From 0931f1b5886f6bcc02f8f7a656399996eef74393 Mon Sep 17 00:00:00 2001
From: Silvano Seva <silseva@fastwebnet.it>
Date: Fri, 4 Dec 2020 18:13:24 +0100
Subject: [PATCH] Utility for interpolation of calibration parameters

---
 openrtx/include/calibration/calibUtils.h | 45 +++++++++++++++++++++
 openrtx/src/calibUtils.c                 | 51 ++++++++++++++++++++++++
 2 files changed, 96 insertions(+)
 create mode 100644 openrtx/include/calibration/calibUtils.h
 create mode 100644 openrtx/src/calibUtils.c

diff --git a/openrtx/include/calibration/calibUtils.h b/openrtx/include/calibration/calibUtils.h
new file mode 100644
index 00000000..1e746ef1
--- /dev/null
+++ b/openrtx/include/calibration/calibUtils.h
@@ -0,0 +1,45 @@
+/***************************************************************************
+ *   Copyright (C) 2020 by Federico Amedeo Izzo IU2NUO,                    *
+ *                         Niccolò Izzo IU2KIN,                            *
+ *                         Silvano Seva IU2KWO                             *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU 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 General Public License     *
+ *   along with this program; if not, see <http://www.gnu.org/licenses/>   *
+ ***************************************************************************/
+
+#ifndef CALIB_UTILS_H
+#define CALIB_UTILS_H
+
+#include <datatypes.h>
+#include <stdint.h>
+
+/**
+ * This function allows to obtain the value of a given calibration parameter for
+ * frequencies outside the calibration points. It works by searching the two
+ * calibration points containing the target frequency and then by linearly
+ * interpolating the calibration parameter among these two points.
+ * @param freq: target frequency for which a calibration value has to be
+ * computed.
+ * @param calPoints: pointer to the vector containing the frequencies of the
+ * calibration points.
+ * @param param: pointer to the vector containing the values for the calibration
+ * parameter, it must have the same length of the one containing the frequencies
+ * of calibration points.
+ * @param elems: number of elements of both the vectors for calibration parameter
+ * and frequencies.
+ * @return value for the calibration parameter at the given frequency point.
+ */
+uint8_t interpCalParameter(freq_t freq, freq_t *calPoints, uint8_t *param,
+                                                           uint8_t elems);
+
+#endif /* CALIB_UTILS_H */
diff --git a/openrtx/src/calibUtils.c b/openrtx/src/calibUtils.c
new file mode 100644
index 00000000..f9ce2083
--- /dev/null
+++ b/openrtx/src/calibUtils.c
@@ -0,0 +1,51 @@
+/***************************************************************************
+ *   Copyright (C) 2020 by Federico Amedeo Izzo IU2NUO,                    *
+ *                         Niccolò Izzo IU2KIN,                            *
+ *                         Silvano Seva IU2KWO                             *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU 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 General Public License     *
+ *   along with this program; if not, see <http://www.gnu.org/licenses/>   *
+ ***************************************************************************/
+
+#include <calibUtils.h>
+
+uint8_t interpCalParameter(freq_t freq, freq_t *calPoints, uint8_t *param,
+                                                           uint8_t elems)
+{
+
+    if(freq <= calPoints[0])         return param[0];
+    if(freq >= calPoints[elems - 1]) return param[elems - 1];
+
+    /* Find calibration point nearest to target frequency */
+    uint8_t pos = 0;
+    for(; pos < elems; pos++)
+    {
+        if(calPoints[pos] >= freq) break;
+    }
+
+    uint8_t interpValue = 0;
+    freq_t  delta = calPoints[pos] - calPoints[pos - 1];
+
+    if(param[pos - 1] < param[pos])
+    {
+        interpValue = param[pos - 1] + ((freq - calPoints[pos - 1]) *
+                                        (param[pos] - param[pos - 1]))/delta;
+    }
+    else
+    {
+        interpValue = param[pos - 1] - ((freq - calPoints[pos - 1]) *
+                                       (param[pos - 1] - param[pos]))/delta;
+    }
+
+    return interpValue;
+}