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, 59 insertions, 0 deletions

diff --git a/Source/Utils/Algorithms/LinearInterpolation.H b/Source/Utils/Algorithms/LinearInterpolation.H
new file mode 100644
index 000000000..32fdf7a6e
--- /dev/null
+++ b/Source/Utils/Algorithms/LinearInterpolation.H
@@ -0,0 +1,59 @@
+/* Copyright 2022 Luca Fedeli
+ *
+ * This file is part of WarpX.
+ *
+ * License: BSD-3-Clause-LBNL
+ */
+
+#ifndef WARPX_UTILS_ALGORITHMS_LINEAR_INTERPOLATION_H_
+#define WARPX_UTILS_ALGORITHMS_LINEAR_INTERPOLATION_H_
+
+#include <AMReX_Extension.H>
+#include <AMReX_GpuQualifiers.H>
+
+namespace utils::algorithms
+{
+    /** \brief Performs a linear interpolation
+     *
+     * Performs a linear interpolation at x given the 2 points
+     * (x0, f0) and (x1, f1)
+     */
+    template<typename T> AMREX_GPU_DEVICE AMREX_FORCE_INLINE
+    T linear_interp(T x0, T x1, T f0, T f1, T x)
+    {
+        return ((x1-x)*f0 + (x-x0)*f1)/(x1-x0);
+    }
+
+    /** \brief Performs a bilinear interpolation
+     *
+     * Performs a bilinear interpolation at (x,y) given the 4 points
+     * (x0, y0, f00), (x0, y1, f01), (x1, y0, f10), (x1, y1, f11).
+     */
+    template<typename T> AMREX_GPU_DEVICE AMREX_FORCE_INLINE
+    T bilinear_interp(T x0, T x1, T y0, T y1, T f00, T f01, T f10, T f11, T x, T y)
+    {
+        const T fx0 = linear_interp(x0, x1, f00, f10, x);
+        const T fx1 = linear_interp(x0, x1, f01, f11, x);
+        return linear_interp(y0, y1, fx0, fx1, y);
+    }
+
+    /** \brief Performs a trilinear interpolation
+     *
+     * Performs a trilinear interpolation at (x,y,z) given the 8 points
+     * (x0, y0, z0, f000), (x0, y0, z1, f001), (x0, y1, z0, f010), (x0, y1, z1, f011),
+     * (x1, y0, z0, f100), (x1, y0, z1, f101), (x1, y1, z0, f110), (x1, y1, z1, f111)
+     */
+    template<typename T> AMREX_GPU_DEVICE AMREX_FORCE_INLINE
+    T trilinear_interp(T x0, T x1,T y0, T y1, T z0, T z1,
+        T f000, T f001, T f010, T f011, T f100, T f101, T f110, T f111,
+        T x, T y, T z)
+    {
+        const T fxy0 = bilinear_interp(
+            x0, x1, y0, y1, f000, f010, f100, f110, x, y);
+        const T fxy1 = bilinear_interp(
+            x0, x1, y0, y1, f001, f011, f101, f111, x, y);
+        return linear_interp(z0, z1, fxy0, fxy1, z);
+    }
+}
+
+#endif //WARPX_UTILS_ALGORITHMS_LINEAR_INTERPOLATION_H_