H5Ztrans: (feature) Improved H5Z_xform_noop() and H5Z_xform_create() … (

#933)

* H5Ztrans: (feature) Improved H5Z_xform_noop() and H5Z_xform_create() function

- Made a small improvement for H5Z_xform_noop() function. Now,
  the function will also return TRUE if the data transform function
  expression = "x". For this case, the HDF5 library behaves in a
  similar fashion as the case when no data transform function has been
  specified.
- Improved the inline documentation of the function
  H5Z_xform_create() such it is more inline with the rest of the
  code.

* Committing clang-format changes

* H5Ztrans: (feature) Added 3 tests for improved H5Z_xform_noop() function

- Added serial test with data transform expression = "x" to
  verify the improved H5Z_xform_noop() function behaves as expected.
- Added 2 parallel tests with data transform expression = "x"
  in combination with a filter. Before, these tests will fail but
  with the improved H5Z_xform_noop() function they work and result
  in the expected behavior.
- Small bug fix for one of parallel filter tests.

* Committing clang-format changes

* H5Ztrans: (feature) Added release note about detection of the
           simple data transform function "x".

- Added a brief explanation about the implemented improvement
  of the detection of the simple data transform function "x"
  to the RELEASE.txt file.

Co-authored-by: github-actions <41898282+github-actions[bot]@users.noreply.github.com>

release_docs/RELEASE.txt

@@ -935,6 +935,17 @@ Bug Fixes since HDF5-1.12.0 release
 ===================================
     Library
     -------
+    - Detection of simple data transform function "x"
+
+        In the case of the simple data transform function "x" the (parallel)
+        library recognizes this is the same as not applying this data transform
+        function. This improves the I/O performance. In the case of the parallel
+        library, it also avoids breaking to independent I/O, which makes it
+        possible to apply a filter when writing or reading data to or from
+        teh HDF5 file.
+
+        (JWSB - 2021/09/13)
+
     - Fixed an invalid read and memory leak when parsing corrupt file space
       info messages
 

src/H5Ztrans.c

@@ -1547,11 +1547,11 @@ H5Z_xform_create(const char *expr)
                     (HDisdigit(expr[i - 1]) || (expr[i - 1] == '.')) &&
                     (HDisdigit(expr[i + 1]) || (expr[i + 1] == '-') || (expr[i + 1] == '+')))
                     continue;
-            }
+            } /* end if */
 
             count++;
-        }
-    }
+        } /* end if */
+    }     /* end for */
 
     /* When there are no "x"'s in the equation (ie, simple transform case),
      * we don't need to allocate any space since no array will have to be
@@ -1749,11 +1749,19 @@ H5Z_xform_copy(H5Z_data_xform_t **data_xform_prop)
 hbool_t
 H5Z_xform_noop(const H5Z_data_xform_t *data_xform_prop)
 {
-    hbool_t ret_value = FALSE; /* Return value */
+    hbool_t ret_value = TRUE; /* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT_NOERR
 
-    ret_value = (data_xform_prop ? FALSE : TRUE);
+    if (data_xform_prop) {
+        ret_value = FALSE;
+
+        /* Check for trivial data tranformation: expression = "x" */
+        if ((HDstrlen(data_xform_prop->xform_exp) == 1) && data_xform_prop->dat_val_pointers &&
+            (data_xform_prop->dat_val_pointers->num_ptrs == 1)) {
+            ret_value = TRUE;
+        } /* end if */
+    }     /* end if */
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* H5Z_xform_noop() */

test/dtransform.c

@@ -582,6 +582,7 @@ test_specials(hid_t file)
     const char *special4 = "-x";
     const char *special5 = "+x";
     const char *special6 = "2e+1*x";
+    const char *special7 = "x";
 
     TESTING("data transform of some special cases")
 
@@ -726,6 +727,32 @@ test_specials(hid_t file)
 
     COMPARE_INT(read_buf, data_res)
 
+    if (H5Dclose(dset_id) < 0)
+        TEST_ERROR
+
+    /*-----------------------------
+     * Operation 7: x
+     * This operation will be
+     * treated if no function has
+     * been specified.
+     *----------------------------*/
+    if (H5Pset_data_transform(dxpl_id, special7) < 0)
+        TEST_ERROR;
+
+    for (row = 0; row < ROWS; row++)
+        for (col = 0; col < COLS; col++)
+            data_res[row][col] = transformData[row][col];
+
+    if ((dset_id = H5Dcreate2(file, "/special7", H5T_NATIVE_INT, dataspace, H5P_DEFAULT, H5P_DEFAULT,
+                              H5P_DEFAULT)) < 0)
+        TEST_ERROR
+    if (H5Dwrite(dset_id, H5T_NATIVE_INT, H5S_ALL, H5S_ALL, dxpl_id, transformData) < 0)
+        TEST_ERROR
+    if (H5Dread(dset_id, H5T_NATIVE_INT, H5S_ALL, H5S_ALL, H5P_DEFAULT, read_buf) < 0)
+        TEST_ERROR
+
+    COMPARE_INT(read_buf, data_res)
+
     if (H5Dclose(dset_id) < 0)
         TEST_ERROR