Changeset 2315 for branches/0.6-stable/yat/statistics/Fisher.cc

Timestamp:

Aug 20, 2010, 5:51:00 AM (13 years ago)

Author:

Peter

Message:

prefer casting to double first and then multiply rather than the opposite. fixes #638

File:

• branches/0.6-stable/yat/statistics/Fisher.cc (modified) (5 diffs)

branches/0.6-stable/yat/statistics/Fisher.cc

@@ -30 +30 @@
 
 #include <algorithm>
+#include <cassert>
 
 namespace theplu {
@@ -64 +65 @@
   void Fisher::expected(double& a, double& b, double& c, double& d) const
   {
-    double N = a_+b_+c_+d_;
+    // use floting point arithmetic to avoid overflow
+    double N = static_cast<double>(a_) + static_cast<double>(b_) 
+      + static_cast<double>(c_) + static_cast<double>(d_);
     a =((a_+b_)*(a_+c_)) / N;
     b =((a_+b_)*(b_+d_)) / N;
@@ -98 +101 @@
     d_ = d;
 
-    oddsratio_=static_cast<double>(a*d)/static_cast<double>(b*c);
+    oddsratio_= (static_cast<double>(a) / static_cast<double>(b) * 
+                 static_cast<double>(d) / static_cast<double>(c) );
     return oddsratio_;
   }
@@ -118 +122 @@
       return p_value_approximative()/2.0;
     }
+    // check for overflow
+    assert(c_ <= c_+d_ && d_ <= c_+d_);
+    assert(a_ <= a_+b_ && b_ <= a_+b_);
+    assert(a_ <= a_+c_ && c_ <= a_+c_);
+
     return statistics::cdf_hypergeometric_P(c_, c_+d_, a_+b_, a_+c_);
   }
@@ -147 +156 @@
   }
 
-
 }}} // of namespace statistics, yat, and theplu