From 502cbee5b21841b09a04996a70c3ec1f89f11ce7 Mon Sep 17 00:00:00 2001
From: Matthieu Schaller <schaller@strw.leidenuniv.nl>
Date: Tue, 21 Apr 2020 23:55:40 +0200
Subject: [PATCH] Added a function to compute the binomial coefficient of a
pair of integers
---
src/Makefile.am | 2 +-
src/binomial.h | 46 ++++++++++++++++++++++++++++++++++++++++++++++
src/multipole.h | 1 +
3 files changed, 48 insertions(+), 1 deletion(-)
create mode 100644 src/binomial.h
diff --git a/src/Makefile.am b/src/Makefile.am
index 56b8f48e74..7c886448aa 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -52,7 +52,7 @@ include_HEADERS = space.h runner.h queue.h task.h lock.h cell.h part.h const.h \
chemistry.h chemistry_io.h chemistry_struct.h cosmology.h restart.h space_getsid.h utilities.h \
mesh_gravity.h cbrt.h exp10.h velociraptor_interface.h swift_velociraptor_part.h outputlist.h \
logger_io.h tracers_io.h tracers.h tracers_struct.h star_formation_io.h fof.h fof_struct.h fof_io.h \
- multipole.h multipole_struct.h \
+ multipole.h multipole_struct.h binomial.h \
star_formation_struct.h star_formation.h star_formation_iact.h \
star_formation_logger.h star_formation_logger_struct.h \
pressure_floor.h pressure_floor_struct.h pressure_floor_iact.h \
diff --git a/src/binomial.h b/src/binomial.h
new file mode 100644
index 0000000000..24ea90e656
--- /dev/null
+++ b/src/binomial.h
@@ -0,0 +1,46 @@
+/*******************************************************************************
+ * This file is part of SWIFT.
+ * Copyright (c) 2020 Matthieu Schaller (schaller@strw.leidenuniv.nl)
+ *
+ * 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_BINOMIAL_H
+#define SWIFT_BINOMIAL_H
+
+#include "error.h"
+#include "inline.h"
+
+/**
+ * @brief Compute the binomial coefficient (n, k)
+ *
+ * Only valid for values up to n = 5.
+ */
+__attribute__((const)) INLINE static int binomial(const int n, const int k) {
+
+#ifdef SWIFT_DEBUG_CHECKS
+ assert(n >= 0);
+ assert(k >= 0);
+ assert(n <= 5);
+ assert(k <= n);
+#endif
+
+ static const int coeffs[6][6] = {{1, 0, 0, 0, 0, 0}, {1, 1, 0, 0, 0, 0},
+ {1, 2, 1, 0, 0, 0}, {1, 3, 3, 1, 0, 0},
+ {1, 4, 6, 4, 1, 0}, {1, 5, 10, 10, 5, 1}};
+
+ return coeffs[n][k];
+}
+
+#endif /* SWIFT_BINOMIAL_H */
diff --git a/src/multipole.h b/src/multipole.h
index 79dde23d2d..52e49417e2 100644
--- a/src/multipole.h
+++ b/src/multipole.h
@@ -30,6 +30,7 @@
/* Includes. */
#include "accumulate.h"
#include "align.h"
+#include "binomial.h"
#include "const.h"
#include "error.h"
#include "gravity.h"
--
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