restart.c

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#include "restart.h"
#include "backtrack.h"
#include "bump.h"
#include "decide.h"
#include "internal.h"
#include "kimits.h"
#include "logging.h"
#include "print.h"
#include "reluctant.h"
#include "report.h"
 
#include <inttypes.h>
 
ABC_NAMESPACE_IMPL_START
 
bool kissat_restarting (kissat *solver) {
  KISSAT_assert (solver->unassigned);
  if (!GET_OPTION (restart))
    return false;
  if (!solver->level)
    return false;
  if (CONFLICTS < solver->limits.restart.conflicts)
    return false;
  if (solver->stable)
    return kissat_reluctant_triggered (&solver->reluctant);
  const double fast = AVERAGE (fast_glue);
  const double slow = AVERAGE (slow_glue);
  const double margin = (100.0 + GET_OPTION (restartmargin)) / 100.0;
  const double limit = margin * slow;
  kissat_extremely_verbose (solver,
                            "restart glue limit %g = "
                            "%.02f * %g (slow glue) %c %g (fast glue)",
                            limit, margin, slow,
                            (limit > fast    ? '>'
                             : limit == fast ? '='
                                             : '<'),
                            fast);
  return (limit <= fast);
}
 
void kissat_update_focused_restart_limit (kissat *solver) {
  KISSAT_assert (!solver->stable);
  limits *limits = &solver->limits;
  uint64_t restarts = solver->statistics_.restarts;
  uint64_t delta = GET_OPTION (restartint);
  if (restarts)
    delta += kissat_logn (restarts) - 1;
  limits->restart.conflicts = CONFLICTS + delta;
  kissat_extremely_verbose (solver,
                            "focused restart limit at %" PRIu64
                            " after %" PRIu64 " conflicts ",
                            limits->restart.conflicts, delta);
}
 
static unsigned reuse_stable_trail (kissat *solver) {
  const heap *const scores = SCORES;
  const unsigned next_idx = kissat_next_decision_variable (solver);
  const double limit = kissat_get_heap_score (scores, next_idx);
  unsigned level = solver->level, res = 0;
  while (res < level) {
    frame *f = &FRAME (res + 1);
    const unsigned idx = IDX (f->decision);
    const double score = kissat_get_heap_score (scores, idx);
    if (score <= limit)
      break;
    res++;
  }
  return res;
}
 
static unsigned reuse_focused_trail (kissat *solver) {
  const links *const links = solver->links;
  const unsigned next_idx = kissat_next_decision_variable (solver);
  const unsigned limit = links[next_idx].stamp;
  LOG ("next decision variable stamp %u", limit);
  unsigned level = solver->level, res = 0;
  while (res < level) {
    frame *f = &FRAME (res + 1);
    const unsigned idx = IDX (f->decision);
    const unsigned score = links[idx].stamp;
    if (score <= limit)
      break;
    res++;
  }
  return res;
}
 
static unsigned reuse_trail (kissat *solver) {
  KISSAT_assert (solver->level);
  KISSAT_assert (!EMPTY_STACK (solver->trail));
 
  if (!GET_OPTION (restartreusetrail))
    return 0;
 
  unsigned res;
 
  if (solver->stable)
    res = reuse_stable_trail (solver);
  else
    res = reuse_focused_trail (solver);
 
  LOG ("matching trail level %u", res);
 
  if (res) {
    INC (restarts_reused_trails);
    ADD (restarts_reused_levels, res);
    LOG ("restart reuses trail at decision level %u", res);
  } else
    LOG ("restarts does not reuse the trail");
 
  return res;
}
 
void kissat_restart (kissat *solver) {
  START (restart);
  INC (restarts);
  ADD (restarts_levels, solver->level);
  if (solver->stable)
    INC (stable_restarts);
  else
    INC (focused_restarts);
  unsigned level = reuse_trail (solver);
  kissat_extremely_verbose (solver,
                            "restarting after %" PRIu64 " conflicts"
                            " (limit %" PRIu64 ")",
                            CONFLICTS, solver->limits.restart.conflicts);
  LOG ("restarting to level %u", level);
  kissat_backtrack_in_consistent_state (solver, level);
  if (!solver->stable)
    kissat_update_focused_restart_limit (solver);
  REPORT (1, 'R');
  STOP (restart);
}
 
ABC_NAMESPACE_IMPL_END