Fix FTBFS on i686-linux due to rounding issue (see references).

Fixes Guix bug #22049 (see below).

Copied from Debian.

Source:
https://sources.debian.net/src/ilmbase/2.2.0-11/debian/patches/testBoxAlgo.patch/
https://sources.debian.net/src/ilmbase/2.2.0-11/debian/patches/testBox.patch/

References:
https://lists.nongnu.org/archive/html/openexr-devel/2015-12/msg00001.html
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=22049
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=815712
https://anonscm.debian.org/cgit/pkg-phototools/ilmbase.git/commit/?id=ab28bb45cdad8adc32e345b777ab8e692b1d9a9c

---

Subject: testBoxAlgo: allow fuzzy match of b12 == b2
From: Steven Chamberlain <steven@pyro.eu.org>
Date: Wed, 24 Feb 2016 01:04:11 +0000

Also fix a pre-existing typo.

--- a/IlmBase/ImathTest/testBoxAlgo.cpp
+++ b/IlmBase/ImathTest/testBoxAlgo.cpp
@@ -886,10 +886,11 @@ boxMatrixTransform ()
 
     assert (approximatelyEqual (b2.min, b4.min, e));
     assert (app</td></tr></table>
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<div class='content'><div id='summary'>te <class T>
+bool
+approximatelyEqual (const T &p1, const T &p2)
+{
+	/* int and short should be exact */
+	return (p1 == p2);
+}
+
+bool
+approximatelyEqual (const Vec2<float> &p1, const Vec2<float> &p2)
+{
+    float e = limits<float>::epsilon();
+    float m = 0;
+
+    for (int i = 0; i < 2; ++i)
+    {
+	m = max (m, abs (p1[i]));
+	m = max (m, abs (p2[i]));
+    }
+
+    for (int i = 0; i < 2; ++i)
+	if (!equalWithAbsError (p1[i], p2[i], m * e))
+	    return false;
+
+    return true;
+}
+
+bool
+approximatelyEqual (const Vec2<double> &p1, const Vec2<double> &p2)
+{
+#if defined(__i386__) || defined(_M_IX86)
+    /* double-rounding on 32-bit x86 may cause larger error:
+       use epsilon of float rather than double */
+    double e = limits<float>::epsilon();
+#else
+    double e = limits<double>::epsilon();
+#endif
+    double m = 0;
+
+    for (int i = 0; i < 2; ++i)
+    {
+	m = max (m, abs (p1[i]));
+	m = max (m, abs (p2[i]));
+    }
+
+    for (int i = 0; i < 2; ++i)
+	if (!equalWithAbsError (p1[i], p2[i], m * e))
+	    return false;
+
+    return true;
+}
+
 //
 // Test case generation utility - create a vector of IMATH_INTERNAL_NAMESPACE::Vec{2,3,4}
 // with all permutations of integers 1..T::dimensions().
@@ -250,7 +302,8 @@ testExtendByPoint(const char *type)
                               
         IMATH_INTERNAL_NAMESPACE::Box<T> b;
         b.extendBy(p);
-        assert(b.min == p && b.max == p);
+        assert (approximatelyEqual (b.min, p));
+        assert (approximatelyEqual (b.max, p));
     }
 
     //
@@ -283,7 +336,8 @@ testExtendByPoint(const char *type)
 
             b.extendBy(p);
 
-            assert(b.min == min && b.max == max);
+            assert (approximatelyEqual (b.min, min));
+            assert (approximatelyEqual (b.max, max));
         }
     }
 }
@@ -358,7 +412,8 @@ testExtendByBox(const char *type)
             }
             b.extendBy(IMATH_INTERNAL_NAMESPACE::Box<T>(p0, p1));
 
-            assert(b.min == min && b.max == max);
+            assert (approximatelyEqual (b.min, min));
+            assert (approximatelyEqual (b.max, max));
         }
     }
 }