From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Sun, 9 Mar 2014 11:37:14 +0000 (+0000)
Subject: {n,m}_max_frags: fix fencepost efficiency problem
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?a=commitdiff_plain;ds=sidebyside;h=5d8f0782034b510b146a1b93d8f0c8f303eeb811;p=matchsticks-search.git

{n,m}_max_frags: fix fencepost efficiency problem

fixes the bug discovered/exacerbated in 41013cb05383
---

diff --git a/main.c b/main.c
index de880e9..11bdf0f 100644
--- a/main.c
+++ b/main.c
@@ -119,8 +119,18 @@ static void progress_eol(void) {
 
 static void set_best(double new_best) {
   best = new_best;
-  n_max_frags = floor(n / best);
-  m_max_frags = 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 -----*/