RADIX;
r += x;
}
}
else
throw Invalid_Argument("Unknown BigInt decoding method");
return r;
}
}
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