GPU: add constexpr version of qStr2Tag

Signed-off-by: Felix Schlepper <felix.schlepper@cern.ch>

Author: f3sch

GPU/GPUTracking/utils/strtag.h

@@ -15,13 +15,29 @@
 #ifndef STRTAG_H
 #define STRTAG_H
 
+#include <string_view>
+#include <cstring>
 #include <stdexcept>
+#include <cstdint>
 #include <string>
+#include <type_traits>
+
+template <class T = uint64_t, std::size_t N>
+constexpr T qStr2Tag(const char (&str)[N])
+{
+  static_assert(std::is_trivially_copyable_v<T>);
+  static_assert(N - 1 == sizeof(T), "Invalid tag length");
+  T value{};
+  for (std::size_t i = 0; i < sizeof(T); ++i) {
+    value |= T(static_cast<unsigned char>(str[i])) << (i * 8);
+  }
+  return value;
+}
 
 template <class T = uint64_t>
-constexpr T qStr2Tag(const char* str)
+constexpr T qStr2Tag(std::string_view str)
 {
-  if (strlen(str) != sizeof(T)) {
+  if (str.size() != sizeof(T)) {
     throw std::runtime_error("Invalid tag length");
   }
   T tmp;