From c1389c006df5a84381565bc893787b0f79a52de9 Mon Sep 17 00:00:00 2001
From: Sylvain Pion <Sylvain.Pion@sophia.inria.fr>
Date: Tue, 12 Aug 2008 12:43:20 +0000
Subject: [PATCH] Add a couple of handy functions:   bool are_sorted(const T &
 a, const T & b, const T & c)   bool are_strictly_sorted(const T & a, const T
 & b, const T & c)   bool are_ordered(const T & a, const T & b, const T & c)  
 bool are_strictly_ordered(const T & a, const T & b, const T & c)

---
 .../include/CGAL/predicates/kernel_ftC2.h     |  7 ++--
 STL_Extension/include/CGAL/algorithm.h        | 40 ++++++++++++++++++-
 2 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/Cartesian_kernel/include/CGAL/predicates/kernel_ftC2.h b/Cartesian_kernel/include/CGAL/predicates/kernel_ftC2.h
index f17c69f3af0..a9f79fd092c 100644
--- a/Cartesian_kernel/include/CGAL/predicates/kernel_ftC2.h
+++ b/Cartesian_kernel/include/CGAL/predicates/kernel_ftC2.h
@@ -25,6 +25,7 @@
 #ifndef CGAL_PREDICATES_KERNEL_FTC2_H
 #define CGAL_PREDICATES_KERNEL_FTC2_H
 
+#include <CGAL/algorithm.h>
 #include <CGAL/number_utils.h>
 #include <CGAL/predicates/sign_of_determinant.h>
 #include <CGAL/constructions/kernel_ftC2.h>
@@ -195,7 +196,7 @@ compare_y_at_xC2(const FT &px, const FT &py,
     // compares the y-coordinates of p and the vertical projection of p on s.
     // Precondition : p is in the x-range of s.
 
-    CGAL_kernel_precondition(px >= (CGAL::min)(ssx, stx) && px <= (CGAL::max)(ssx, stx));
+    CGAL_kernel_precondition(are_ordered(ssx, px, stx));
 
     if (ssx < stx)
 	return orientationC2(px, py, ssx, ssy, stx, sty);
@@ -225,8 +226,8 @@ compare_y_at_x_segment_C2(const FT &px,
     //   - if the segments intersect, return EQUAL
     //   - if not, return the obvious SMALLER/LARGER.
 
-    CGAL_kernel_precondition(px >= (CGAL::min)(s1sx, s1tx) && px <= (CGAL::max)(s1sx, s1tx));
-    CGAL_kernel_precondition(px >= (CGAL::min)(s2sx, s2tx) && px <= (CGAL::max)(s2sx, s2tx));
+    CGAL_kernel_precondition(are_ordered(s1sx, px, s1tx));
+    CGAL_kernel_precondition(are_ordered(s2sx, px, s2tx));
 
     if (s1sx != s1tx && s2sx != s2tx) {
 	FT s1stx = s1sx-s1tx;
diff --git a/STL_Extension/include/CGAL/algorithm.h b/STL_Extension/include/CGAL/algorithm.h
index 135d2e9fd80..1ed3d2568f1 100644
--- a/STL_Extension/include/CGAL/algorithm.h
+++ b/STL_Extension/include/CGAL/algorithm.h
@@ -29,11 +29,49 @@
 #include <CGAL/basic.h>
 #include <CGAL/copy_n.h>
 #include <algorithm>
-
 #include <iosfwd>
 
 CGAL_BEGIN_NAMESPACE
 
+// Not documented
+template <class T> inline
+bool
+are_sorted(const T & a, const T & b, const T & c)
+{
+  return a <= b && b <= c;
+}
+
+// Not documented
+template <class T> inline
+bool
+are_strictly_sorted(const T & a, const T & b, const T & c)
+{
+  return a < b && b < c;
+}
+
+// Not documented
+// Checks that b is in the interval [min(a, c) , max(a, c)].
+template <class T> inline
+bool
+are_ordered(const T & a, const T & b, const T & c)
+{
+  const T& min = (CGAL::min)(a, c);
+  const T& max = (CGAL::max)(a, c);
+  return min <= b && b <= max;
+}
+
+// Not documented
+// Checks that b is in the interval ]min(a, c) , max(a, c)[.
+template <class T> inline
+bool
+are_strictly_ordered(const T & a, const T & b, const T & c)
+{
+  const T& min = (CGAL::min)(a, c);
+  const T& max = (CGAL::max)(a, c);
+  return min < b && b < max;
+}
+
+
 template <class ForwardIterator>
 inline
 ForwardIterator