Fix test fails on Debian 32 bit system due to gcc bug 323

On some 32 bit platforms, there is a gcc bug that makes floating point
calculations and comparisons unstable (see the link below). The problem
originates in FPU 80 bits registers where double values are not truncated
to 64 bit values. When gcc compiles some code with enabled optimizations,
the intermediate results may be kept in the FPU registers without truncation
to 64 bit values. Extra bits may produce unstable results when comparing
the numbers.

The generic solution is to save the intermediate results in the memory where
the values are truncated to 64 bit values. It affects the performance but
makes the tests stable on all platforms.

PGSPHERE_FLOAT_STORE macro enables storing of intermediate results for FPxx
operations in the memory. It is enabled by default for 32 bit platforms.
It can be explicitly enabled or disabled in CFLAGS. To enable it for all
code the gcc option -ffloat-store may be used as well.

Link to gcc bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=323

Author: Vitaly Davydov

Diff for: src/pg_sphere.h

@@ -45,10 +45,85 @@
 
 #include "pgs_util.h"
 
+/* On some 32 bit platforms, there is a gcc bug that makes floating point
+ * calculations and comparisons unstable (see the link below). The problem
+ * originates in FPU 80 bits registers where double values are not truncated
+ * to 64 bit values. When gcc compiles some code with enabled optimizations,
+ * the intermediate results may be kept in the FPU registers without truncation
+ * to 64 bit values. Extra bits may produce unstable results when comparing
+ * the numbers.
+ *
+ * The generic solution is to save the intermediate results in the memory where
+ * the values are truncated to 64 bit values. It affects the performance but
+ * makes the tests stable on all platforms.
+ *
+ * PGSPHERE_FLOAT_STORE macro enables storing of intermediate results for FPxx
+ * operations in the memory. It is enabled by default for 32 bit platforms.
+ * It can be explicitly enabled or disabled in CFLAGS. To enable it for all
+ * code the gcc option -ffloat-store may be used as well.
+ *
+ * Link to gcc bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=323
+ */
+#if !defined(PGSPHERE_FLOAT_STORE)
+#if _WIN64 || (__GNUC__ && __x86_64__)
+#define PGSPHERE_FLOAT_STORE 0
+#elif _WIN32 || __GNUC__
+#define PGSPHERE_FLOAT_STORE 1
+#else
+#define PGSPHERE_FLOAT_STORE 0
+#endif
+#endif // PGSPHERE_FLOAT_STORE
+
 #define EPSILON					1.0E-09
 
 #define FPzero(A)				(fabs(A) <= EPSILON)
 
+#if PGSPHERE_FLOAT_STORE
+
+static inline bool
+FPeq(double A, double B)
+{
+	const volatile double AB = A - B;
+	return A == B || fabs(AB) <= EPSILON;
+}
+
+static inline bool
+FPne(double A, double B)
+{
+	const volatile double AB = A - B;
+	return A != B && fabs(AB) > EPSILON;
+}
+
+static inline bool
+FPlt(double A, double B)
+{
+	const volatile double AE = A + EPSILON;
+	return AE < B;
+}
+
+static inline bool
+FPle(double A, double B)
+{
+	const volatile double BE = B + EPSILON;
+	return A <= BE;
+}
+
+static inline bool
+FPgt(double A, double B)
+{
+	const volatile double BE = B + EPSILON;
+	return A > BE;
+}
+
+static inline bool
+FPge(double A, double B)
+{
+	const volatile double AE = A + EPSILON;
+	return AE >= B;
+}
+
+#else
+
 static inline bool
 FPeq(double A, double B)
 {
@@ -85,6 +160,8 @@ FPge(double A, double B)
 	return A + EPSILON >= B;
 }
 
+#endif // PGSPHERE_FLOAT_STORE
+
 /*---------------------------------------------------------------------
  * Point - (x,y)
  *-------------------------------------------------------------------*/