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Miscellaneous fixes. Correct a comparison of y with w causing
assertion failures in portrait-type grids; retire an unused array in
the game generation function (my original generation strategy needed
it, but the final one didn't); correct a typo; further restrict the
generable sizes of game and include a special case for 4x4dt to
prevent a tight loop.

[originally from svn r6405]

--- a/tents.c

+++ b/tents.c

@@ -415,8 +415,12 @@

 static char *validate_params(game_params *params, int full)

 {

-    if (params->w < 2 || params->h < 2)

-	return "Width and height must both be at least two";

+    /*

+     * Generating anything under 4x4 runs into trouble of one kind

+     * or another.

+     */

+    if (params->w < 4 || params->h < 4)

+	return "Width and height must both be at least four";

     return NULL;

 }

@@ -916,7 +920,7 @@

     char *puzzle = snewn(w*h, char);

     int *numbers = snewn(w+h, int);

     char *soln = snewn(w*h, char);

-    int *temp = snewn(2*w*h, int), *itemp = temp + w*h;

+    int *temp = snewn(2*w*h, int);

     int maxedges = ntrees*4 + w*h;

     int *edges = snewn(2*maxedges, int);

     int *capacity = snewn(maxedges, int);

@@ -962,9 +966,9 @@

      * The maxflow algorithm is not randomised, so employed naively

      * it would give rise to grids with clear structure and

      * directional bias. Hence, I assign the network nodes as seen

-     * by maxflow to be a _random_ permutation the squares of the

-     * grid, so that any bias shown by maxflow towards low-numbered

-     * nodes is turned into a random bias.

+     * by maxflow to be a _random_ permutation of the squares of

+     * the grid, so that any bias shown by maxflow towards

+     * low-numbered nodes is turned into a random bias.

      * 

      * This generation strategy can fail at many points, including

      * as early as tent placement (if you get a bad random order in

@@ -979,16 +983,16 @@

      * trouble.

      */

+    if (params->diff > DIFF_EASY && params->w <= 4 && params->h <= 4)

+	params->diff = DIFF_EASY;      /* downgrade to prevent tight loop */

+

     while (1) {

 	/*

-	 * Arrange the grid squares into a random order, and invert

-	 * that order so we can find a square's index as well.

+	 * Arrange the grid squares into a random order.

 	 */

 	for (i = 0; i < w*h; i++)

 	    temp[i] = i;

 	shuffle(temp, w*h, sizeof(*temp), rs);

-	for (i = 0; i < w*h; i++)

-	    itemp[temp[i]] = i;

 	/*

 	 * The first `ntrees' entries in temp which we can get

@@ -1562,7 +1566,7 @@

         ymin = min(ui->dsy, ui->dey);

         ymax = max(ui->dsy, ui->dey);

         assert(0 <= xmin && xmin <= xmax && xmax < w);

-        assert(0 <= ymin && ymin <= ymax && ymax < w);

+        assert(0 <= ymin && ymin <= ymax && ymax < h);

         buflen = 0;

         bufsize = 256;