From 481df9ee3d4bc05cb35299da92dbfeb7939c5c5c Mon Sep 17 00:00:00 2001
From: Bertrand Songis <bsongis@gmail.com>
Date: Sat, 4 Mar 2017 10:14:38 +0100
Subject: [PATCH] [Horus] Fixes #3775 (#4544)

* [Horus] Fixes #3775

Quick fix ... comments welcome :)

* Better hash function for strings

* One comment, one!

* One comment, one!
---
 radio/src/gui/480x272/widgets/modelbmp.cpp | 16 ++++++++--------
 radio/src/maths.cpp                        | 14 +++++++++++++-
 radio/src/opentx.h                         |  2 +-
 3 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/radio/src/gui/480x272/widgets/modelbmp.cpp b/radio/src/gui/480x272/widgets/modelbmp.cpp
index 3d6222683..131d59b2b 100644
--- a/radio/src/gui/480x272/widgets/modelbmp.cpp
+++ b/radio/src/gui/480x272/widgets/modelbmp.cpp
@@ -25,9 +25,9 @@ class ModelBitmapWidget: public Widget
   public:
     ModelBitmapWidget(const WidgetFactory * factory, const Zone & zone, Widget::PersistentData * persistentData):
       Widget(factory, zone, persistentData),
-      buffer(NULL)
+      buffer(NULL),
+      deps_hash(0)
     {
-      memset(bitmapFilename, 255, sizeof(bitmapFilename));
     }
 
     virtual ~ModelBitmapWidget()
@@ -65,11 +65,12 @@ class ModelBitmapWidget: public Widget
 
     virtual void refresh()
     {
-      if (memcmp(bitmapFilename, g_model.header.bitmap, sizeof(g_model.header.bitmap)) != 0 ||
-          memcmp(modelName, g_model.header.name, sizeof(g_model.header.name)) != 0) {
+      uint32_t new_hash = hash(g_model.header.bitmap, sizeof(g_model.header.bitmap));
+      new_hash ^= hash(g_model.header.name, sizeof(g_model.header.name));
+      new_hash ^= hash(g_eeGeneral.themeName, sizeof(g_eeGeneral.themeName));
+      if (new_hash != deps_hash) {
+        deps_hash = new_hash;
         refreshBuffer();
-        memcpy(bitmapFilename, g_model.header.bitmap, sizeof(g_model.header.bitmap));
-        memcpy(modelName, g_model.header.name, sizeof(g_model.header.name));
       }
 
       if (buffer) {
@@ -78,9 +79,8 @@ class ModelBitmapWidget: public Widget
     }
 
   protected:
-    char bitmapFilename[sizeof(g_model.header.bitmap)];
-    char modelName[sizeof(g_model.header.name)];
     BitmapBuffer * buffer;
+    uint32_t deps_hash;
 };
 
 BaseWidgetFactory<ModelBitmapWidget> modelBitmapWidget("ModelBmp", NULL);
diff --git a/radio/src/maths.cpp b/radio/src/maths.cpp
index 3be1fc558..01d228cb1 100644
--- a/radio/src/maths.cpp
+++ b/radio/src/maths.cpp
@@ -99,7 +99,6 @@ int8_t calcRESXto100(int16_t x)
   return (x*25) >> 8;
 }
 #endif
-
 #if defined(HELI) || defined(FRSKY_HUB) || defined(CPUARM)
 uint16_t isqrt32(uint32_t n)
 {
@@ -172,3 +171,16 @@ void getGpsDistance()
     telemetryData.hub.maxGpsDistance = telemetryData.hub.gpsDistance;
 }
 #endif
+
+#if defined(CPUARM)
+// djb2 hash algorithm
+uint32_t hash(const void * ptr, uint32_t size)
+{
+  const uint8_t * data = (const uint8_t *)ptr;
+  uint32_t hash = 5381;
+  for (uint32_t i=0; i<size; i++) {
+    hash = ((hash << 5) + hash) + data[i]; /* hash * 33 + c */
+  }
+  return hash;
+}
+#endif
diff --git a/radio/src/opentx.h b/radio/src/opentx.h
index e85b64e04..89e099521 100644
--- a/radio/src/opentx.h
+++ b/radio/src/opentx.h
@@ -897,7 +897,7 @@ void checkModelIdUnique(uint8_t index, uint8_t module);
 #endif
 
 #if defined(CPUARM)
-
+uint32_t hash(const void * ptr, uint32_t size);
 inline int divRoundClosest(const int n, const int d)
 {
   if (d == 0)