From 8056716c838b7968e8093f7949ac0fc4e9898da5 Mon Sep 17 00:00:00 2001
From: Jacob Kegerreis <jacob.kegerreis@durham.ac.uk>
Date: Wed, 16 May 2018 22:19:29 +0100
Subject: [PATCH] Add generic utility function to find a value's position in an
array
---
src/utilities.h | 92 +++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 92 insertions(+)
create mode 100644 src/utilities.h
diff --git a/src/utilities.h b/src/utilities.h
new file mode 100644
index 0000000000..35cf0ea4b3
--- /dev/null
+++ b/src/utilities.h
@@ -0,0 +1,92 @@
+/*******************************************************************************
+ * This file is part of SWIFT.
+ * Copyright (c) 2018 Jacob Kegerreis (jacob.kegerreis@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_UTILITIES_H
+#define SWIFT_UTILITIES_H
+
+/**
+ * @brief Search for a value in a monotonic array to find the index such that
+ * array[index] < value < array[index + 1]
+ *
+ * @param x The value to find
+ * @param arr The array to search
+ * @param n The length of the array
+ * @param i The found index
+ *
+ * Set -1 and n for x below and above the array edge values respectively.
+ */
+void find_value_in_monotonic_array(float x, float *arr, int n, int *i) {
+
+ int is_incr = (arr[n-1] > arr[0]); // Increasing or decreasing?
+ int i_mid, i_low = 0, i_high = n;
+
+ // Until arr[i_low] < x < arr[i_high=i_low+1]
+ while (i_high - i_low > 1) {
+ i_mid = (i_high + i_low) >> 1; // Middle index
+
+ // If mid < x and increasing or x < mid and decreasing
+ if ((arr[i_mid] <= x) == is_incr)
+ i_low = i_mid;
+ else
+ i_high = i_mid;
+ }
+
+ // Set i with the found i_low, or an error value if outside the array
+ if (x < arr[0])
+ *i = -1;
+ else if (arr[n-1] <= x)
+ *i = n;
+ else
+ *i = i_low;
+}
+
+#endif /* SWIFT_UTILITIES_H */
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--
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