isl_scan.c

   1 /*
   2  * Copyright 2008-2009 Katholieke Universiteit Leuven
   3  *
   4  * Use of this software is governed by the GNU LGPLv2.1 license
   5  *
   6  * Written by Sven Verdoolaege, K.U.Leuven, Departement
   7  * Computerwetenschappen, Celestijnenlaan 200A, B-3001 Leuven, Belgium
   8  */
   9
  10 #include "isl_basis_reduction.h"
  11 #include "isl_scan.h"
  12 #include "isl_seq.h"
  13 #include "isl_tab.h"
  14
  15 /* Call callback->add with the current sample value of the tableau "tab".
  16  */
  17 static int add_solution(struct isl_tab *tab, struct isl_scan_callback *callback)
  18 {
  19         struct isl_vec *sample;
  20
  21         if (!tab)
  22                 return -1;
  23         sample = isl_tab_get_sample_value(tab);
  24         if (!sample)
  25                 return -1;
  26
  27         return callback->add(callback, sample);
  28 }
  29
  30 static int scan_0D(struct isl_basic_set *bset,
  31         struct isl_scan_callback *callback)
  32 {
  33         struct isl_vec *sample;
  34
  35         sample = isl_vec_alloc(bset->ctx, 1);
  36         isl_basic_set_free(bset);
  37
  38         if (!sample)
  39                 return -1;
  40
  41         isl_int_set_si(sample->el[0], 1);
  42
  43         return callback->add(callback, sample);
  44 }
  45
  46 /* Look for all integer points in "bset", which is assumed to be unbounded,
  47  * and call callback->add on each of them.
  48  *
  49  * We first compute a reduced basis for the set and then scan
  50  * the set in the directions of this basis.
  51  * We basically perform a depth first search, where in each level i
  52  * we compute the range in the i-th basis vector direction, given
  53  * fixed values in the directions of the previous basis vector.
  54  * We then add an equality to the tableau fixing the value in the
  55  * direction of the current basis vector to each value in the range
  56  * in turn and then continue to the next level.
  57  *
  58  * The search is implemented iteratively.  "level" identifies the current
  59  * basis vector.  "init" is true if we want the first value at the current
  60  * level and false if we want the next value.
  61  * Solutions are added in the leaves of the search tree, i.e., after
  62  * we have fixed a value in each direction of the basis.
  63  */
  64 int isl_basic_set_scan(struct isl_basic_set *bset,
  65         struct isl_scan_callback *callback)
  66 {
  67         unsigned dim;
  68         struct isl_mat *B = NULL;
  69         struct isl_tab *tab = NULL;
  70         struct isl_vec *min;
  71         struct isl_vec *max;
  72         struct isl_tab_undo **snap;
  73         int level;
  74         int init;
  75         enum isl_lp_result res;
  76
  77         if (!bset)
  78                 return -1;
  79
  80         dim = isl_basic_set_total_dim(bset);
  81         if (dim == 0)
  82                 return scan_0D(bset, callback);
  83
  84         min = isl_vec_alloc(bset->ctx, dim);
  85         max = isl_vec_alloc(bset->ctx, dim);
  86         snap = isl_alloc_array(bset->ctx, struct isl_tab_undo *, dim);
  87
  88         if (!min || !max || !snap)
  89                 goto error;
  90
  91         tab = isl_tab_from_basic_set(bset);
  92         if (!tab)
  93                 goto error;
  94
  95         tab->basis = isl_mat_identity(bset->ctx, 1 + dim);
  96         if (1)
  97                 tab = isl_tab_compute_reduced_basis(tab);
  98         if (!tab)
  99                 goto error;
 100         B = isl_mat_copy(tab->basis);
 101         if (!B)
 102                 goto error;
 103
 104         level = 0;
 105         init = 1;
 106
 107         while (level >= 0) {
 108                 int empty = 0;
 109                 if (init) {
 110                         res = isl_tab_min(tab, B->row[1 + level],
 111                                     bset->ctx->one, &min->el[level], NULL, 0);
 112                         if (res == isl_lp_empty)
 113                                 empty = 1;
 114                         if (res == isl_lp_error || res == isl_lp_unbounded)
 115                                 goto error;
 116                         isl_seq_neg(B->row[1 + level] + 1,
 117                                     B->row[1 + level] + 1, dim);
 118                         res = isl_tab_min(tab, B->row[1 + level],
 119                                     bset->ctx->one, &max->el[level], NULL, 0);
 120                         isl_seq_neg(B->row[1 + level] + 1,
 121                                     B->row[1 + level] + 1, dim);
 122                         isl_int_neg(max->el[level], max->el[level]);
 123                         if (res == isl_lp_empty)
 124                                 empty = 1;
 125                         if (res == isl_lp_error || res == isl_lp_unbounded)
 126                                 goto error;
 127                         snap[level] = isl_tab_snap(tab);
 128                 } else
 129                         isl_int_add_ui(min->el[level], min->el[level], 1);
 130
 131                 if (empty || isl_int_gt(min->el[level], max->el[level])) {
 132                         level--;
 133                         init = 0;
 134                         if (level >= 0)
 135                                 if (isl_tab_rollback(tab, snap[level]) < 0)
 136                                         goto error;
 137                         continue;
 138                 }
 139                 isl_int_neg(B->row[1 + level][0], min->el[level]);
 140                 tab = isl_tab_add_valid_eq(tab, B->row[1 + level]);
 141                 isl_int_set_si(B->row[1 + level][0], 0);
 142                 if (level < dim - 1) {
 143                         ++level;
 144                         init = 1;
 145                         continue;
 146                 }
 147                 if (add_solution(tab, callback) < 0)
 148                         goto error;
 149                 init = 0;
 150                 if (isl_tab_rollback(tab, snap[level]) < 0)
 151                         goto error;
 152         }
 153
 154         isl_tab_free(tab);
 155         free(snap);
 156         isl_vec_free(min);
 157         isl_vec_free(max);
 158         isl_basic_set_free(bset);
 159         isl_mat_free(B);
 160         return 0;
 161 error:
 162         isl_tab_free(tab);
 163         free(snap);
 164         isl_vec_free(min);
 165         isl_vec_free(max);
 166         isl_basic_set_free(bset);
 167         isl_mat_free(B);
 168         return -1;
 169 }