big_ops3.cpp

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/*
* BigInt Binary Operators
* (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/divide.h>
#include <botan/internal/mp_core.h>
#include <algorithm>
 
namespace Botan {
 
//static
BigInt BigInt::add2(const BigInt& x, const word y[], size_t y_size, BigInt::Sign y_sign) {
   const size_t x_sw = x.sig_words();
 
   BigInt z = BigInt::with_capacity(std::max(x_sw, y_size) + 1);
 
   if(x.sign() == y_sign) {
      const word carry = bigint_add3(z.mutable_data(), x._data(), x_sw, y, y_size);
      z.mutable_data()[std::max(x_sw, y_size)] += carry;
      z.set_sign(x.sign());
   } else {
      const int32_t relative_size = bigint_cmp(x.data(), x_sw, y, y_size);
 
      if(relative_size < 0) {
         // x < y so z = abs(y - x)
         // NOLINTNEXTLINE(*-suspicious-call-argument) intentionally swapping x and y here
         bigint_sub3(z.mutable_data(), y, y_size, x.data(), x_sw);
         z.set_sign(y_sign);
      } else if(relative_size == 0) {
         // Positive zero (nothing to do in this case)
      } else {
         /*
         * We know at this point that x >= y so if y_size is larger than
         * x_sw, we are guaranteed they are just leading zeros which can
         * be ignored
         */
         y_size = std::min(x_sw, y_size);
         bigint_sub3(z.mutable_data(), x.data(), x_sw, y, y_size);
         z.set_sign(x.sign());
      }
   }
 
   return z;
}
 
/*
* Multiplication Operator
*/
BigInt operator*(const BigInt& x, const BigInt& y) {
   const size_t x_sw = x.sig_words();
   const size_t y_sw = y.sig_words();
 
   BigInt z = BigInt::with_capacity(x.size() + y.size());
 
   if(x_sw == 1 && y_sw > 0) {
      bigint_linmul3(z.mutable_data(), y._data(), y_sw, x.word_at(0));
   } else if(y_sw == 1 && x_sw > 0) {
      bigint_linmul3(z.mutable_data(), x._data(), x_sw, y.word_at(0));
   } else if(x_sw > 0 && y_sw > 0) {
      secure_vector<word> workspace(z.size());
 
      bigint_mul(z.mutable_data(),
                 z.size(),
                 x._data(),
                 x.size(),
                 x_sw,
                 y._data(),
                 y.size(),
                 y_sw,
                 workspace.data(),
                 workspace.size());
   }
 
   z.cond_flip_sign(x_sw > 0 && y_sw > 0 && x.sign() != y.sign());
 
   return z;
}
 
/*
* Multiplication Operator
*/
BigInt operator*(const BigInt& x, word y) {
   const size_t x_sw = x.sig_words();
 
   BigInt z = BigInt::with_capacity(x_sw + 1);
 
   if(x_sw > 0 && y > 0) {
      bigint_linmul3(z.mutable_data(), x._data(), x_sw, y);
      z.set_sign(x.sign());
   }
 
   return z;
}
 
/*
* Division Operator
*/
BigInt operator/(const BigInt& x, const BigInt& y) {
   if(y.sig_words() == 1 && y.is_positive()) {
      return x / y.word_at(0);
   }
 
   BigInt q;
   BigInt r;
   vartime_divide(x, y, q, r);
   return q;
}
 
/*
* Division Operator
*/
BigInt operator/(const BigInt& x, word y) {
   if(y == 0) {
      throw Invalid_Argument("BigInt::operator/ divide by zero");
   }
 
   BigInt q;
   word r = 0;
   ct_divide_word(x, y, q, r);
   return q;
}
 
/*
* Modulo Operator
*/
BigInt operator%(const BigInt& n, const BigInt& mod) {
   if(mod.is_zero()) {
      throw Invalid_Argument("BigInt::operator% divide by zero");
   }
   if(mod.is_negative()) {
      throw Invalid_Argument("BigInt::operator% modulus must be > 0");
   }
   if(n.is_positive() && mod.is_positive() && n < mod) {
      return n;
   }
 
   if(mod.sig_words() == 1) {
      return BigInt::from_word(n % mod.word_at(0));
   }
 
   BigInt q;
   BigInt r;
   vartime_divide(n, mod, q, r);
   return r;
}
 
/*
* Modulo Operator
*/
word operator%(const BigInt& n, word mod) {
   if(mod == 0) {
      throw Invalid_Argument("BigInt::operator% divide by zero");
   }
 
   if(mod == 1) {
      return 0;
   }
 
   word remainder = 0;
 
   if(n.is_positive() && is_power_of_2(mod)) {
      remainder = (n.word_at(0) & (mod - 1));
   } else {
      const divide_precomp redc_mod(mod);
      const size_t sw = n.sig_words();
      for(size_t i = sw; i > 0; --i) {
         remainder = redc_mod.vartime_mod_2to1(remainder, n.word_at(i - 1));
      }
   }
 
   if(remainder != 0 && n.sign() == BigInt::Negative) {
      return mod - remainder;
   }
   return remainder;
}
 
/*
* Left Shift Operator
*/
BigInt operator<<(const BigInt& x, size_t shift) {
   if(x.is_zero()) {
      return BigInt::zero();
   }
 
   const size_t x_sw = x.sig_words();
 
   const size_t new_size = x_sw + (shift + WordInfo<word>::bits - 1) / WordInfo<word>::bits;
   BigInt y = BigInt::with_capacity(new_size);
   bigint_shl2(y.mutable_data(), x._data(), x_sw, shift);
   y.set_sign(x.sign());
   return y;
}
 
/*
* Right Shift Operator
*/
BigInt operator>>(const BigInt& x, size_t shift) {
   const size_t shift_words = shift / WordInfo<word>::bits;
   const size_t x_sw = x.sig_words();
 
   if(shift_words >= x_sw) {
      return BigInt::zero();
   }
 
   BigInt y = BigInt::with_capacity(x_sw - shift_words);
   bigint_shr2(y.mutable_data(), x._data(), x_sw, shift);
 
   if(x.is_negative() && y.is_zero()) {
      y.set_sign(BigInt::Positive);
   } else {
      y.set_sign(x.sign());
   }
 
   return y;
}
 
}  // namespace Botan