Index: minmax_source.c
===================================================================
RCS file: /cvs/gsl/gsl/statistics/minmax_source.c,v
retrieving revision 1.7
diff -u -r1.7 minmax_source.c
--- minmax_source.c	26 Jun 2005 13:27:11 -0000	1.7
+++ minmax_source.c	23 Dec 2005 08:05:18 -0000
@@ -57,18 +57,68 @@
 FUNCTION(gsl_stats,minmax) (BASE * min_out, BASE * max_out, const BASE data[], const size_t stride, const size_t n)
 {
   /* finds the smallest and largest members of a dataset */
+  /* cf. Cormen et al. 2001, pp. 184--185 */
 
-  BASE min = data[0 * stride];
-  BASE max = data[0 * stride];
   size_t i;
+  BASE min;
+  BASE max;
 
-  for (i = 0; i < n; i++)
+  if (n == 0)
     {
-      if (data[i * stride] < min)
-        min = data[i * stride];
-      if (data[i * stride] > max)
-        max = data[i * stride];
+      /* We could raise an error, e.g. */
+      /*   GSL_ERROR ("length n of dataset is zero", GSL_EINVAL); */
+      /* but only if the return type of the function is changed. */
+      return;
+    }
+
+  if (n & 1) /* n is odd */
+    {
+      /* assert (n >= 1) */
+      i = 1;
+      min = data[0];
+      max = data[0];
+    }
+  else /* n is even */
+    {
+      BASE x = data[0];
+      BASE y = data[stride];
+
+      /* assert (n >= 2); */
+      i = 2;
+
+      if (x < y)
+	{
+	  min = x;
+	  max = y;
+	}
+      else
+	{
+	  min = y;
+	  max = x;
+	}
+    }
+
+  for (/*empty*/; i < n; i+=2)
+    {
+      BASE x = data[i * stride];
+      BASE y = data[(i+1) * stride];
+
+      if (x < y)
+	{
+	  if (x < min)
+	    min = x;
+	  if (y > max)
+	    max = y;
+	}
+      else
+	{
+	  if (y < min)
+	    min = y;
+	  if (x > max)
+	    max = x;
+	}
     }
+  /* assert (i == n); */
 
   *min_out = min ;
   *max_out = max ;