src/surf/maxmin.c

   1 /*      $Id$     */
   2
   3 /* Copyright (c) 2004 Arnaud Legrand. All rights reserved.                  */
   4
   5 /* This program is free software; you can redistribute it and/or modify it
   6  * under the terms of the license (GNU LGPL) which comes with this package. */
   7
   8
   9 #include "xbt/sysdep.h"
  10 #include "xbt/log.h"
  11 #include "xbt/mallocator.h"
  12 #include "maxmin_private.h"
  13 #include <stdlib.h>
  14 #include <stdio.h> /* sprintf */
  15 #include <math.h>
  16 XBT_LOG_NEW_DEFAULT_SUBCATEGORY(surf_maxmin, surf,
  17                                 "Logging specific to SURF (maxmin)");
  18
  19 static void *lmm_variable_mallocator_new_f(void);
  20 static void lmm_variable_mallocator_free_f(void *var);
  21 static void lmm_variable_mallocator_reset_f(void *var);
  22
  23 lmm_system_t lmm_system_new(void)
  24 {
  25   lmm_system_t l = NULL;
  26   s_lmm_variable_t var;
  27   s_lmm_constraint_t cnst;
  28
  29   l = xbt_new0(s_lmm_system_t, 1);
  30
  31   l->modified = 0;
  32   xbt_swag_init(&(l->variable_set),
  33                 xbt_swag_offset(var, variable_set_hookup));
  34   xbt_swag_init(&(l->constraint_set),
  35                 xbt_swag_offset(cnst, constraint_set_hookup));
  36
  37   xbt_swag_init(&(l->active_constraint_set),
  38                 xbt_swag_offset(cnst, active_constraint_set_hookup));
  39
  40   xbt_swag_init(&(l->saturated_variable_set),
  41                 xbt_swag_offset(var, saturated_variable_set_hookup));
  42   xbt_swag_init(&(l->saturated_constraint_set),
  43                 xbt_swag_offset(cnst, saturated_constraint_set_hookup));
  44
  45   l->variable_mallocator = xbt_mallocator_new(64,
  46                                               lmm_variable_mallocator_new_f,
  47                                               lmm_variable_mallocator_free_f,
  48                                               lmm_variable_mallocator_reset_f);
  49
  50   return l;
  51 }
  52
  53 void lmm_system_free(lmm_system_t sys)
  54 {
  55   lmm_variable_t var = NULL;
  56   lmm_constraint_t cnst = NULL;
  57
  58   while ((var = extract_variable(sys)))
  59     lmm_var_free(sys, var);
  60
  61   while ((cnst = extract_constraint(sys)))
  62     lmm_cnst_free(sys, cnst);
  63
  64   xbt_mallocator_free(sys->variable_mallocator);
  65   free(sys);
  66 }
  67
  68 void lmm_variable_disable(lmm_system_t sys, lmm_variable_t var)
  69 {
  70   int i;
  71   lmm_element_t elem = NULL;
  72
  73   XBT_IN2("(sys=%p, var=%p)", sys, var);
  74   sys->modified = 1;
  75
  76   for (i = 0; i < var->cnsts_number; i++) {
  77     elem = &var->cnsts[i];
  78     xbt_swag_remove(elem, &(elem->constraint->element_set));
  79     xbt_swag_remove(elem, &(elem->constraint->active_element_set));
  80     if (!xbt_swag_size(&(elem->constraint->element_set)))
  81       make_constraint_inactive(sys, elem->constraint);
  82   }
  83   var->cnsts_number = 0;
  84   XBT_OUT;
  85 }
  86
  87 static void lmm_var_free(lmm_system_t sys, lmm_variable_t var)
  88 {
  89
  90   lmm_variable_disable(sys, var);
  91   free(var->cnsts);
  92   xbt_mallocator_release(sys->variable_mallocator, var);
  93 }
  94
  95 static void lmm_cnst_free(lmm_system_t sys, lmm_constraint_t cnst)
  96 {
  97 /*   xbt_assert0(xbt_swag_size(&(cnst->element_set)), */
  98 /*            "This list should be empty!"); */
  99   remove_active_constraint(sys, cnst);
 100   free(cnst);
 101 }
 102
 103 lmm_constraint_t lmm_constraint_new(lmm_system_t sys, void *id,
 104                                     double bound_value)
 105 {
 106   lmm_constraint_t cnst = NULL;
 107   s_lmm_element_t elem;
 108
 109   cnst = xbt_new0(s_lmm_constraint_t, 1);
 110   cnst->id = id;
 111   xbt_swag_init(&(cnst->element_set),
 112                 xbt_swag_offset(elem, element_set_hookup));
 113   xbt_swag_init(&(cnst->active_element_set),
 114                 xbt_swag_offset(elem, active_element_set_hookup));
 115
 116   cnst->bound = bound_value;
 117   cnst->usage = 0;
 118   cnst->shared = 1;
 119   insert_constraint(sys, cnst);
 120
 121   return cnst;
 122 }
 123
 124 void lmm_constraint_shared(lmm_constraint_t cnst)
 125 {
 126   cnst->shared = 0;
 127 }
 128
 129 void lmm_constraint_free(lmm_system_t sys, lmm_constraint_t cnst)
 130 {
 131   remove_constraint(sys, cnst);
 132   lmm_cnst_free(sys, cnst);
 133 }
 134
 135 static void *lmm_variable_mallocator_new_f(void)
 136 {
 137   return xbt_new(s_lmm_variable_t, 1);
 138 }
 139
 140 static void lmm_variable_mallocator_free_f(void *var)
 141 {
 142   xbt_free(var);
 143 }
 144
 145 static void lmm_variable_mallocator_reset_f(void *var)
 146 {
 147   /* memset to zero like calloc */
 148   memset(var, 0, sizeof(s_lmm_variable_t));
 149 }
 150
 151 lmm_variable_t lmm_variable_new(lmm_system_t sys, void *id,
 152                                 double weight,
 153                                 double bound, int number_of_constraints)
 154 {
 155   lmm_variable_t var = NULL;
 156   int i;
 157
 158   XBT_IN5("(sys=%p, id=%p, weight=%f, bound=%f, num_cons =%d)",
 159           sys, id, weight, bound, number_of_constraints);
 160
 161   var = xbt_mallocator_get(sys->variable_mallocator);
 162   var->id = id;
 163   var->cnsts = xbt_new0(s_lmm_element_t, number_of_constraints);
 164   for (i = 0; i < number_of_constraints; i++) {
 165     /* Should be useless because of the
 166        calloc but it seems to help valgrind... */
 167     var->cnsts[i].element_set_hookup.next = NULL;
 168     var->cnsts[i].element_set_hookup.prev = NULL;
 169     var->cnsts[i].active_element_set_hookup.next = NULL;
 170     var->cnsts[i].active_element_set_hookup.prev = NULL;
 171     var->cnsts[i].constraint = NULL;
 172     var->cnsts[i].variable = NULL;
 173     var->cnsts[i].value = 0.0;
 174   }
 175   var->cnsts_size = number_of_constraints;
 176   var->cnsts_number = 0;        /* Should be useless because of the
 177                                    calloc but it seems to help valgrind... */
 178   var->weight = weight;
 179   var->bound = bound;
 180   var->value = 0.0;
 181   var->df = 0.0;
 182
 183   var->func_f = func_f_def;
 184   var->func_fp = func_fp_def;
 185   var->func_fpi = func_fpi_def;
 186
 187   if (weight)
 188     xbt_swag_insert_at_head(var, &(sys->variable_set));
 189   else
 190     xbt_swag_insert_at_tail(var, &(sys->variable_set));
 191   XBT_OUT;
 192   return var;
 193 }
 194
 195 void lmm_variable_free(lmm_system_t sys, lmm_variable_t var)
 196 {
 197   remove_variable(sys, var);
 198   lmm_var_free(sys, var);
 199 }
 200
 201 double lmm_variable_getvalue(lmm_variable_t var)
 202 {
 203   return (var->value);
 204 }
 205
 206 void lmm_expand(lmm_system_t sys, lmm_constraint_t cnst,
 207                 lmm_variable_t var, double value)
 208 {
 209   lmm_element_t elem = NULL;
 210
 211   sys->modified = 1;
 212
 213   xbt_assert0(var->cnsts_number < var->cnsts_size, "Too much constraints");
 214
 215   elem = &(var->cnsts[var->cnsts_number++]);
 216
 217   elem->value = value;
 218   elem->constraint = cnst;
 219   elem->variable = var;
 220
 221   if (var->weight)
 222     xbt_swag_insert_at_head(elem, &(elem->constraint->element_set));
 223   else
 224     xbt_swag_insert_at_tail(elem, &(elem->constraint->element_set));
 225
 226   make_constraint_active(sys, cnst);
 227 }
 228
 229 void lmm_expand_add(lmm_system_t sys, lmm_constraint_t cnst,
 230                     lmm_variable_t var, double value)
 231 {
 232   int i;
 233   sys->modified = 1;
 234
 235   for (i = 0; i < var->cnsts_number; i++)
 236     if (var->cnsts[i].constraint == cnst)
 237       break;
 238
 239   if (i < var->cnsts_number)
 240     var->cnsts[i].value += value;
 241   else
 242     lmm_expand(sys, cnst, var, value);
 243 }
 244
 245 void lmm_elem_set_value(lmm_system_t sys, lmm_constraint_t cnst,
 246                         lmm_variable_t var, double value)
 247 {
 248   int i;
 249
 250   for (i = 0; i < var->cnsts_number; i++)
 251     if (var->cnsts[i].constraint == cnst)
 252       break;
 253
 254   if (i < var->cnsts_number) {
 255     var->cnsts[i].value = value;
 256     sys->modified = 1;
 257   } else
 258     DIE_IMPOSSIBLE;
 259 }
 260
 261 lmm_constraint_t lmm_get_cnst_from_var(lmm_system_t sys,
 262                                        lmm_variable_t var, int num)
 263 {
 264   if (num < var->cnsts_number)
 265     return (var->cnsts[num].constraint);
 266   else
 267     return NULL;
 268 }
 269
 270 int lmm_get_number_of_cnst_from_var(lmm_system_t sys, lmm_variable_t var)
 271 {
 272   return (var->cnsts_number);
 273 }
 274
 275 lmm_variable_t lmm_get_var_from_cnst(lmm_system_t sys,
 276                                      lmm_constraint_t cnst,
 277                                      lmm_variable_t * var)
 278 {
 279   if (!(*var))
 280     xbt_swag_getFirst(&(cnst->element_set));
 281   else
 282     *var = xbt_swag_getNext(*var, cnst->element_set.offset);
 283   return *var;
 284 }
 285
 286 void *lmm_constraint_id(lmm_constraint_t cnst)
 287 {
 288   return cnst->id;
 289 }
 290
 291 void *lmm_variable_id(lmm_variable_t var)
 292 {
 293   return var->id;
 294 }
 295
 296 static void saturated_constraint_set_update(lmm_system_t sys,
 297                                             lmm_constraint_t cnst,
 298                                             double *min_usage)
 299 {
 300   lmm_constraint_t useless_cnst = NULL;
 301
 302   XBT_IN3("sys=%p, cnst=%p, min_usage=%f", sys, cnst, *min_usage);
 303   if (cnst->usage <= 0) {
 304     XBT_OUT;
 305     return;
 306   }
 307   if (cnst->remaining <= 0) {
 308     XBT_OUT;
 309     return;
 310   }
 311   if ((*min_usage < 0) || (*min_usage > cnst->remaining / cnst->usage)) {
 312     *min_usage = cnst->remaining / cnst->usage;
 313     LOG3(xbt_log_priority_trace,
 314          "min_usage=%f (cnst->remaining=%f, cnst->usage=%f)", *min_usage,
 315          cnst->remaining, cnst->usage);
 316     while ((useless_cnst =
 317             xbt_swag_getFirst(&(sys->saturated_constraint_set))))
 318       xbt_swag_remove(useless_cnst, &(sys->saturated_constraint_set));
 319
 320     xbt_swag_insert(cnst, &(sys->saturated_constraint_set));
 321   } else if (*min_usage == cnst->remaining / cnst->usage) {
 322     xbt_swag_insert(cnst, &(sys->saturated_constraint_set));
 323   }
 324   XBT_OUT;
 325 }
 326
 327 static void saturated_variable_set_update(lmm_system_t sys)
 328 {
 329   lmm_constraint_t cnst = NULL;
 330   xbt_swag_t cnst_list = NULL;
 331   lmm_element_t elem = NULL;
 332   xbt_swag_t elem_list = NULL;
 333
 334   cnst_list = &(sys->saturated_constraint_set);
 335   while ((cnst = xbt_swag_getFirst(cnst_list))) {
 336     elem_list = &(cnst->active_element_set);
 337     xbt_swag_foreach(elem, elem_list) {
 338       if (elem->variable->weight <= 0)
 339         break;
 340       if ((elem->value > 0))
 341         xbt_swag_insert(elem->variable, &(sys->saturated_variable_set));
 342     }
 343     xbt_swag_remove(cnst, cnst_list);
 344   }
 345 }
 346
 347 void lmm_print(lmm_system_t sys)
 348 {
 349   lmm_constraint_t cnst = NULL;
 350   lmm_element_t elem = NULL;
 351   lmm_variable_t var = NULL;
 352   xbt_swag_t cnst_list = NULL;
 353   xbt_swag_t var_list = NULL;
 354   xbt_swag_t elem_list = NULL;
 355   char print_buf[1024];
 356   char *trace_buf = xbt_malloc0(sizeof(char));
 357   double sum = 0.0;
 358
 359   /* Printing Objective */
 360   var_list = &(sys->variable_set);
 361   sprintf(print_buf, "MAX-MIN ( ");
 362   trace_buf =
 363       xbt_realloc(trace_buf, strlen(trace_buf) + strlen(print_buf) + 1);
 364   strcat(trace_buf, print_buf);
 365   xbt_swag_foreach(var, var_list) {
 366     sprintf(print_buf, "'%p'(%f) ", var, var->weight);
 367     trace_buf =
 368         xbt_realloc(trace_buf, strlen(trace_buf) + strlen(print_buf) + 1);
 369     strcat(trace_buf, print_buf);
 370   }
 371   sprintf(print_buf, ")");
 372   trace_buf =
 373       xbt_realloc(trace_buf, strlen(trace_buf) + strlen(print_buf) + 1);
 374   strcat(trace_buf, print_buf);
 375   DEBUG1("%s", trace_buf);
 376   trace_buf[0] = '\000';
 377
 378   DEBUG0("Constraints");
 379   /* Printing Constraints */
 380   cnst_list = &(sys->active_constraint_set);
 381   xbt_swag_foreach(cnst, cnst_list) {
 382     sum = 0.0;
 383     elem_list = &(cnst->element_set);
 384     sprintf(print_buf, "\t");
 385     trace_buf =
 386         xbt_realloc(trace_buf, strlen(trace_buf) + strlen(print_buf) + 1);
 387     strcat(trace_buf, print_buf);
 388     xbt_swag_foreach(elem, elem_list) {
 389       sprintf(print_buf, "%f.'%p'(%f) + ", elem->value,
 390               elem->variable, elem->variable->value);
 391       trace_buf =
 392           xbt_realloc(trace_buf,
 393                       strlen(trace_buf) + strlen(print_buf) + 1);
 394       strcat(trace_buf, print_buf);
 395       sum += elem->value * elem->variable->value;
 396     }
 397     sprintf(print_buf, "0 <= %f ('%p')", cnst->bound, cnst);
 398     trace_buf =
 399         xbt_realloc(trace_buf, strlen(trace_buf) + strlen(print_buf) + 1);
 400     strcat(trace_buf, print_buf);
 401
 402     if (!cnst->shared) {
 403       sprintf(print_buf, " [MAX-Constraint]");
 404       trace_buf =
 405           xbt_realloc(trace_buf,
 406                       strlen(trace_buf) + strlen(print_buf) + 1);
 407       strcat(trace_buf, print_buf);
 408     }
 409     DEBUG1("%s", trace_buf);
 410     trace_buf[0] = '\000';
 411     if (double_positive(sum - cnst->bound))
 412       WARN3("Incorrect value (%f is not smaller than %f): %g",
 413             sum, cnst->bound, sum - cnst->bound);
 414   }
 415
 416   DEBUG0("Variables");
 417   /* Printing Result */
 418   xbt_swag_foreach(var, var_list) {
 419     if (var->bound > 0) {
 420       DEBUG4("'%p'(%f) : %f (<=%f)", var, var->weight, var->value,
 421              var->bound);
 422       if (double_positive(var->value - var->bound))
 423         WARN2("Incorrect value (%f is not smaller than %f",
 424               var->value, var->bound);
 425     } else
 426       DEBUG3("'%p'(%f) : %f", var, var->weight, var->value);
 427   }
 428
 429   free(trace_buf);
 430 }
 431
 432 void lmm_solve(lmm_system_t sys)
 433 {
 434   lmm_variable_t var = NULL;
 435   lmm_constraint_t cnst = NULL;
 436   lmm_element_t elem = NULL;
 437   xbt_swag_t cnst_list = NULL;
 438   xbt_swag_t var_list = NULL;
 439   xbt_swag_t elem_list = NULL;
 440   double min_usage = -1;
 441
 442   if (!(sys->modified))
 443     return;
 444
 445   /* Init */
 446   var_list = &(sys->variable_set);
 447   DEBUG1("Variable set : %d", xbt_swag_size(var_list));
 448   xbt_swag_foreach(var, var_list) {
 449     int nb=0;
 450     int i;
 451     var->value = 0.0;
 452     for (i = 0; i < var->cnsts_number; i++) {
 453       if(var->cnsts[i].value==0.0) nb++;
 454     }
 455     if((nb==var->cnsts_number) && (var->weight>0.0))
 456       var->value = 1.0;
 457   }
 458
 459   /*
 460    * Compute Usage and store the variables that reach the maximum.
 461    */
 462   cnst_list = &(sys->active_constraint_set);
 463   DEBUG1("Active constraints : %d", xbt_swag_size(cnst_list));
 464   xbt_swag_foreach(cnst, cnst_list) {
 465     /* INIT */
 466     cnst->remaining = cnst->bound;
 467     cnst->usage = 0;
 468     elem_list = &(cnst->element_set);
 469     cnst->usage = 0.0;
 470     xbt_swag_foreach(elem, elem_list) {
 471       if (elem->variable->weight <= 0)
 472         break;
 473       if ((elem->value > 0)) {
 474         if (cnst->shared)
 475           cnst->usage += elem->value / elem->variable->weight;
 476         else if (cnst->usage < elem->value / elem->variable->weight)
 477           cnst->usage = elem->value / elem->variable->weight;
 478         DEBUG2("Constraint Usage %p : %f", cnst, cnst->usage);
 479         make_elem_active(elem);
 480       }
 481     }
 482     /* Saturated constraints update */
 483     saturated_constraint_set_update(sys, cnst, &min_usage);
 484   }
 485   saturated_variable_set_update(sys);
 486
 487   /* Saturated variables update */
 488
 489   do {
 490     /* Fix the variables that have to be */
 491     var_list = &(sys->saturated_variable_set);
 492
 493     xbt_swag_foreach(var, var_list) {
 494       /* First check if some of these variables have reach their upper
 495          bound and update min_usage accordingly. */
 496       DEBUG5
 497           ("var=%p, var->bound=%f, var->weight=%f, min_usage=%f, var->bound*var->weight=%f",
 498            var, var->bound, var->weight, min_usage,
 499            var->bound * var->weight);
 500       if ((var->bound > 0) && (var->bound * var->weight < min_usage)) {
 501         min_usage = var->bound * var->weight;
 502         DEBUG1("Updated min_usage=%f", min_usage);
 503       }
 504     }
 505
 506
 507     while ((var = xbt_swag_getFirst(var_list))) {
 508       int i;
 509
 510       var->value = min_usage / var->weight;
 511       DEBUG5("Min usage: %f, Var(%p)->weight: %f, Var(%p)->value: %f ",
 512              min_usage, var, var->weight, var, var->value);
 513
 514
 515       /* Update usage */
 516
 517       for (i = 0; i < var->cnsts_number; i++) {
 518         elem = &var->cnsts[i];
 519         cnst = elem->constraint;
 520         if (cnst->shared) {
 521           double_update(&(cnst->remaining), elem->value * var->value);
 522           double_update(&(cnst->usage), elem->value / var->weight);
 523           make_elem_inactive(elem);
 524         } else {                /* FIXME one day: We recompute usage.... :( */
 525           cnst->usage = 0.0;
 526           make_elem_inactive(elem);
 527           xbt_swag_foreach(elem, elem_list) {
 528             if (elem->variable->weight <= 0)
 529               break;
 530             if (elem->variable->value > 0)
 531               break;
 532             if ((elem->value > 0)) {
 533               if (cnst->usage < elem->value / elem->variable->weight)
 534                 cnst->usage = elem->value / elem->variable->weight;
 535               DEBUG2("Constraint Usage %p : %f", cnst, cnst->usage);
 536               make_elem_active(elem);
 537             }
 538           }
 539         }
 540       }
 541       xbt_swag_remove(var, var_list);
 542     }
 543
 544     /* Find out which variables reach the maximum */
 545     cnst_list = &(sys->active_constraint_set);
 546     min_usage = -1;
 547     xbt_swag_foreach(cnst, cnst_list) {
 548       saturated_constraint_set_update(sys, cnst, &min_usage);
 549     }
 550     saturated_variable_set_update(sys);
 551
 552   } while (xbt_swag_size(&(sys->saturated_variable_set)));
 553
 554   sys->modified = 0;
 555   if (XBT_LOG_ISENABLED(surf_maxmin, xbt_log_priority_debug)) {
 556     lmm_print(sys);
 557   }
 558 }
 559
 560 /* Not a O(1) function */
 561
 562 void lmm_update(lmm_system_t sys, lmm_constraint_t cnst,
 563                 lmm_variable_t var, double value)
 564 {
 565   int i;
 566
 567   sys->modified = 1;
 568   for (i = 0; i < var->cnsts_number; i++)
 569     if (var->cnsts[i].constraint == cnst) {
 570       var->cnsts[i].value = value;
 571       return;
 572     }
 573 }
 574
 575 /** \brief Attribute the value bound to var->bound.
 576  *
 577  *  \param sys the lmm_system_t
 578  *  \param var the lmm_variable_t
 579  *  \param bound the new bound to associate with var
 580  *
 581  *  Makes var->bound equal to bound. Whenever this function is called
 582  *  a change is  signed in the system. To
 583  *  avoid false system changing detection it is a good idea to test
 584  *  (bound != 0) before calling it.
 585  *
 586  */
 587 void lmm_update_variable_bound(lmm_system_t sys, lmm_variable_t var,
 588                                double bound)
 589 {
 590   sys->modified = 1;
 591   var->bound = bound;
 592 }
 593
 594 /** \brief Add the value delta to var->df (the sum of latencies).
 595  *
 596  *  \param sys the lmm_system_t associated
 597  *  \param var the lmm_variable_t which need to updated
 598  *  \param delta the variation of the latency
 599  *
 600  *  Add the value delta to var->df (the sum of latencys associated to the
 601  *  flow). Whenever this function is called a change is  signed in the system. To
 602  *  avoid false system changing detection it is a good idea to test
 603  *  (delta != 0) before calling it.
 604  *
 605  */
 606 void lmm_update_variable_latency(lmm_system_t sys, lmm_variable_t var,
 607                                  double delta)
 608 {
 609   sys->modified = 1;
 610   var->df += delta;
 611 }
 612
 613 void lmm_update_variable_weight(lmm_system_t sys, lmm_variable_t var,
 614                                 double weight)
 615 {
 616   int i;
 617   lmm_element_t elem;
 618
 619   XBT_IN3("(sys=%p, var=%p, weight=%f)", sys, var, weight);
 620   sys->modified = 1;
 621   var->weight = weight;
 622   xbt_swag_remove(var, &(sys->variable_set));
 623   if (weight)
 624     xbt_swag_insert_at_head(var, &(sys->variable_set));
 625   else
 626     xbt_swag_insert_at_tail(var, &(sys->variable_set));
 627
 628   for (i = 0; i < var->cnsts_number; i++) {
 629     elem = &var->cnsts[i];
 630     xbt_swag_remove(elem, &(elem->constraint->element_set));
 631     if (weight)
 632       xbt_swag_insert_at_head(elem, &(elem->constraint->element_set));
 633     else
 634       xbt_swag_insert_at_tail(elem, &(elem->constraint->element_set));
 635   }
 636   XBT_OUT;
 637 }
 638
 639 double lmm_get_variable_weight(lmm_variable_t var)
 640 {
 641   return var->weight;
 642 }
 643
 644 void lmm_update_constraint_bound(lmm_system_t sys, lmm_constraint_t cnst,
 645                                  double bound)
 646 {
 647   sys->modified = 1;
 648   cnst->bound = bound;
 649 }
 650
 651 int lmm_constraint_used(lmm_system_t sys, lmm_constraint_t cnst)
 652 {
 653   return xbt_swag_belongs(cnst, &(sys->active_constraint_set));
 654 }
 655
 656 lmm_constraint_t lmm_get_first_active_constraint(lmm_system_t sys)
 657 {
 658   return xbt_swag_getFirst(&(sys->active_constraint_set));
 659 }
 660
 661 lmm_constraint_t lmm_get_next_active_constraint(lmm_system_t sys,
 662                                                 lmm_constraint_t cnst)
 663 {
 664   return xbt_swag_getNext(cnst, (sys->active_constraint_set).offset);
 665 }