commentary: clarify and fix input vs output confusion

[matchsticks-search.git] / main.c

diff --git a/main.c b/main.c
index d2900152f1336eaace2a8b656024f9f48dde100e..93dc7ebe5325269db8fda05f5fe954a081489ed3 100644 (file)
--- a/main.c
+++ b/main.c
@@ -58,7 +58,8 @@
  *
  * We search all possible adjacency matrices, and for each one we run
  * GLPK's simplex solver.  We represent the adjacency matrix as an
  *
  * We search all possible adjacency matrices, and for each one we run
  * GLPK's simplex solver.  We represent the adjacency matrix as an

- * array of bitmaps.
+ * array of bitmaps: one word per input stick, with one bit per output
+ * stick.

  *
  * However, there are a couple of wrinkles:
  *
  *
  * However, there are a couple of wrinkles:
  *


@@ -76,7 +77,7 @@
  * nondecreasing in array order.
  *
  * Once we have a solution, we also avoid considering any candidate
  * nondecreasing in array order.
  *
  * Once we have a solution, we also avoid considering any candidate

- * which involves dividing one of the output sticks into so many
+ * which involves dividing one of the input sticks into so many

  * fragment that the smallest fragment would necessarily be no bigger
  * than our best solution.  That is, we reject candidates where any of
  * the hamming weights of the adjacency bitmap words are too large.
  * fragment that the smallest fragment would necessarily be no bigger
  * than our best solution.  That is, we reject candidates where any of
  * the hamming weights of the adjacency bitmap words are too large.


@@ -91,6 +92,8 @@
 typedef uint32_t AdjWord;
 #define PRADJ "08"PRIx32
 
 typedef uint32_t AdjWord;
 #define PRADJ "08"PRIx32
 

+#define FOR_BITS(j,m) for (j=0, j##bit=1; j < (m); j++, j##bit<<=1)
+

 static int n, m, maxhamweight;
 static AdjWord *adjmatrix;
 static AdjWord adjall;
 static int n, m, maxhamweight;
 static AdjWord *adjmatrix;
 static AdjWord adjall;


@@ -99,7 +102,7 @@ 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;
+static int n_max_frags, m_max_frags;

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


@@ -117,7 +120,18 @@ 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);
+  /*
+   * 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 -----*/


@@ -308,10 +322,10 @@ static void multicore(void) {
 
   for (w=0; w<ncpus; w++) {
     mc_rwvsetup_full();
 
   for (w=0; w<ncpus; w++) {
     mc_rwvsetup_full();

-    LPRINTF("reading report from %2d\n",w);
+    LPRINTF("reading report from %2d",w);

     ssize_t sr = preadv(fileno(mc_workers[w].results), mc_iov, mc_niovs, 0);
     if (!sr) continue;
     ssize_t sr = preadv(fileno(mc_workers[w].results), mc_iov, mc_niovs, 0);
     if (!sr) continue;

-    LPRINTF("got report from %2d\n",w);
+    LPRINTF("got report from %2d",w);

     maxhamweight = 0;
     optimise(1);
   }
     maxhamweight = 0;
     optimise(1);
   }


@@ -353,17 +367,21 @@ 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;
+  n_max_frags = INT_MAX;
+  m_max_frags = INT_MAX;

 }
 
 }
 

+#if 0

 static AdjWord one_adj_bit(int bitnum) {
   return (AdjWord)1 << bitnum;
 }
 static AdjWord one_adj_bit(int bitnum) {
   return (AdjWord)1 << bitnum;
 }

+#endif

 
 static int count_set_adj_bits(AdjWord w) {
 
 static int count_set_adj_bits(AdjWord w) {

-  int j, total;
-  for (j=0, total=0; j<m; j++)
-    total += !!(w & one_adj_bit(j));
+  int j, total = 0;
+  AdjWord jbit;
+  FOR_BITS(j,m)
+    total += !!(w & jbit);

   return total;
 }
 
   return total;
 }
 


@@ -372,8 +390,7 @@ static int count_set_adj_bits(AdjWord w) {
 static int totalfrags;
 
 static bool maxhamweight_ok(void) {
 static int totalfrags;
 
 static bool maxhamweight_ok(void) {

-  double maxminsize = (double)m / maxhamweight;
-  return maxminsize > best;
+  return maxhamweight <= m_max_frags;

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


@@ -384,14 +401,13 @@ static bool preconsider_ok(int nwords, bool doprint) {
   bool had_max = 0;
   for (i=0, totalfrags=0; i<nwords; i++) {
     int frags = count_set_adj_bits(adjmatrix[i]);
   bool had_max = 0;
   for (i=0, totalfrags=0; i<nwords; i++) {
     int frags = count_set_adj_bits(adjmatrix[i]);

-    had_max += (frags >= maxhamweight);
-    totalfrags += frags;

     PRINTF("%"PRADJ" ", adjmatrix[i]);
     PRINTF("%"PRADJ" ", adjmatrix[i]);

-    double maxminsize = (double)m / frags;
-    if (maxminsize <= best) {
+    if (frags > m_max_frags) {

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

+    had_max += (frags >= maxhamweight);
+    totalfrags += frags;

   }
   if (!had_max) {
     /* Skip this candidate as its max hamming weight is lower than
   }
   if (!had_max) {
     /* Skip this candidate as its max hamming weight is lower than


@@ -411,6 +427,7 @@ static void optimise(bool doprint) {
   /* Consider the best answer (if any) for a given adjacency matrix */
   glp_prob *prob = 0;
   int i, j;
   /* Consider the best answer (if any) for a given adjacency matrix */
   glp_prob *prob = 0;
   int i, j;

+  AdjWord jbit;

 
   /*
    * Up to a certain point, optimise() can be restarted.  We use this
 
   /*
    * Up to a certain point, optimise() can be restarted.  We use this


@@ -496,8 +513,8 @@ static void optimise(bool doprint) {
   glp_set_obj_coef(prob, X_minimum, 1);
 
   for (i=0; i<n; i++) {
   glp_set_obj_coef(prob, X_minimum, 1);
 
   for (i=0; i<n; i++) {

-    for (j=0; j<m; j++) {
-      if (!(adjmatrix[i] & one_adj_bit(j)))
+    FOR_BITS(j,m) {
+      if (!(adjmatrix[i] & jbit))

        continue;
       /* x_total_i += x_minimum */
       /* x_total_j += x_minimum */
        continue;
       /* x_total_i += x_minimum */
       /* x_total_j += x_minimum */


@@ -598,6 +615,9 @@ static void optimise(bool doprint) {
 }
 
 static void iterate_recurse(int i, AdjWord min) {
 }
 
 static void iterate_recurse(int i, AdjWord min) {

+  int j;
+  AdjWord jbit;
+

   if (i >= n) {
     printcounter++;
     optimise(!(printcounter & 0xfff));
   if (i >= n) {
     printcounter++;
     optimise(!(printcounter & 0xfff));


@@ -615,18 +635,18 @@ static void iterate_recurse(int i, AdjWord min) {
     if (i == 0 && (adjmatrix[i] & (1+adjmatrix[i])))
       goto again;
 
     if (i == 0 && (adjmatrix[i] & (1+adjmatrix[i])))
       goto again;
 

-    for (int j = 0; j < m; j++)
-      if (adjmatrix[i] & one_adj_bit(j))
+    FOR_BITS(j,m)
+      if (adjmatrix[i] & jbit)

         weight[j]++;
     for (int j = 0; j < m; j++)
         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]);
 
   takeout:
         goto takeout;
 
     iterate_recurse(i+1, adjmatrix[i]);
 
   takeout:

-    for (int j = 0; j < m; j++)
-      if (adjmatrix[i] & one_adj_bit(j))
+    FOR_BITS(j,m)
+      if (adjmatrix[i] & jbit)

         weight[j]--;
 
   again:
         weight[j]--;
 
   again: