Fix up dsets test for some platforms with different long double format (

#4114)

test/dsets.c

@@ -5877,33 +5877,51 @@ test_floattypes(hid_t file)
         if (H5Dclose(dataset) < 0)
             goto error;
     }
-#if 0
+
 #if H5_SIZEOF_LONG_DOUBLE != H5_SIZEOF_DOUBLE
     /* long double */
     {
         long double orig_data[2][5] = {
-            {(long double)1.6081706885101836e+600L, (long double)-255.3209917099448032099170994480,
-             (long double)1.2677579992621376e-610L, (long double)64568.289448797700289448797700,
-             (long double)-1.0619721778839084e-750L},
-            {(long double)2.1499497833454840991499497833454840e+560L,
+            {(long double)1.6081706885101836e+300L, (long double)-255.3209917099448032099170994480,
+             (long double)1.2677579992621376e-310L, (long double)64568.289448797700289448797700,
+             (long double)-1.0619721778839084e-310L},
+            {(long double)2.1499497833454840991499497833454840e+257L,
              (long double)6.6562295504670740996562295504670740e-3,
              (long double)-1.5747263393432150995747263393432150,
              (long double)1.0711093225222612990711093225222612,
              (long double)-9.8971679387636870998971679387636870e-1}};
         long double new_data[2][5];
+        size_t      old_precision;
 
         TESTING("    long double (setup)");
 
         /* Define user-defined quad-precision floating-point type for dataset */
         datatype  = H5Tcopy(H5T_NATIVE_LDOUBLE);
-        precision = 128;
-        if (H5Tset_precision(datatype, precision) < 0)
-            goto error;
-        if (H5Tset_fields(datatype, (size_t)127, (size_t)112, (size_t)15, (size_t)0, (size_t)112) < 0)
-            goto error;
-        offset = 0;
-        if (H5Tset_offset(datatype, offset) < 0)
+        offset    = 5;
+        precision = 123;
+        if (0 == (old_precision = H5Tget_precision(datatype)))
             goto error;
+        if (old_precision < precision) {
+            /* Increasing precision, call H5Tset_precision first */
+            if (H5Tset_precision(datatype, precision) < 0)
+                goto error;
+            /* H5Tset_precision may have changed our offset */
+            if (H5Tset_offset(datatype, offset) < 0)
+                goto error;
+            if (H5Tset_fields(datatype, (size_t)127, (size_t)112, (size_t)15, (size_t)offset, (size_t)107) <
+                0)
+                goto error;
+        }
+        else {
+            /* Decreasing precision, call H5Tset_fields first */
+            if (H5Tset_offset(datatype, offset) < 0)
+                goto error;
+            if (H5Tset_fields(datatype, (size_t)127, (size_t)112, (size_t)15, (size_t)offset, (size_t)107) <
+                0)
+                goto error;
+            if (H5Tset_precision(datatype, precision) < 0)
+                goto error;
+        }
         if (H5Tset_size(datatype, (size_t)16) < 0)
             goto error;
         if (H5Tset_ebias(datatype, (size_t)255) < 0)
@@ -5967,7 +5985,6 @@ test_floattypes(hid_t file)
         if (H5Dclose(dataset) < 0)
             goto error;
     }
-#endif
 #endif
 
     return SUCCEED;