lll_qp.cpp

NTL is a high-performance, portable C++ library providing data structures and algorithms for manipul

   if (bound == 0) {
      // we tolerate a 15% loss of precision in computing
      // inner products in ComputeGS.

      bound = 1;
      for (i = 2*long(0.15*2*NTL_DOUBLE_PRECISION); i > 0; i--) {
         bound = bound * 2;
      }
   }


   quad_float half = to_quad_float(0.5);
   quad_float half_plus_fudge = 0.5 + red_fudge;

   quit = 0;
   k = init_k;

   vec_long st_mem;
   st_mem.SetLength(m+2);
   long *st = st_mem.elts();

   for (i = 1; i < k; i++)
      st[i] = i;

   for (i = k; i <= m+1; i++)
      st[i] = 1;

   quad_float *buf;
   buf = NTL_NEW_OP quad_float [m+1];
   if (!buf) Error("out of memory in lll_LLL_QP");

   vec_long in_vec_mem;
   in_vec_mem.SetLength(n+1);
   long *in_vec = in_vec_mem.elts();

   double *max_b;
   max_b = NTL_NEW_OP double [m+1];
   if (!max_b) Error("out of memory in lll_LLL_QP");

   for (i = 1; i <= m; i++)
      max_b[i] = max_abs(B1[i], n);

   long in_float;


   long rst;
   long counter;

   long trigger_index;
   long small_trigger;
   long cnt;

   long max_k = 0;

   double tt;

   while (k <= m) {

      if (k > max_k) {
         max_k = k;
      }

      if (verbose) {
         tt = GetTime();

         if (tt > LastTime + LLLStatusInterval)
            LLLStatus(max_k, tt, m, B);
      }


      if (st[k] == k)
         rst = 1;
      else
         rst = k;

      if (st[k] < st[k+1]) st[k+1] = st[k];
      ComputeGS(B, B1, mu, b, c, k, bound, st[k], buf);
      CheckFinite(&c[k]);
      st[k] = k;

      counter = 0;
      trigger_index = k;
      small_trigger = 0;
      cnt = 0;

      do {
         // size reduction

         counter++;
         if (counter > 10000) {
            cerr << "LLL_QP: warning--possible infinite loop\n";
            counter = 0;
         }


         Fc1 = 0;
   
         for (j = rst-1; j >= 1; j--) {
            t1 = fabs(mu[k][j]);
            if (t1 > half_plus_fudge) {

               if (!Fc1) {
                  if (j > trigger_index ||
                      (j == trigger_index && small_trigger)) {

                     cnt++;

                     if (cnt > 10) {
                        inc_red_fudge();
                        half_plus_fudge = 0.5 + red_fudge;
                        cnt = 0;
                     }
                  }

                  trigger_index = j;
                  small_trigger = (t1 < 4);

                  Fc1 = 1;
                  RowTransformStart(B1[k], in_vec, in_float, n);
               }


   
               mu1 = mu[k][j];
               if (mu1 >= 0)
                  mu1 = ceil(mu1-half);
               else
                  mu1 = floor(mu1+half);
   
   
               quad_float *mu_k = mu[k];
               quad_float *mu_j = mu[j];
  
               if (mu1 == 1) {
                  for (i = 1; i <= j-1; i++)
                     mu_k[i] -= mu_j[i];
               }
               else if (mu1 == -1) {
                  for (i = 1; i <= j-1; i++)
                     mu_k[i] += mu_j[i];
               }
               else {
                  for (i = 1; i <= j-1; i++)
                     mu_k[i] -= mu1*mu_j[i];
               }

               // cout << j << " " << mu[k][j] << " " << mu1 << "\n";
  
               mu_k[j] -= mu1;

               conv(MU, mu1);

   
               RowTransform(B(k), B(j), MU, B1[k], B1[j], in_vec,
                            max_b[k], max_b[j], in_float);

               if (U) RowTransform((*U)(k), (*U)(j), MU);
            }
         }

         if (Fc1) {
            RowTransformFinish(B(k), B1[k], in_vec);
            max_b[k] = max_abs(B1[k], n);
   
            b[k] = InnerProduct(B1[k], B1[k], n);
            CheckFinite(&b[k]);

            ComputeGS(B, B1, mu, b, c, k, bound, 1, buf);
            CheckFinite(&c[k]);

         }
      } while (Fc1);

      if (check && (*check)(B(k))) 
         quit = 1;

      if (b[k] == 0) {
         for (i = k; i < m; i++) {
            // swap i, i+1
            swap(B(i), B(i+1));
            tp = B1[i]; B1[i] = B1[i+1]; B1[i+1] = tp;
            t1 = b[i]; b[i] = b[i+1]; b[i+1] = t1;
            dt1 = max_b[i]; max_b[i] = max_b[i+1]; max_b[i+1] = dt1;
            if (U) swap((*U)(i), (*U)(i+1));
         }

         for (i = k; i <= m+1; i++) st[i] = 1;

         m--;
         if (quit) break;
         continue;
      }

      if (quit) break;

      if (deep > 0) {
         // deep insertions
   
         quad_float cc = b[k];
         long l = 1;
         while (l <= k-1 && delta*c[l] <= cc) {
            cc = cc - mu[k][l]*mu[k][l]*c[l];
            l++;
         }
   
         if (l <= k-1 && (l <= deep || k-l <= deep)) {
            // deep insertion at position l
   
            for (i = k; i > l; i--) {
               // swap rows i, i-1
               swap(B(i), B(i-1));
               tp = B1[i]; B1[i] = B1[i-1]; B1[i-1] = tp;
               tp = mu[i]; mu[i] = mu[i-1]; mu[i-1] = tp;
               t1 = b[i]; b[i] = b[i-1]; b[i-1] = t1;
               dt1 = max_b[i]; max_b[i] = max_b[i-1]; max_b[i-1] = dt1;
               if (U) swap((*U)(i), (*U)(i-1));
            }
   
            k = l;
            NumSwaps++;
            continue;
         }
      } // end deep insertions

      // test LLL reduction condition

      if (k > 1 && delta*c[k-1] > c[k] + mu[k][k-1]*mu[k][k-1]*c[k-1]) {
         // swap rows k, k-1
         swap(B(k), B(k-1));
         tp = B1[k]; B1[k] = B1[k-1]; B1[k-1] = tp;
         tp = mu[k]; mu[k] = mu[k-1]; mu[k-1] = tp;
         t1 = b[k]; b[k] = b[k-1]; b[k-1] = t1;
         dt1 = max_b[k]; max_b[k] = max_b[k-1]; max_b[k-1] = dt1;
         if (U) swap((*U)(k), (*U)(k-1));

         k--;
         NumSwaps++;
         // cout << "- " << k << "\n";
      }
      else {
         k++;
         // cout << "+ " << k << "\n";
      }
   }

   if (verbose) {
      LLLStatus(m+1, GetTime(), m, B);
   }


   delete [] buf;
   delete [] max_b;

   return m;
}

static
long LLL_QP(mat_ZZ& B, mat_ZZ* U, quad_float delta, long deep, 
           LLLCheckFct check)
{
   long m = B.NumRows();
   long n = B.NumCols();

   long i, j;
   long new_m, dep, quit;
   quad_float s;
   ZZ MU;
   quad_float mu1;

   quad_float t1;
   ZZ T1;

   init_red_fudge();

   if (U) ident(*U, m);

   quad_float **B1;  // approximates B

   typedef quad_float *quad_floatptr;

   B1 = NTL_NEW_OP quad_floatptr[m+1];
   if (!B1) Error("LLL_QP: out of memory");

   for (i = 1; i <= m; i++) {
      B1[i] = NTL_NEW_OP quad_float[n+1];
      if (!B1[i]) Error("LLL_QP: out of memory");
   }

   quad_float **mu;
   mu = NTL_NEW_OP quad_floatptr[m+1];
   if (!mu) Error("LLL_QP: out of memory");

   for (i = 1; i <= m; i++) {
      mu[i] = NTL_NEW_OP quad_float[m+1];
      if (!mu[i]) Error("LLL_QP: out of memory");
   }

   quad_float *c; // squared lengths of Gramm-Schmidt basis vectors

   c = NTL_NEW_OP quad_float[m+1];
   if (!c) Error("LLL_QP: out of memory");

   quad_float *b; // squared lengths of basis vectors

   b = NTL_NEW_OP quad_float[m+1];
   if (!b) Error("LLL_QP: out of memory");



   for (i = 1; i <=m; i++)
      for (j = 1; j <= n; j++) {
         conv(B1[i][j], B(i, j));
         CheckFinite(&B1[i][j]);
      }


         
   for (i = 1; i <= m; i++) {
      b[i] = InnerProduct(B1[i], B1[i], n);
      CheckFinite(&b[i]);
   }


   new_m = ll_LLL_QP(B, U, delta, deep, check, B1, mu, b, c, m, 1, quit);
   dep = m - new_m;
   m = new_m;

   if (dep > 0) {
      // for consistency, we move all of the zero rows to the front

      for (i = 0; i < m; i++) {
         swap(B(m+dep-i), B(m-i));
         if (U) swap((*U)(m+dep-i), (*U)(m-i));
      }
   }


   // clean-up

   for (i = 1; i <= m; i++) {
      delete [] B1[i];
   }

   delete [] B1;

   for (i = 1; i <= m; i++) {
      delete [] mu[i];
   }

   delete [] mu;

   delete [] c;

   delete [] b;

   return m;
}

         

long LLL_QP(mat_ZZ& B, double delta, long deep, LLLCheckFct check,
            long verb)
{
   verbose = verb;
   NumSwaps = 0;
   if (verbose) {
      StartTime = GetTime();
      LastTime = StartTime;
   }

   if (delta < 0.50 || delta >= 1) Error("LLL_QP: bad delta");
   if (deep < 0) Error("LLL_QP: bad deep");
   return LLL_QP(B, 0, to_quad_float(delta), deep, check);
}

long LLL_QP(mat_ZZ& B, mat_ZZ& U, double delta, long deep, 
           LLLCheckFct check, long verb)
{
   verbose = verb;
   NumSwaps = 0;
   if (verbose) {
      StartTime = GetTime();
      LastTime = StartTime;
   }


   if (delta < 0.50 || delta >= 1) Error("LLL_QP: bad delta");
   if (deep < 0) Error("LLL_QP: bad deep");
   return LLL_QP(B, &U, to_quad_float(delta), deep, check);
}



static vec_quad_float BKZConstant;

static
void ComputeBKZConstant(long beta, long p)
{
   const quad_float c_PI = 
      to_quad_float("3.141592653589793238462643383279502884197");
   const quad_float LogPI = 
      to_quad_float("1.144729885849400174143427351353058711647");

   BKZConstant.SetLength(beta-1);

   vec_quad_float Log;
   Log.SetLength(beta);


   long i, j, k;
   quad_float x, y;

   for (j = 1; j <= beta; j++)
      Log(j) = log(to_quad_float(j));

   for (i = 1; i <= beta-1; i++) {
      // First, we compute x = gamma(i/2)^{2/i}

      k = i/2;

      if ((i & 1) == 0) { // i even
         x = 0;
         for (j = 1; j <= k; j++)
            x = x + Log(j);
          
         x = x * (1/to_quad_float(k));

         x = exp(x);
      }
      else { // i odd
         x = 0;
         for (j = k + 2; j <= 2*k + 2; j++)
            x = x + Log(j);

         x = 0.5*LogPI + x - 2*(k+1)*Log(2);

         x = x * (2.0/to_quad_float(i));

         x = exp(x);
      }

      // Second, we compute y = 2^{2*p/i}

      y = -(2*p/to_quad_float(i))*Log(2);
      y = exp(y);

      BKZConstant(i) = x*y/c_PI;
   }
}

static vec_quad_float BKZThresh;

static 
void ComputeBKZThresh(quad_float *c, long beta)
{
   BKZThresh.SetLength(beta-1);

   long i;
   quad_float x;

   x = 0;

   for (i = 1; i <= beta-1; i++) {
      x += log(c[i-1]);
      BKZThresh(i) = exp(x/to_quad_float(i))*BKZConstant(i);
      if (!IsFinite(&BKZThresh(i))) BKZThresh(i) = 0;
   }
}


static 
void BKZStatus(double tt, double enum_time, unsigned long NumIterations, 
               unsigned long NumTrivial, unsigned long NumNonTrivial, 
               unsigned long NumNoOps, long m, 
               const mat_ZZ& B)
{
   cerr << "---- BKZ_QP status ----\n";
   cerr << "elapsed time: ";
   PrintTime(cerr, tt-StartTime);
   cerr << ", enum time: ";
   PrintTime(cerr, enum_time);
   cerr << ", iter: " << NumIterations << "\n";
   cerr << "triv: " << NumTrivial;
   cerr << ", nontriv: " << NumNonTrivial;
   cerr << ", no ops: " << NumNoOps;
   cerr << ", rank: " << m;
   cerr << ", swaps: " << NumSwaps << "\n";



   ZZ t1;
   long i;
   double prodlen = 0;

   for (i = 1; i <= m; i++) {
      InnerProduct(t1, B(i), B(i));
      if (!IsZero(t1))
         prodlen += log(t1);
   }

   cerr << "log of prod of lengths: " << prodlen/(2.0*log(2.0)) << "\n";


   if (LLLDumpFile) {
      cerr << "dumping to " << LLLDumpFile << "...";

      ofstream f;
      OpenWrite(f, LLLDumpFile);
      
      f << "[";
      for (i = 1; i <= m; i++) {
         f << B(i) << "\n";
      }
      f << "]\n";

      f.close();