use djb2 instead of std::hash for multiplatform stability

Author: Michal Tichák

Framework/src/HashDataDescription.cxx

@@ -9,7 +9,7 @@
 // granted to it by virtue of its status as an Intergovernmental Organization
 // or submit itself to any jurisdiction.
 
-#include <iostream>
+#include <iomanip>
 #include <sstream>
 
 #include "QualityControl/HashDataDescription.h"
@@ -20,29 +20,36 @@ namespace o2::quality_control::core
 namespace hash
 {
 
+// djb2 is used instead of std::hash<std::string> to be consisted over different architectures
+auto djb2(const std::string& input) -> size_t
+{
+  size_t hash = 5381;
+  for (const auto c : input) {
+    hash = ((hash << 5) + hash) + c; /* hash * 33 + c */
+  }
+  return hash;
+}
+
 // creates hash of input string and returns hexadecimal representation
-auto to_hexa(const std::string& input, size_t hash_length) -> std::string
+// if created hash has smaller amount of digits than requested, required number of zeros is appended
+auto to_hex(const std::string& input, size_t hashLength) -> std::string
 {
   std::stringstream ss;
-  ss << std::hex << std::hash<std::string>{}(input);
-  return std::move(ss).str().substr(0, hash_length);
+  ss << std::setfill('0') << std::left << std::setw(hashLength) << std::noshowbase << std::hex << djb2(input);
+  return std::move(ss).str().substr(0, hashLength);
 };
 
 } // namespace hash
 
-o2::header::DataDescription createDataDescription(const std::string& name, size_t hashLength)
+auto createDataDescription(const std::string& name, size_t hashLength) -> o2::header::DataDescription
 {
   o2::header::DataDescription description{};
+
   if (name.size() <= o2::header::DataDescription::size) {
     description.runtimeInit(name.c_str());
     return description;
   } else {
-
-    std::stringstream ss{};
-    ss << std::hex << std::hash<std::string>{}(name);
-
-    description.runtimeInit(name.substr(0, o2::header::DataDescription::size - hashLength).append(hash::to_hexa(name, hashLength)).c_str());
-    std::cout << description.str << "\n";
+    description.runtimeInit(name.substr(0, o2::header::DataDescription::size - hashLength).append(hash::to_hex(name, hashLength)).c_str());
     return description;
   }
 }

Framework/test/testAggregatorRunner.cxx

@@ -53,7 +53,7 @@ std::pair<AggregatorRunnerConfig, std::vector<AggregatorConfig>> getAggregatorCo
 TEST_CASE("test_aggregator_runner_static")
 {
   CHECK((AggregatorRunner::createAggregatorRunnerDataDescription("qwertyuiop") == DataDescription("qwertyuiop")));
-  CHECK((AggregatorRunner::createAggregatorRunnerDataDescription("012345678901234567890") == DataDescription("012345678901a4a0")));
+  CHECK((AggregatorRunner::createAggregatorRunnerDataDescription("012345678901234567890") == DataDescription("012345678901639b")));
   CHECK_THROWS_AS(AggregatorRunner::createAggregatorRunnerDataDescription(""), AliceO2::Common::FatalException);
 }
 

Framework/test/testCheck.cxx

@@ -78,7 +78,7 @@ BOOST_AUTO_TEST_CASE(test_check_long_description)
   BOOST_REQUIRE_EQUAL(check.getInputs().size(), 1);
   BOOST_CHECK_EQUAL(check.getInputs()[0], (InputSpec{ { "mo" }, "QTST", "skeletonTask", 0, Lifetime::Sporadic }));
 
-  BOOST_CHECK_EQUAL(check.getOutputSpec(), (OutputSpec{ "CDET", "singleCheckLa881", 0, Lifetime::Sporadic }));
+  BOOST_CHECK_EQUAL(check.getOutputSpec(), (OutputSpec{ "CDET", "singleCheckL9fdb", 0, Lifetime::Sporadic }));
 }
 
 std::shared_ptr<MonitorObject> dummyMO(const std::string& objName)

Framework/test/testTaskRunner.cxx

@@ -81,7 +81,7 @@ BOOST_AUTO_TEST_CASE(test_task_runner_static)
 {
   BOOST_CHECK_EQUAL(TaskRunner::createTaskDataOrigin("DET"), DataOrigin("QDET"));
   BOOST_CHECK(TaskRunner::createTaskDataDescription("qwertyuiop") == DataDescription("qwertyuiop"));
-  BOOST_CHECK(TaskRunner::createTaskDataDescription("012345678901234567890") == DataDescription("012345678901a4a0"));
+  BOOST_CHECK(TaskRunner::createTaskDataDescription("012345678901234567890") == DataDescription("012345678901639b"));
   BOOST_CHECK_THROW(TaskRunner::createTaskDataDescription(""), AliceO2::Common::FatalException);
   BOOST_CHECK_EQUAL(TaskRunner::createTaskRunnerIdString(), "qc-task");
 }