add: support for checking sign of integer datatype. (#78)

An integer HDF5 datatype (i.e. one that has class `H5T_INTEGER`) can be
signed or unsigned. This commit adds a class `IntegerType` which
supports the method `isSigned`.

Intended use:

    auto dtype = /* obtain datatype */;
    if(dtype.getClass() == DataTypeClass::Integer) {
      auto int_type = dtype.asIntegerType();
      if(int_type.isSigned()) {
        // ...
      }

Author: 1uc

include/highfive/H5DataType.hpp

@@ -54,6 +54,7 @@ inline DataTypeClass operator&(DataTypeClass lhs, DataTypeClass rhs) {
 }
 
 class StringType;
+class IntegerType;
 
 ///
 /// \brief HDF5 Data Type
@@ -97,6 +98,11 @@ class DataType: public Object {
     ///
     StringType asStringType() const;
 
+    ///
+    /// \brief Returns this datatype as a `IntegerType`.
+    ///
+    IntegerType asIntegerType() const;
+
     ///
     /// \brief Check the DataType was default constructed.
     ///
@@ -179,6 +185,22 @@ class VariableLengthStringType: public StringType {
     explicit VariableLengthStringType(CharacterSet character_set = CharacterSet::Ascii);
 };
 
+///
+/// \brief An Integer datatype (i.e. H5T_INTEGER).
+///
+/// Provides access to the API that's only valid for integers. Use
+/// DataType::asIntegerType to convert from a generic DataType.
+///
+class IntegerType: public DataType {
+  public:
+    bool isSigned() {
+        return detail::h5t_get_sign(getId()) != H5T_SGN_NONE;
+    }
+
+  protected:
+    using DataType::DataType;
+    friend class DataType;
+};
 
 ///
 /// \brief create an HDF5 DataType from a C++ type

include/highfive/bits/H5DataType_misc.hpp

@@ -73,6 +73,18 @@ inline StringType DataType::asStringType() const {
     return StringType(_hid);
 }
 
+inline IntegerType DataType::asIntegerType() const {
+    if (getClass() != DataTypeClass::Integer) {
+        throw DataTypeException("Invalid conversion to IntegerType.");
+    }
+
+    if (isValid()) {
+        detail::h5i_inc_ref(_hid);
+    }
+
+    return IntegerType(_hid);
+}
+
 inline std::string DataType::string() const {
     return type_class_string(getClass()) + std::to_string(getSize() * 8);
 }

include/highfive/bits/h5t_wrapper.hpp

@@ -24,6 +24,14 @@ inline hsize_t h5t_get_size(hid_t hid) {
     return size;
 }
 
+inline H5T_sign_t h5t_get_sign(hid_t type_id) {
+    auto sign = H5Tget_sign(type_id);
+    if (sign == H5T_SGN_ERROR) {
+        HDF5ErrMapper::ToException<DataTypeException>("Error getting the sign of datatype.");
+    }
+    return sign;
+}
+
 inline H5T_cset_t h5t_get_cset(hid_t hid) {
     auto cset = H5Tget_cset(hid);
     if (cset == H5T_CSET_ERROR) {

tests/unit/tests_high_five_base.cpp

@@ -2332,6 +2332,21 @@ TEST_CASE("HighFiveDataTypeClass") {
     CHECK(((Float | String) & String) == String);
 }
 
+TEST_CASE("HighFiveIntegerType") {
+    SECTION("signed int") {
+        auto dtype = create_datatype<int>().asIntegerType();
+        CHECK(dtype.isSigned());
+    }
+    SECTION("unsigned int") {
+        auto dtype = create_datatype<unsigned int>().asIntegerType();
+        CHECK(!dtype.isSigned());
+    }
+    SECTION("invalid conversion") {
+        auto dtype = create_datatype<double>();
+        CHECK_THROWS(dtype.asIntegerType());
+    }
+}
+
 #ifdef HIGHFIVE_TEST_EIGEN
 
 template <typename T>