Avoid infinity calculations in rank_cd

diff --git a/contrib/tsearch2/rank.c b/contrib/tsearch2/rank.c
index f8a7d5f2f063e97e5bb612d3097d1389b81aeb5e..7bd5e1adf01188462b4947cd911cff97413ae22d 100644 (file)
--- a/contrib/tsearch2/rank.c
+++ b/contrib/tsearch2/rank.c
@@ -667,6 +667,7 @@ calc_rank_cd(float4 *arrdata, tsvector * txt, QUERYTYPE * query, int method)
    {
        double      Cpos = 0.0;
        double      InvSum = 0.0;
+       int         nNoise;
        DocRepresentation *ptr = ext.begin;
 
        while (ptr <= ext.end)
@@ -676,7 +677,16 @@ calc_rank_cd(float4 *arrdata, tsvector * txt, QUERYTYPE * query, int method)
        }
 
        Cpos = ((double) (ext.end - ext.begin + 1)) / InvSum;
-       Wdoc += Cpos / ((double) ((1 + (ext.q - ext.p) - (ext.end - ext.begin))));
+       /*
+        * if doc are big enough then ext.q may be equal to ext.p
+        * due to limit of posional information. In this case we 
+        * approximate number of noise word as half cover's
+        * length
+        */
+       nNoise = (ext.q - ext.p) - (ext.end - ext.begin);
+       if ( nNoise < 0 )
+           nNoise = (ext.end - ext.begin) / 2;
+       Wdoc += Cpos / ((double) (1 + nNoise));
 
        CurExtPos = ((double) (ext.q + ext.p)) / 2.0;
        if (NExtent > 0 && CurExtPos > PrevExtPos       /* prevent devision by