gib_list_randomize: use code better suited for short lists (closes #151)

Note that the i == r check was never reached in the original code but may be
in the new variant. Since a shuffled list may well have one or two elements
retain their absolute position once in a while, this should not be a problem.

tests with 2- and 3-element lists show an even distribution amongst all
elements.

2 files changed, 5 insertions, 6 deletions

diff --git a/ChangeLog b/ChangeLog
index 375a80b..0a441c9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -9,6 +9,7 @@ git HEAD
       three projects (one of which is feh). There is at least one known bug
       in it, and as I do not have the time to take over giblib development,
       importing the library seems to be the best solution.
+    * Fix/improve --randomize for short filelists (closes #151)
 
 Sun, 27 Apr 2014 20:28:02 +0200  Daniel Friesel <derf+feh@finalrewind.org>
 
diff --git a/src/gib_list.c b/src/gib_list.c
index 1c313ba..a05fb4c 100644
--- a/src/gib_list.c
+++ b/src/gib_list.c
@@ -362,12 +362,10 @@ gib_list_randomize(gib_list * list)
    srand(getpid() * time(NULL) % ((unsigned int) -1));
    for (i = 0; i < len - 1; i++)
    {
-      r = (int) ((len - i - 1) * ((float) rand()) / (RAND_MAX + 1.0)) + i + 1;
-      if (i == r)
-         abort();
-      t = farray[i];
-      farray[i] = farray[r];
-      farray[r] = t;
+      r = i + rand() / (RAND_MAX / (len - i) + 1 );
+      t = farray[r];
+      farray[r] = farray[i];
+      farray[i] = t;
    }
    list = farray[0];
    list->prev = NULL;