Improved and generalized ieee754 is different function

Author: andreagilardoni

Diff for: src/property/math_utils.h

@@ -0,0 +1,29 @@
+/*
+  This file is part of the ArduinoIoTCloud library.
+
+  Copyright (c) 2024 Arduino SA
+
+  This Source Code Form is subject to the terms of the Mozilla Public
+  License, v. 2.0. If a copy of the MPL was not distributed with this
+  file, You can obtain one at http://mozilla.org/MPL/2.0/.
+*/
+#pragma once
+#include <math.h>
+
+namespace arduino { namespace math {
+
+    template<typename T>
+    inline bool ieee754_different(const T a, const T b, const T delta = 0.0) {
+        /* The following comparison is introduced to take into account the very peculiar
+        * way of handling NaN values by the standard IEEE754.
+        * We consider two floating point number different if their binary representation is different.
+        * or if those two IEEE754 values are numbers or zero(which is handled on its own) exceed
+        * a certain threshold
+        */
+        return memcmp((uint8_t*)&a, (uint8_t*)&b, sizeof(b)) != 0 && (
+            (fpclassify(a) != FP_NORMAL && fpclassify(a) != FP_ZERO) ||
+            (fpclassify(b) != FP_NORMAL && fpclassify(b) != FP_ZERO) ||
+            fabs(a - b) >= delta
+        );
+    }
+}}

Diff for: src/property/types/CloudFloat.h

@@ -19,6 +19,7 @@
 #define CLOUDFLOAT_H_
 
 #include <math.h>
+#include "../math_utils.h"
 
 /******************************************************************************
    INCLUDE
@@ -46,10 +47,7 @@ class CloudFloat : public Property {
       return _value;
     }
     virtual bool isDifferentFromCloud() {
-      if (std::isnan(_value) || std::isnan(_cloud_value)) {
-        return std::isnan(_value) != std::isnan(_cloud_value);
-      }
-      return _value != _cloud_value && fabs(_value - _cloud_value) >= Property::_min_delta_property;
+      return arduino::math::ieee754_different(_value, _cloud_value, Property::_min_delta_property);
     }
     virtual void fromCloudToLocal() {
       _value = _cloud_value;

Diff for: src/property/types/CloudWrapperFloat.h

@@ -19,6 +19,7 @@
 #define CLOUDWRAPPERFLOAT_H_
 
 #include <math.h>
+#include "../math_utils.h"
 
 /******************************************************************************
    INCLUDE
@@ -39,10 +40,7 @@ class CloudWrapperFloat : public CloudWrapperBase {
   public:
     CloudWrapperFloat(float& v) : _primitive_value(v), _cloud_value(v), _local_value(v) {}
     virtual bool isDifferentFromCloud() {
-      if (std::isnan(_primitive_value) || std::isnan(_cloud_value)) {
-        return std::isnan(_primitive_value) != std::isnan(_cloud_value);
-      }
-      return _primitive_value != _cloud_value && fabs(_primitive_value - _cloud_value) >= Property::_min_delta_property;
+      return arduino::math::ieee754_different(_primitive_value, _cloud_value, Property::_min_delta_property);
     }
     virtual void fromCloudToLocal() {
       _primitive_value = _cloud_value;