add memswap.h, which provides in-place swapping.

src/Makefile.am

@@ -44,7 +44,7 @@ include_HEADERS = space.h runner.h queue.h task.h lock.h cell.h part.h const.h \
     common_io.h single_io.h multipole.h map.h tools.h partition.h clocks.h parser.h \
     physical_constants.h physical_constants_cgs.h potential.h version.h \
     hydro_properties.h riemann.h threadpool.h cooling.h cooling_struct.h sourceterms.h \
-    sourceterms_struct.h statistics.h
+    sourceterms_struct.h statistics.h memswap.h
 
 
 # Common source files
@@ -83,7 +83,8 @@ nobase_noinst_HEADERS = align.h approx_math.h atomic.h cycle.h error.h inline.h
 		 potential/softened_isothermal/potential.h \
 		 cooling/none/cooling.h cooling/none/cooling_struct.h \
 	         cooling/const_du/cooling.h cooling/const_du/cooling_struct.h \
-                 cooling/const_lambda/cooling.h cooling/const_lambda/cooling_struct.h 
+                 cooling/const_lambda/cooling.h cooling/const_lambda/cooling_struct.h \
+     memswap.h
 
 
 # Sources and flags for regular library

src/memswap.h

+/*******************************************************************************
+ * This file is part of SWIFT.
+ * Copyright (c) 2012 Pedro Gonnet (pedro.gonnet@durham.ac.uk)
+ *                    Matthieu Schaller (matthieu.schaller@durham.ac.uk)
+ *               2015 Peter W. Draper (p.w.draper@durham.ac.uk)
+ *               2016 John A. Regan (john.a.regan@durham.ac.uk)
+ *                    Tom Theuns (tom.theuns@durham.ac.uk)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ ******************************************************************************/
+#ifndef SWIFT_MEMSWAP_H
+#define SWIFT_MEMSWAP_H
+
+/* Config parameters. */
+#include "../config.h"
+
+#ifdef HAVE_IMMINTRIN_H
+/* Include the header file with the intrinsics for Intel architecture. */
+#include <immintrin.h>
+#endif
+
+#ifdef HAVE_ALTIVEC_H
+/* Include the header file with the intrinsics for Intel architecture. */
+#include <altivec.h>
+#endif
+
+/* Macro for in-place swap of two values a and b of type t. */
+#define swap_loop(t, a, b, c)  \
+  while (c >= sizeof(t)) {     \
+    register t temp = *(t *)a; \
+    *(t *)a = *(t *)b;         \
+    *(t *)b = temp;            \
+    a += sizeof(t);            \
+    b += sizeof(t);            \
+    bytes -= sizeof(t);        \
+  }
+
+/**
+ * @brief Swap the contents of two elements in-place.
+ *
+ * Keep in mind that this function works best when the underlying data
+ * is aligned to the vector length, e.g. with the @c __attribute__((aligned(32)))
+ * syntax, and the code is compiled with @c -funroll-loops.
+ *
+ * @param a Pointer to the first element.
+ * @param b Pointer to the second element.
+ * @param bytes Size, in bytes, of the data pointed to by @c a and @c b.
+ */
+__attribute__((always_inline)) inline void memswap(void *void_a, void *void_b,
+                                                   size_t bytes) {
+  char *a = (char *)void_a, *b = (char *)void_b;
+#ifdef __AVX512F__
+  swap_loop(__m512i, a, b, bytes)
+#endif
+#ifdef __AVX__
+  swap_loop(__m256i, a, b, bytes)
+#endif
+#ifdef __SSE2__
+  swap_loop(__m128i, a, b, bytes)
+#endif
+#ifdef __ALTIVEC__
+  swap_loop(vector int, a, b, bytes)
+#endif
+  swap_loop(size_t, a, b, bytes)
+  swap_loop(int, a, b, bytes)
+  swap_loop(short, a, b, bytes)
+  swap_loop(char, a, b, bytes)
+}
+
+#endif /* SWIFT_MEMSWAP_H */