path: root/src/lib/math/bigint/big_ops2.cpp

/*
* (C) 1999-2007,2018 Jack Lloyd
*     2016 Matthias Gierlings
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

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

namespace Botan {

BigInt& BigInt::add(const word y[], size_t y_words, Sign y_sign)
   {
   const size_t x_sw = sig_words();

   grow_to(std::max(x_sw, y_words) + 1);

   if(sign() == y_sign)
      {
      bigint_add2(mutable_data(), size() - 1, y, y_words);
      }
   else
      {
      const int32_t relative_size = bigint_cmp(data(), x_sw, y, y_words);

      if(relative_size >= 0)
         {
         // *this >= y
         bigint_sub2(mutable_data(), x_sw, y, y_words);
         }
      else
         {
         // *this < y
         bigint_sub2_rev(mutable_data(), y, y_words);
         }

      //this->sign_fixup(relative_size, y_sign);
      if(relative_size < 0)
         set_sign(y_sign);
      else if(relative_size == 0)
         set_sign(Positive);
      }

   return (*this);
   }

BigInt& BigInt::mod_add(const BigInt& s, const BigInt& mod, secure_vector<word>& ws)
   {
   if(this->is_negative() || s.is_negative() || mod.is_negative())
      throw Invalid_Argument("BigInt::mod_add expects all arguments are positive");

   BOTAN_DEBUG_ASSERT(*this < mod);
   BOTAN_DEBUG_ASSERT(s < mod);

   /*
   t + s or t + s - p == t - (p - s)

   So first compute ws = p - s

   Then compute t + s and t - ws

   If t - ws does not borrow, then that is the correct valued
   */

   const size_t mod_sw = mod.sig_words();
   BOTAN_ARG_CHECK(mod_sw > 0, "BigInt::mod_add modulus must be positive");

   this->grow_to(mod_sw);
   s.grow_to(mod_sw);

   // First mod_sw for p - s, 2*mod_sw for bigint_addsub workspace
   if(ws.size() < 3*mod_sw)
      ws.resize(3*mod_sw);

   word borrow = bigint_sub3(&ws[0], mod.data(), mod_sw, s.data(), mod_sw);
   CT::unpoison(borrow);
   BOTAN_ASSERT_NOMSG(borrow == 0);

   // Compute t - ws
   borrow = bigint_sub3(&ws[mod_sw], this->data(), mod_sw, &ws[0], mod_sw);

   // Compute t + s
   bigint_add3_nc(&ws[mod_sw*2], this->data(), mod_sw, s.data(), mod_sw);

   CT::conditional_copy_mem(borrow, &ws[0], &ws[mod_sw*2], &ws[mod_sw], mod_sw);
   set_words(&ws[0], mod_sw);

   return (*this);
   }

BigInt& BigInt::mod_sub(const BigInt& s, const BigInt& mod, secure_vector<word>& ws)
   {
   if(this->is_negative() || s.is_negative() || mod.is_negative())
      throw Invalid_Argument("BigInt::mod_sub expects all arguments are positive");

   // We are assuming in this function that *this and s are no more than mod_sw words long
   BOTAN_DEBUG_ASSERT(*this < mod);
   BOTAN_DEBUG_ASSERT(s < mod);

   const size_t mod_sw = mod.sig_words();

   this->grow_to(mod_sw);
   s.grow_to(mod_sw);

   if(ws.size() < mod_sw)
      ws.resize(mod_sw);

#if 0
   //Faster but not const time:

   // Compute t - s
   word borrow = bigint_sub3(ws.data(), data(), mod_sw, s.data(), mod_sw);

   if(borrow)
      {
      // If t < s, instead compute p - (s - t)
      bigint_sub2_rev(mutable_data(), s.data(), mod_sw);
      bigint_sub2_rev(mutable_data(), mod.data(), mod_sw);
      }
   else
      {
      // No borrow so we already have the result we need
      swap_reg(ws);
      }
#else
   if(mod_sw == 4)
      bigint_mod_sub_n<4>(mutable_data(), s.data(), mod.data(), ws.data());
   else if(mod_sw == 6)
      bigint_mod_sub_n<6>(mutable_data(), s.data(), mod.data(), ws.data());
   else
      bigint_mod_sub(mutable_data(), s.data(), mod.data(), mod_sw, ws.data());
#endif

   return (*this);
   }

BigInt& BigInt::mod_mul(uint8_t y, const BigInt& mod, secure_vector<word>& ws)
   {
   BOTAN_ARG_CHECK(this->is_negative() == false, "*this must be positive");
   BOTAN_ARG_CHECK(y < 16, "y too large");

   BOTAN_DEBUG_ASSERT(*this < mod);

   switch(y)
      {
      case 2:
         *this <<= 1;
         break;
      case 4:
         *this <<= 2;
         break;
      case 8:
         *this <<= 3;
         break;
      default:
         *this *= static_cast<word>(y);
         break;
      }

   this->reduce_below(mod, ws);
   return (*this);
   }

BigInt& BigInt::rev_sub(const word y[], size_t y_sw, secure_vector<word>& ws)
   {
   if(this->sign() != BigInt::Positive)
      throw Invalid_State("BigInt::sub_rev requires this is positive");

   const size_t x_sw = this->sig_words();

   ws.resize(std::max(x_sw, y_sw));
   clear_mem(ws.data(), ws.size());

   const int32_t relative_size = bigint_sub_abs(ws.data(), data(), x_sw, y, y_sw);

   if(relative_size > 0)
      this->flip_sign();

   this->swap_reg(ws);

   return (*this);
   }

/*
* Multiplication Operator
*/
BigInt& BigInt::operator*=(const BigInt& y)
   {
   secure_vector<word> ws;
   return this->mul(y, ws);
   }

BigInt& BigInt::mul(const BigInt& y, secure_vector<word>& ws)
   {
   const size_t x_sw = sig_words();
   const size_t y_sw = y.sig_words();
   set_sign((sign() == y.sign()) ? Positive : Negative);

   if(x_sw == 0 || y_sw == 0)
      {
      clear();
      set_sign(Positive);
      }
   else if(x_sw == 1 && y_sw)
      {
      grow_to(y_sw + 1);
      bigint_linmul3(mutable_data(), y.data(), y_sw, word_at(0));
      }
   else if(y_sw == 1 && x_sw)
      {
      grow_to(x_sw + 1);
      bigint_linmul2(mutable_data(), x_sw, y.word_at(0));
      }
   else
      {
      const size_t new_size = x_sw + y_sw + 1;
      ws.resize(new_size);
      secure_vector<word> z_reg(new_size);

      bigint_mul(z_reg.data(), z_reg.size(),
                 data(), size(), x_sw,
                 y.data(), y.size(), y_sw,
                 ws.data(), ws.size());

      this->swap_reg(z_reg);
      }

   return (*this);
   }

BigInt& BigInt::square(secure_vector<word>& ws)
   {
   const size_t sw = sig_words();

   secure_vector<word> z(2*sw);
   ws.resize(z.size());

   bigint_sqr(z.data(), z.size(),
              data(), size(), sw,
              ws.data(), ws.size());

   swap_reg(z);
   set_sign(BigInt::Positive);

   return (*this);
   }

BigInt& BigInt::operator*=(word y)
   {
   if(y == 0)
      {
      clear();
      set_sign(Positive);
      }

   const size_t x_sw = sig_words();

   if(size() < x_sw + 1)
      grow_to(x_sw + 1);
   bigint_linmul2(mutable_data(), x_sw, y);

   return (*this);
   }

/*
* Division Operator
*/
BigInt& BigInt::operator/=(const BigInt& y)
   {
   if(y.sig_words() == 1 && is_power_of_2(y.word_at(0)))
      (*this) >>= (y.bits() - 1);
   else
      (*this) = (*this) / y;
   return (*this);
   }

/*
* Modulo Operator
*/
BigInt& BigInt::operator%=(const BigInt& mod)
   {
   return (*this = (*this) % mod);
   }

/*
* Modulo Operator
*/
word BigInt::operator%=(word mod)
   {
   if(mod == 0)
      throw BigInt::DivideByZero();

   word remainder = 0;

   if(is_power_of_2(mod))
       {
       remainder = (word_at(0) & (mod - 1));
       }
   else
      {
      const size_t sw = sig_words();
      for(size_t i = sw; i > 0; --i)
         remainder = bigint_modop(remainder, word_at(i-1), mod);
      }

   if(remainder && sign() == BigInt::Negative)
      remainder = mod - remainder;

   m_data.set_to_zero();
   m_data.set_word_at(0, remainder);
   set_sign(BigInt::Positive);
   return remainder;
   }

/*
* Left Shift Operator
*/
BigInt& BigInt::operator<<=(size_t shift)
   {
   if(shift)
      {
      const size_t shift_words = shift / BOTAN_MP_WORD_BITS;
      const size_t shift_bits  = shift % BOTAN_MP_WORD_BITS;
      const size_t words = sig_words();

      /*
      * FIXME - if shift_words == 0 && the top shift_bits of the top word
      * are zero then we know that no additional word is needed and can
      * skip the allocation.
      */
      const size_t needed_size = words + shift_words + (shift_bits ? 1 : 0);

      m_data.grow_to(needed_size);

      bigint_shl1(m_data.mutable_data(), words, shift_words, shift_bits);
      }

   return (*this);
   }

/*
* Right Shift Operator
*/
BigInt& BigInt::operator>>=(size_t shift)
   {
   if(shift)
      {
      const size_t shift_words = shift / BOTAN_MP_WORD_BITS;
      const size_t shift_bits  = shift % BOTAN_MP_WORD_BITS;

      bigint_shr1(m_data.mutable_data(), m_data.size(), shift_words, shift_bits);

      if(is_negative() && is_zero())
         set_sign(Positive);
      }

   return (*this);
   }

}