Partial refactoring of the utils directory (#3404)

* initial work to clean WarpX Utils

* remove AMRCore from Ionization tables

* progress

* refactoring of a part of the utils directory

* fix bug

* fixed bug

* fixed bug

* remove debug line accidentally slipped into the code

* remove debug line accidentally slipped into the code

* remove debug line accidentally slipped into the code

* cleaning

* fixed bug

1 files changed, 49 insertions, 0 deletions

diff --git a/Source/Utils/Algorithms/UpperBound.H b/Source/Utils/Algorithms/UpperBound.H
new file mode 100644
index 000000000..8a528971a
--- /dev/null
+++ b/Source/Utils/Algorithms/UpperBound.H
@@ -0,0 +1,49 @@
+/* Copyright 2022 Luca Fedeli
+ *
+ * This file is part of WarpX.
+ *
+ * License: BSD-3-Clause-LBNL
+ */
+
+#ifndef WARPX_UTILS_ALGORITHMS_UPPER_BOUND_H_
+#define WARPX_UTILS_ALGORITHMS_UPPER_BOUND_H_
+
+#include <AMReX_Extension.H>
+#include <AMReX_GpuQualifiers.H>
+
+namespace utils::algorithms
+{
+
+    /** \brief Returns a pointer to the first element in the range [first, last) that is greater than val
+     *
+     * A re-implementation of the upper_bound algorithm suitable for GPU kernels.
+     *
+     * @param first: pointer to left limit of the range to consider
+     * @param last: pointer to right limit of the range to consider
+     * @param val: value to compare the elements of [first, last) to
+     */
+    template<typename T> AMREX_GPU_DEVICE AMREX_FORCE_INLINE
+    const T* upper_bound(const T* first, const T* last, const T& val)
+    {
+        const T* it;
+        size_t count, step;
+        count = last-first;
+        while(count>0){
+            it = first;
+            step = count/2;
+            it += step;
+            if (!(val<*it)){
+                first = ++it;
+                count -= step + 1;
+            }
+            else{
+                count = step;
+            }
+        }
+
+        return first;
+    }
+
+}
+
+#endif //WARPX_UTILS_ALGORITHMS_UPPER_BOUND_H_