mp_monty.cpp

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/*
* Montgomery Reduction
* (C) 1999-2011 Jack Lloyd
*     2006 Luca Piccarreta
*
* Distributed under the terms of the Botan license
*/
 
#include <botan/internal/mp_core.h>
#include <botan/internal/mp_asm.h>
#include <botan/internal/mp_asmi.h>
#include <botan/mem_ops.h>
 
namespace Botan {
 
extern "C" {
 
/*
* Montgomery Reduction Algorithm
*/
void bigint_monty_redc(word z[], size_t z_size,
                       const word p[], size_t p_size,
                       word p_dash, word ws[])
   {
   const size_t blocks_of_8 = p_size - (p_size % 8);
 
   for(size_t i = 0; i != p_size; ++i)
      {
      word* z_i = z + i;
 
      const word y = z_i[0] * p_dash;
 
      /*
      bigint_linmul3(ws, p, p_size, y);
      bigint_add2(z_i, z_size - i, ws, p_size+1);
      */
 
      word carry = 0;
 
      for(size_t j = 0; j != blocks_of_8; j += 8)
         carry = word8_madd3(z_i + j, p + j, y, carry);
 
      for(size_t j = blocks_of_8; j != p_size; ++j)
         z_i[j] = word_madd3(p[j], y, z_i[j], &carry);
 
      word z_sum = z_i[p_size] + carry;
      carry = (z_sum < z_i[p_size]);
      z_i[p_size] = z_sum;
 
      for(size_t j = p_size + 1; carry && j != z_size - i; ++j)
         {
         ++z_i[j];
         carry = !z_i[j];
         }
      }
 
   word borrow = 0;
   for(size_t i = 0; i != p_size; ++i)
      ws[i] = word_sub(z[p_size + i], p[i], &borrow);
 
   ws[p_size] = word_sub(z[p_size+p_size], 0, &borrow);
 
   copy_mem(ws + p_size + 1, z + p_size, p_size + 1);
 
   copy_mem(z, ws + borrow*(p_size+1), p_size + 1);
   clear_mem(z + p_size + 1, z_size - p_size - 1);
   }
 
void bigint_monty_mul(word z[], size_t z_size,
                      const word x[], size_t x_size, size_t x_sw,
                      const word y[], size_t y_size, size_t y_sw,
                      const word p[], size_t p_size, word p_dash,
                      word ws[])
   {
   bigint_mul(&z[0], z_size, &ws[0],
              &x[0], x_size, x_sw,
              &y[0], y_size, y_sw);
 
   bigint_monty_redc(&z[0], z_size,
                     &p[0], p_size, p_dash,
                     &ws[0]);
   }
 
void bigint_monty_sqr(word z[], size_t z_size,
                      const word x[], size_t x_size, size_t x_sw,
                      const word p[], size_t p_size, word p_dash,
                      word ws[])
   {
   bigint_sqr(&z[0], z_size, &ws[0],
              &x[0], x_size, x_sw);
 
   bigint_monty_redc(&z[0], z_size,
                     &p[0], p_size, p_dash,
                     &ws[0]);
   }
 
}
 
}