big_ops2.cpp

Go to the documentation of this file.

/*
* (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/exceptn.h>
#include <botan/internal/bit_ops.h>
#include <botan/internal/mp_core.h>
 
namespace Botan {
 
BigInt& BigInt::operator+=(const BigInt& y) {
   if(&y == this) {
      return *this <<= 1;
   }
   return add(y._data(), y.sig_words(), y.sign());
}
 
BigInt& BigInt::operator-=(const BigInt& y) {
   if(&y == this) {
      this->clear();
      this->set_sign(Positive);
      return *this;
   }
   return sub(y._data(), y.sig_words(), y.sign());
}
 
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) {
      const word carry = bigint_add2(mutable_data(), size() - 1, y, y_words);
      mutable_data()[size() - 1] += carry;
   } 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: compute *this = y - *this
         bigint_sub2_rev(mutable_data(), y, y_words);
      }
 
      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->signum() < 0 || s.signum() < 0 || mod.signum() < 0) {
      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);
   }
 
   // NOLINTBEGIN(readability-container-data-pointer)
 
   word borrow = bigint_sub3(&ws[0], mod._data(), mod_sw, s._data(), mod_sw);
   BOTAN_DEBUG_ASSERT(borrow == 0);
   BOTAN_UNUSED(borrow);
 
   // Compute t - ws
   borrow = bigint_sub3(&ws[mod_sw], this->_data(), mod_sw, &ws[0], mod_sw);
 
   // Compute t + s
   bigint_add3(&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);
 
   // NOLINTEND(readability-container-data-pointer)
 
   return (*this);
}
 
BigInt& BigInt::mod_sub(const BigInt& s, const BigInt& mod, secure_vector<word>& ws) {
   if(this->signum() < 0 || s.signum() < 0 || mod.signum() < 0) {
      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);
   }
 
   const word borrow = bigint_sub3(ws.data(), mutable_data(), mod_sw, s._data(), mod_sw);
 
   // Conditionally add back the modulus
   bigint_cnd_add(borrow, ws.data(), mod._data(), mod_sw);
 
   unchecked_copy_memory(mutable_data(), ws.data(), mod_sw);
 
   return (*this);
}
 
BigInt& BigInt::mod_mul(uint8_t y, const BigInt& mod, secure_vector<word>& ws) {
   BOTAN_ARG_CHECK(this->signum() >= 0, "*this must be positive");
   BOTAN_ARG_CHECK(y < 16, "y too large");
 
   BOTAN_DEBUG_ASSERT(*this < mod);
 
   *this *= static_cast<word>(y);
   this->reduce_below(mod, ws);
   return (*this);
}
 
BigInt& BigInt::rev_sub(const word y[], size_t y_sw, secure_vector<word>& ws) {
   BOTAN_UNUSED(ws);
   BigInt y_bn;
   y_bn.m_data.set_words(y, y_sw);
   *this = y_bn - *this;
   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 > 0) {
      grow_to(y_sw + 1);
      bigint_linmul3(mutable_data(), y._data(), y_sw, word_at(0));
   } else {
      const size_t new_size = x_sw + y_sw + 1;
      if(ws.size() < new_size) {
         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 word carry = bigint_linmul2(mutable_data(), size(), y);
   set_word_at(size(), carry);
 
   return (*this);
}
 
/*
* Division Operator
*/
BigInt& BigInt::operator/=(const BigInt& y) {
   if(y.sig_words() == 1 && signum() >= 0 && y.signum() >= 0 && 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 Invalid_Argument("BigInt::operator%= divide by zero");
   }
 
   word remainder = 0;
 
   if(is_power_of_2(mod)) {
      remainder = (word_at(0) & (mod - 1));
   } else {
      const divide_precomp redc_mod(mod);
      const size_t sw = sig_words();
      for(size_t i = sw; i > 0; --i) {
         remainder = redc_mod.vartime_mod_2to1(remainder, word_at(i - 1));
      }
   }
 
   if(remainder != 0 && 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 >= 65536) {
      throw Invalid_Argument("BigInt left shift count too large");
   }
 
   const size_t sw = sig_words();
   const size_t new_size = sw + (shift + WordInfo<word>::bits - 1) / WordInfo<word>::bits;
 
   m_data.grow_to(new_size);
 
   bigint_shl1(m_data.mutable_data(), new_size, sw, shift);
 
   return (*this);
}
 
/*
* Right Shift Operator
*/
BigInt& BigInt::operator>>=(size_t shift) {
   bigint_shr1(m_data.mutable_data(), m_data.size(), shift);
 
   if(sig_words() == 0 && m_signedness == Negative) {
      m_signedness = Positive;
   }
 
   return (*this);
}
 
}  // namespace Botan