Add experimental clamping filter

add a mini filter: h5z-clamp, with a filter ID of 45678

CMakeLists.txt

@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 3.14)
 
-project(H5Z-SPERR VERSION 0.2.0 LANGUAGES C CXX DESCRIPTION "HDF5 plugin for SPERR compression")
+project(H5Z-SPERR VERSION 0.2.1 LANGUAGES C CXX DESCRIPTION "HDF5 plugin for SPERR compression")
 
 set(CMAKE_C_STANDARD 11)
 set(CMAKE_CXX_STANDARD 14)
@@ -76,7 +76,7 @@ endif()
 # Start installation using GNU installation rules
 #
 include( GNUInstallDirs )
-install( TARGETS h5z-sperr LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR} )
+install( TARGETS h5z-sperr h5z-clamp LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR} )
 
 if( BUILD_CLI_UTILITIES )
   install( TARGETS generate_cd_values decode_cd_values

src/CMakeLists.txt

@@ -1,3 +1,6 @@
+#
+# The main H5Z-SPERR filter
+#
 add_library( h5z-sperr h5z-sperr.c
                        h5zsperr_helper.cpp
                        icecream.c
@@ -6,3 +9,10 @@ target_include_directories( h5z-sperr PUBLIC ${HDF5_INCLUDE_DIR}
                                       PUBLIC ${SPERR_INCLUDE_DIRS}
                                       PUBLIC ${CMAKE_SOURCE_DIR}/include )
 target_link_libraries( h5z-sperr PUBLIC ${HDF5_LIBRARIES} PUBLIC PkgConfig::SPERR )
+
+#
+# Experimental clamping filter
+#
+add_library( h5z-clamp h5z-clamp.c )
+target_include_directories( h5z-clamp PUBLIC ${HDF5_INCLUDE_DIR} )
+target_link_libraries( h5z-clamp PUBLIC ${HDF5_LIBRARIES} )

src/h5z-clamp.c

@@ -0,0 +1,127 @@
+/*
+ * This file contains the clamp filter class definition, H5Z_clamp_class_t,
+ * and necessary functions required by the HDF5 plugin architecture:
+ * - can_apply()
+ * - set_local()
+ * - filter()
+ * - get_plugin_info()
+ * - get_plugin_type()
+ */
+
+#define H5Z_FILTER_CLAMP 45678
+
+#include <assert.h>
+#include <stdlib.h>
+
+#include <H5PLextern.h>
+#include <hdf5.h>
+
+static htri_t H5Z_can_apply_clamp(hid_t dcpl_id, hid_t type_id, hid_t space_id)
+{
+  /*
+   * 	dcpl_id	  Dataset creation property list identifier
+   * 	type_id	  Datatype identifier
+   * 	space_id  Dataspace identifier
+   */
+
+  /* Get datatype class. Fail if not floats. */
+  if (H5Tget_class(type_id) != H5T_FLOAT) {
+    H5Epush(H5E_DEFAULT, __FILE__, __func__, __LINE__, H5E_ERR_CLS, H5E_PLINE, H5E_BADTYPE,
+            "bad data type. Only floats are supported in H5Z-CLAMP");
+    return 0;
+  }
+  size_t type_size = H5Tget_size(type_id);
+  assert(type_size == 4 || type_size == 8);
+
+  return 1;
+}
+
+static herr_t H5Z_set_local_clamp(hid_t dcpl_id, hid_t type_id, hid_t space_id)
+{
+  /*
+   * 	dcpl_id	  Dataset creation property list identifier
+   * 	type_id	  Datatype identifier
+   * 	space_id  Dataspace identifier
+   */
+
+  /* Get the datatype size. It must be 4 or 8, since the float type is verified by `can_apply`. */
+  unsigned int is_float = H5Tget_size(type_id) == 4 ? 1 : 0;
+
+  /*
+   * Assemble the meta info to be stored.
+   * [0] : float/double
+   */
+  size_t cd_nelems = 1;
+  unsigned int cd_values[1] = {is_float};
+  H5Pmodify_filter(dcpl_id, H5Z_FILTER_CLAMP, H5Z_FLAG_MANDATORY, cd_nelems, cd_values);
+
+  return 1;
+}
+
+static size_t H5Z_filter_clamp(unsigned int flags,
+                               size_t cd_nelmts,
+                               const unsigned int cd_values[],
+                               size_t nbytes,
+                               size_t* buf_size,
+                               void** buf)
+{
+  int is_float = cd_values[0];
+  assert(is_float == 1 || is_float == 0);
+
+  if (flags & H5Z_FLAG_REVERSE) { /* Decompression */
+
+    if (is_float) {
+      if (nbytes % 4) {
+        H5Epush(H5E_DEFAULT, __FILE__, __func__, __LINE__, H5E_ERR_CLS, H5E_PLINE, H5E_BADSIZE,
+                "Decompression: input buffer len isn't right.");
+        return 0;
+      }
+      const size_t nelem = nbytes / 4;
+      float* p = (float*)(*buf);
+      for (size_t i = 0; i < nelem; i++) {
+        if (p[i] < 0.f)
+          p[i] = 0.f;
+      }
+    }
+    else {
+      if (nbytes % 8) {
+        H5Epush(H5E_DEFAULT, __FILE__, __func__, __LINE__, H5E_ERR_CLS, H5E_PLINE, H5E_BADSIZE,
+                "Decompression: input buffer len isn't right.");
+        return 0;
+      }
+      const size_t nelem = nbytes / 8;
+      double* p = (double*)(*buf);
+      for (size_t i = 0; i < nelem; i++) {
+        if (p[i] < 0.0)
+          p[i] = 0.0;
+      }
+    }
+
+    return *buf_size;
+
+  }      /* Finish Decompression */
+  else { /* Compression */
+
+    /* Nothing to be done during compression :) */
+    return *buf_size;
+  }
+}
+
+const H5Z_class2_t H5Z_clamp_class_t = {H5Z_CLASS_T_VERS, /* H5Z_class_t version */
+                                        H5Z_FILTER_CLAMP, /* Filter id number    */
+                                        1,                /* encoder_present flag (set to true) */
+                                        1,                /* decoder_present flag (set to true) */
+                                        "H5Z-CLAMP",      /* Filter name for debugging  */
+                                        H5Z_can_apply_clamp, /* The "can apply" callback   */
+                                        H5Z_set_local_clamp, /* The "set local" callback   */
+                                        H5Z_filter_clamp};   /* The actual filter function */
+
+const void* H5PLget_plugin_info()
+{
+  return &H5Z_clamp_class_t;
+}
+
+H5PL_type_t H5PLget_plugin_type()
+{
+  return H5PL_TYPE_FILTER;
+}

src/h5z-sperr.c

@@ -248,7 +248,7 @@ static herr_t H5Z_set_local_sperr(hid_t dcpl_id, hid_t type_id, hid_t space_id)
 
   H5Pmodify_filter(dcpl_id, H5Z_FILTER_SPERR, H5Z_FLAG_MANDATORY, cd_nelems, cd_values);
 
-  return 0;
+  return 1;
 }
 
 static size_t H5Z_filter_sperr(unsigned int flags,