path: root/src/lib/math/bigint/bigint.cpp

/*
* BigInt Base
* (C) 1999-2011,2012,2014 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/bigint.h>
#include <botan/internal/mp_core.h>
#include <botan/internal/rounding.h>
#include <botan/internal/bit_ops.h>
#include <botan/internal/ct_utils.h>

namespace Botan {

BigInt::BigInt(const word words[], size_t length)
   {
   m_reg.assign(words, words + length);
   }

/*
* Construct a BigInt from a regular number
*/
BigInt::BigInt(uint64_t n)
   {
   if(n == 0)
      return;

   const size_t limbs_needed = sizeof(uint64_t) / sizeof(word);

   m_reg.resize(limbs_needed);
   for(size_t i = 0; i != limbs_needed; ++i)
      m_reg[i] = ((n >> (i*MP_WORD_BITS)) & MP_WORD_MASK);
   }

/*
* Construct a BigInt of the specified size
*/
BigInt::BigInt(Sign s, size_t size)
   {
   m_reg.resize(round_up(size, 8));
   m_signedness = s;
   }

/*
* Copy constructor
*/
BigInt::BigInt(const BigInt& other)
   {
   m_reg = other.m_reg;
   m_signedness = other.m_signedness;
   }

/*
* Construct a BigInt from a string
*/
BigInt::BigInt(const std::string& str)
   {
   Base base = Decimal;
   size_t markers = 0;
   bool negative = false;

   if(str.length() > 0 && str[0] == '-')
      {
      markers += 1;
      negative = true;
      }

   if(str.length() > markers + 2 && str[markers    ] == '0' &&
                                    str[markers + 1] == 'x')
      {
      markers += 2;
      base = Hexadecimal;
      }

   *this = decode(cast_char_ptr_to_uint8(str.data()) + markers,
                  str.length() - markers, base);

   if(negative) set_sign(Negative);
   else         set_sign(Positive);
   }

/*
* Construct a BigInt from an encoded BigInt
*/
BigInt::BigInt(const uint8_t input[], size_t length, Base base)
   {
   *this = decode(input, length, base);
   }

/*
* Construct a BigInt from an encoded BigInt
*/
BigInt::BigInt(RandomNumberGenerator& rng, size_t bits, bool set_high_bit)
   {
   randomize(rng, bits, set_high_bit);
   }

/*
* Comparison Function
*/
int32_t BigInt::cmp(const BigInt& other, bool check_signs) const
   {
   if(check_signs)
      {
      if(other.is_positive() && this->is_negative())
         return -1;

      if(other.is_negative() && this->is_positive())
         return 1;

      if(other.is_negative() && this->is_negative())
         return (-bigint_cmp(this->data(), this->sig_words(),
                             other.data(), other.sig_words()));
      }

   return bigint_cmp(this->data(), this->sig_words(),
                     other.data(), other.sig_words());
   }

/*
* Return bits {offset...offset+length}
*/
uint32_t BigInt::get_substring(size_t offset, size_t length) const
   {
   if(length > 32)
      throw Invalid_Argument("BigInt::get_substring: Substring size " + std::to_string(length) + " too big");

   uint64_t piece = 0;
   for(size_t i = 0; i != 8; ++i)
      {
      const uint8_t part = byte_at((offset / 8) + (7-i));
      piece = (piece << 8) | part;
      }

   const uint64_t mask = (static_cast<uint64_t>(1) << length) - 1;
   const size_t shift = (offset % 8);

   return static_cast<uint32_t>((piece >> shift) & mask);
   }

/*
* Convert this number to a uint32_t, if possible
*/
uint32_t BigInt::to_u32bit() const
   {
   if(is_negative())
      throw Encoding_Error("BigInt::to_u32bit: Number is negative");
   if(bits() > 32)
      throw Encoding_Error("BigInt::to_u32bit: Number is too big to convert");

   uint32_t out = 0;
   for(size_t i = 0; i != 4; ++i)
      out = (out << 8) | byte_at(3-i);
   return out;
   }

/*
* Set bit number n
*/
void BigInt::set_bit(size_t n)
   {
   const size_t which = n / MP_WORD_BITS;
   const word mask = static_cast<word>(1) << (n % MP_WORD_BITS);
   if(which >= size()) grow_to(which + 1);
   m_reg[which] |= mask;
   }

/*
* Clear bit number n
*/
void BigInt::clear_bit(size_t n)
   {
   const size_t which = n / MP_WORD_BITS;
   const word mask = static_cast<word>(1) << (n % MP_WORD_BITS);
   if(which < size())
      m_reg[which] &= ~mask;
   }

size_t BigInt::bytes() const
   {
   return round_up(bits(), 8) / 8;
   }

/*
* Count how many bits are being used
*/
size_t BigInt::bits() const
   {
   const size_t words = sig_words();

   if(words == 0)
      return 0;

   const size_t full_words = words - 1;
   return (full_words * MP_WORD_BITS + high_bit(word_at(full_words)));
   }

/*
* Calcluate the size in a certain base
*/
size_t BigInt::encoded_size(Base base) const
   {
   static const double LOG_2_BASE_10 = 0.30102999566;

   if(base == Binary)
      return bytes();
   else if(base == Hexadecimal)
      return 2*bytes();
   else if(base == Decimal)
      return static_cast<size_t>((bits() * LOG_2_BASE_10) + 1);
   else
      throw Invalid_Argument("Unknown base for BigInt encoding");
   }

/*
* Return the negation of this number
*/
BigInt BigInt::operator-() const
   {
   BigInt x = (*this);
   x.flip_sign();
   return x;
   }

void BigInt::reduce_below(const BigInt& p, secure_vector<word>& ws)
   {
   if(p.is_negative())
      throw Invalid_Argument("BigInt::reduce_below mod must be positive");

   const size_t p_words = p.sig_words();

   if(size() < p_words + 1)
      grow_to(p_words + 1);

   if(ws.size() < p_words + 1)
      ws.resize(p_words + 1);

   clear_mem(ws.data(), ws.size());

   for(;;)
      {
      word borrow = bigint_sub3(ws.data(), data(), p_words + 1, p.data(), p_words);

      if(borrow)
         break;

      m_reg.swap(ws);
      }
   }

/*
* Return the absolute value of this number
*/
BigInt BigInt::abs() const
   {
   BigInt x = (*this);
   x.set_sign(Positive);
   return x;
   }

void BigInt::grow_to(size_t n)
   {
   if(n > size())
      {
      if(n <= m_reg.capacity())
         m_reg.resize(m_reg.capacity());
      else
         m_reg.resize(round_up(n, 8));
      }
   }

/*
* Encode this number into bytes
*/
void BigInt::binary_encode(uint8_t output[]) const
   {
   const size_t sig_bytes = bytes();
   for(size_t i = 0; i != sig_bytes; ++i)
      output[sig_bytes-i-1] = byte_at(i);
   }

/*
* Set this number to the value in buf
*/
void BigInt::binary_decode(const uint8_t buf[], size_t length)
   {
   const size_t WORD_BYTES = sizeof(word);

   clear();
   m_reg.resize(round_up((length / WORD_BYTES) + 1, 8));

   for(size_t i = 0; i != length / WORD_BYTES; ++i)
      {
      const size_t top = length - WORD_BYTES*i;
      for(size_t j = WORD_BYTES; j > 0; --j)
         m_reg[i] = (m_reg[i] << 8) | buf[top - j];
      }

   for(size_t i = 0; i != length % WORD_BYTES; ++i)
      m_reg[length / WORD_BYTES] = (m_reg[length / WORD_BYTES] << 8) | buf[i];
   }

void BigInt::shrink_to_fit(size_t min_size)
   {
   const size_t words = std::max(min_size, sig_words());
   m_reg.resize(words);
   }

void BigInt::const_time_lookup(secure_vector<word>& output,
                               const std::vector<BigInt>& vec,
                               size_t idx)
   {
   const size_t words = output.size();

   clear_mem(output.data(), output.size());

   CT::poison(&idx, sizeof(idx));

   for(size_t i = 0; i != vec.size(); ++i)
      {
      BOTAN_ASSERT(vec[i].size() >= words,
                   "Word size as expected in const_time_lookup");

      const word mask = CT::is_equal(i, idx);

      for(size_t w = 0; w != words; ++w)
         output[w] |= CT::select<word>(mask, vec[i].word_at(w), 0);
      }

   CT::unpoison(idx);
   CT::unpoison(output.data(), output.size());
   }

}