FREQUENCIES: Fix corner case for histogram calculation.

calc_stats() assumes that ft->n_valid is nonzero.  It has two callers, but
only one of them was checking ft->valid.  The other one (which produces a
histogram) is fixed up by this commit.

Found by Clang (http://clang-analyzer.llvm.org).

diff --git a/src/language/stats/frequencies.q b/src/language/stats/frequencies.q
index e52aaf0f9ae3f50d7b40880050e18b6d06170c34..d00c90c9072b6ff25f3bea65553dc534688c0f08 100644 (file)
--- a/src/language/stats/frequencies.q
+++ b/src/language/stats/frequencies.q
@@ -1,5 +1,5 @@
 /* PSPP - a program for statistical analysis.
-   Copyright (C) 1997-9, 2000, 2007, 2009 Free Software Foundation, Inc.
+   Copyright (C) 1997-9, 2000, 2007, 2009, 2010 Free Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -601,7 +601,7 @@ postcalc (const struct dataset *ds)
 
 
 
-      if ( chart == GFT_HIST && var_is_numeric (v) )
+      if ( chart == GFT_HIST && var_is_numeric (v) && ft->n_valid > 0)
        {
          double d[frq_n_stats];
          struct histogram *hist ;
@@ -1170,6 +1170,8 @@ calc_stats (const struct variable *v, double d[frq_n_stats])
 
   /* Calculate percentiles. */
 
+  assert (ft->n_valid > 0);
+
   for (i = 0; i < n_percentiles; i++)
     {
       percentiles[i].flag = 0;