Moved FIR filter class to a dedicated header file

openrtx/include/core/dsp.h

@@ -21,8 +21,13 @@
 #ifndef DSP_H
 #define DSP_H
 
-#include <inttypes.h>
+#include <stdbool.h>
-#include <stdlib.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 typedef int16_t audio_sample_t;
 
@@ -31,14 +36,6 @@ typedef int16_t audio_sample_t;
  * input or output signals when implementing digital modes on OpenRTX.
  */
 
-#ifdef __cplusplus
-
-#include <array>
-#include <cstddef>
-
-extern "C" {
-#endif
-
 /**
  * Data structure holding the internal state of a filter.
  */
@@ -90,72 +87,6 @@ void dsp_invertPhase(audio_sample_t *buffer, uint16_t length);
 
 #ifdef __cplusplus
 }
-
-/**
- * Class for FIR filter with configurable coefficients.
- * Adapted from the original implementation by Rob Riggs, Mobilinkd LLC.
- */
-template < size_t N >
-class Fir
-{
-public:
-
-    /**
-     * Constructor.
-     *
-     * @param taps: reference to a std::array of floating poing values representing
-     * the FIR filter coefficients.
-     */
-    Fir(const std::array< float, N >& taps) : taps(taps), pos(0)
-    {
-        reset();
-    }
-
-    /**
-     * Destructor.
-     */
-    ~Fir() { }
-
-    /**
-     * Perform one step of the FIR filter, computing a new output value given
-     * the input value and the history of previous input values.
-     *
-     * @param input: FIR input value for the current time step.
-     * @return FIR output as a function of the current and past input values.
-     */
-    float operator()(const float& input)
-    {
-        hist[pos++] = input;
-        if(pos >= N) pos = 0;
-
-        float  result = 0.0;
-        size_t index  = pos;
-
-        for(size_t i = 0; i < N; i++)
-        {
-            index   = (index != 0 ? index - 1 : N - 1);
-            result += hist[index] * taps[i];
-        }
-
-        return result;
-    }
-
-    /**
-     * Reset FIR history, clearing the memory of past values.
-     */
-    void reset()
-    {
-        hist.fill(0);
-        pos = 0;
-    }
-
-private:
-
-    const std::array< float, N >& taps;    ///< FIR filter coefficients.
-    std::array< float, N >        hist;    ///< History of past inputs.
-    size_t                        pos;     ///< Current position in history.
-};
-
 #endif // __cplusplus
 
 #endif /* DSP_H */

openrtx/include/core/fir.hpp

@@ -0,0 +1,97 @@
+/***************************************************************************
+ *   Copyright (C) 2022 by Federico Amedeo Izzo IU2NUO,                    *
+ *                         Niccolò Izzo IU2KIN,                            *
+ *                         Silvano Seva IU2KWO,                            *
+ *                         Frederik Saraci IU2NRO                          *
+ *                                                                         *
+ *   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 FIR_H
+#define FIR_H
+
+#ifndef __cplusplus
+#error This header is C++ only!
+#endif
+
+#include <array>
+#include <cstddef>
+#include <cstdint>
+
+/**
+ * Class for FIR filter with configurable coefficients.
+ * Adapted from the original implementation by Rob Riggs, Mobilinkd LLC.
+ */
+template < size_t N >
+class Fir
+{
+public:
+
+    /**
+     * Constructor.
+     *
+     * @param taps: reference to a std::array of floating poing values representing
+     * the FIR filter coefficients.
+     */
+    Fir(const std::array< float, N >& taps) : taps(taps), pos(0)
+    {
+        reset();
+    }
+
+    /**
+     * Destructor.
+     */
+    ~Fir() { }
+
+    /**
+     * Perform one step of the FIR filter, computing a new output value given
+     * the input value and the history of previous input values.
+     *
+     * @param input: FIR input value for the current time step.
+     * @return FIR output as a function of the current and past input values.
+     */
+    float operator()(const float& input)
+    {
+        hist[pos] = input;
+        pos = (pos + 1) % N;
+
+        float  result = 0.0;
+        size_t index  = pos;
+
+        for(size_t i = 0; i < N; i++)
+        {
+            index   = (index != 0 ? index - 1 : N - 1);
+            result += hist[index] * taps[i];
+        }
+
+        return result;
+    }
+
+    /**
+     * Reset FIR history, clearing the memory of past values.
+     */
+    void reset()
+    {
+        hist.fill(0);
+        pos = 0;
+    }
+
+private:
+
+    const std::array< float, N >& taps;    ///< FIR filter coefficients.
+    std::array< float, N >        hist;    ///< History of past inputs.
+    size_t                        pos;     ///< Current position in history.
+};
+
+#endif /* DSP_H */

openrtx/include/protocols/M17/M17DSP.h

@@ -27,7 +27,7 @@
 #error This header is C++ only!
 #endif
 
-#include <dsp.h>
+#include <fir.hpp>
 #include <array>
 
 namespace M17

openrtx/src/core/dsp.cpp

@@ -111,20 +111,3 @@ void dsp_invertPhase(audio_sample_t *buffer, uint16_t length)
         buffer[i] = -buffer[i];
     }
 }
-
-template<size_t order>
-void dsp_applyFIR(audio_sample_t *buffer,
-                  uint16_t length,
-                  std::array<float, order> taps)
-{
-    for(int i = length - 1; i >= 0; i--)
-    {
-        float acc = 0.0f;
-        for(uint16_t j = 0; j < order; j++)
-        {
-            if (i >= j)
-                acc += buffer[i - j] * taps[j];
-        }
-        buffer[i] = (audio_sample_t) acc;
-    }
-}