Reduce number of multiplications for higher moments.

[pspp-builds.git] / src / math / moments.c

diff --git a/src/math/moments.c b/src/math/moments.c
index ce2f825c8e0156cc0e3d27dca54415da74512906..17040e9f699335fe91021cb5331ce1f257574ef5 100644 (file)
--- a/src/math/moments.c
+++ b/src/math/moments.c
@@ -1,6 +1,5 @@
 /* PSPP - computes sample statistics.
    Copyright (C) 1997-9, 2000 Free Software Foundation, Inc.
-   Written by Ben Pfaff <blp@gnu.org>.
 
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License as
@@ -22,9 +21,9 @@
 #include <assert.h>
 #include <math.h>
 #include <stdlib.h>
-#include "alloc.h"
-#include "misc.h"
-#include "value.h"
+#include <libpspp/alloc.h>
+#include <libpspp/misc.h>
+#include <data/value.h>
 
 #include "gettext.h"
 #define _(msgid) gettext (msgid)
@@ -44,11 +43,7 @@ calc_moments (enum moment max_moment,
 
   if (max_moment >= MOMENT_VARIANCE && w > 1.) 
     {
-      double s2;
-
-      /* From _Numerical Recipes in C_, 2nd ed., 0-521-43108-5,
-         section 14.1. */
-      s2 = (d2 - pow2 (d1) / w) / (w - 1.);
+      double s2 = (d2 - pow2 (d1) / w) / (w - 1.);
       if (variance != NULL)
         *variance = s2;
 
@@ -156,8 +151,6 @@ moments_pass_one (struct moments *m, double value, double weight)
 void
 moments_pass_two (struct moments *m, double value, double weight) 
 {
-  double d, d_power;
-
   assert (m != NULL);
 
   if (m->pass == 1) 
@@ -169,28 +162,25 @@ moments_pass_two (struct moments *m, double value, double weight)
 
   if (value != SYSMIS && weight >= 0.) 
     {
-      m->w2 += weight;
-
-      d = d_power = value - m->mean;
-      m->d1 += d_power * weight;
-
+      double d = value - m->mean;
+      double d1_delta = d * weight;
+      m->d1 += d1_delta;
       if (m->max_moment >= MOMENT_VARIANCE) 
         {
-          d_power *= d;
-          m->d2 += d_power * weight;
-
+          double d2_delta = d1_delta * d;
+          m->d2 += d2_delta;
           if (m->max_moment >= MOMENT_SKEWNESS)
             {
-              d_power *= d;
-              m->d3 += d_power * weight;
-
+              double d3_delta = d2_delta * d;
+              m->d3 += d3_delta;
               if (m->max_moment >= MOMENT_KURTOSIS)
                 {
-                  d_power *= d;
-                  m->d4 += d_power * weight;
+                  double d4_delta = d3_delta * d;
+                  m->d4 += d4_delta;
                 }
             }
         }
+      m->w2 += weight;
     }
 }