{n,m}_max_frags: fix fencepost efficiency problem

[matchsticks-search.git] / main.c

diff --git a/main.c b/main.c
index 69f56d1a30e8bba421e9e7a7231019a45f08b09d..11bdf0fba64e7605e11e54511142be5d20bbf689 100644 (file)
--- a/main.c
+++ b/main.c
@@ -101,7 +101,7 @@ static double best;
 static glp_prob *best_prob;
 static AdjWord *best_adjmatrix;
 
 static glp_prob *best_prob;
 static AdjWord *best_adjmatrix;
 

-static int n_over_best, m_over_best;
+static int n_max_frags, m_max_frags;

 static int *weight;
 
 static unsigned printcounter;
 static int *weight;
 
 static unsigned printcounter;


@@ -119,8 +119,18 @@ static void progress_eol(void) {
 
 static void set_best(double new_best) {
   best = new_best;
 
 static void set_best(double new_best) {
   best = new_best;

-  n_over_best = floor(n / best);
-  m_over_best = floor(m / best);
+  /*
+   * When computing n_max_frags, we want to set a value that will skip
+   * anything that won't provide strictly better solutions.  So we
+   * want
+   *             frags <      n / best
+   *                        _          _
+   *   <=>       frags <   |  n / best  |
+   *                        _          _
+   *   <=>       frags <=  |  n / best  | - 1
+   */
+  n_max_frags = ceil(n / best) - 1;
+  m_max_frags = ceil(m / best) - 1;

 }
 
 /*----- multicore support -----*/
 }
 
 /*----- multicore support -----*/


@@ -356,8 +366,8 @@ static void prep(void) {
   glp_term_out(GLP_OFF);
   setlinebuf(stderr);
   weight = calloc(sizeof(*weight), m);  assert(weight);
   glp_term_out(GLP_OFF);
   setlinebuf(stderr);
   weight = calloc(sizeof(*weight), m);  assert(weight);

-  n_over_best = INT_MAX;
-  m_over_best = INT_MAX;
+  n_max_frags = INT_MAX;
+  m_max_frags = INT_MAX;

 }
 
 #if 0
 }
 
 #if 0


@@ -379,7 +389,7 @@ static int count_set_adj_bits(AdjWord w) {
 static int totalfrags;
 
 static bool maxhamweight_ok(void) {
 static int totalfrags;
 
 static bool maxhamweight_ok(void) {

-  return maxhamweight <= m_over_best;
+  return maxhamweight <= m_max_frags;

 }
 
 static bool preconsider_ok(int nwords, bool doprint) {
 }
 
 static bool preconsider_ok(int nwords, bool doprint) {


@@ -391,7 +401,7 @@ static bool preconsider_ok(int nwords, bool doprint) {
   for (i=0, totalfrags=0; i<nwords; i++) {
     int frags = count_set_adj_bits(adjmatrix[i]);
     PRINTF("%"PRADJ" ", adjmatrix[i]);
   for (i=0, totalfrags=0; i<nwords; i++) {
     int frags = count_set_adj_bits(adjmatrix[i]);
     PRINTF("%"PRADJ" ", adjmatrix[i]);

-    if (frags > m_over_best) {
+    if (frags > m_max_frags) {

       PRINTF(" too fine");
       goto out;
     }
       PRINTF(" too fine");
       goto out;
     }


@@ -628,7 +638,7 @@ static void iterate_recurse(int i, AdjWord min) {
       if (adjmatrix[i] & jbit)
         weight[j]++;
     for (int j = 0; j < m; j++)
       if (adjmatrix[i] & jbit)
         weight[j]++;
     for (int j = 0; j < m; j++)

-      if (weight[j] >= n_over_best)
+      if (weight[j] >= n_max_frags)

         goto takeout;
 
     iterate_recurse(i+1, adjmatrix[i]);
         goto takeout;
 
     iterate_recurse(i+1, adjmatrix[i]);