use <random> library for RNG in Dice and include motion controller in…

… seed there are known problems with rand() and srand() (see https://en.cppreference.com/w/cpp/numeric/random/rand) and the <random> library is preferred for this reason. the function used from <random> also avoids a very rare bias that would occur using rand() and modulo, when RAND_MAX is not a multiple of d and the initially generated number falls in the last "short" segment. this commit also updates the seed to derive entropy (via seed_seq) from a mix of the system tick count and the x,y,z components of the pinetime motion controller-- taking inspiration from and with credit to @w4tsn (InfiniTimeOrg#1199)
yusufmte · Sep 19, 2022 · c1b435b · c1b435b
1 parent f0cc97c
commit c1b435b
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Showing 3 changed files with 12 additions and 5 deletions.
diff --git a/src/displayapp/DisplayApp.cpp b/src/displayapp/DisplayApp.cpp
@@ -478,7 +478,7 @@ void DisplayApp::LoadApp(Apps app, DisplayApp::FullRefreshDirections direction)
       currentScreen = std::make_unique<Screens::Steps>(this, motionController, settingsController);
       break;
     case Apps::Dice:
-      currentScreen = std::make_unique<Screens::Dice>(this);
+      currentScreen = std::make_unique<Screens::Dice>(this, motionController);
       break;
   }
   currentApp = app;

diff --git a/src/displayapp/screens/Dice.cpp b/src/displayapp/screens/Dice.cpp
@@ -30,8 +30,9 @@ namespace {
   }
 }
 
-Dice::Dice(DisplayApp* app) : Screen(app) {
-  srand(xTaskGetTickCount() % (std::numeric_limits<unsigned int>::max()));
+Dice::Dice(DisplayApp* app, Controllers::MotionController& motionController) : Screen(app) {
+  std::seed_seq sseq{xTaskGetTickCount(), static_cast<uint32_t>(motionController.X()), static_cast<uint32_t>(motionController.Y()), static_cast<uint32_t>(motionController.Z())};
+  gen.seed(sseq);
 
   nCounter.Create();
   lv_obj_align(nCounter.GetObject(), lv_scr_act(), LV_ALIGN_IN_TOP_LEFT, 0, 24);
@@ -66,11 +67,12 @@ Dice::~Dice() {
 void Dice::Roll() {
   uint8_t resultIndividual;
   uint16_t resultTotal = 0;
+  std::uniform_int_distribution<> distrib(1, dCounter.GetValue());
 
   lv_label_set_text(resultIndividualLabel, "");
 
   for (uint8_t i = 0; i < nCounter.GetValue(); i++) {
-    resultIndividual = ((rand() % dCounter.GetValue()) + 1);
+    resultIndividual = distrib(gen);
     resultTotal += resultIndividual;
     lv_label_ins_text(resultIndividualLabel, LV_LABEL_POS_LAST, std::to_string(resultIndividual).c_str());
     if (i < (nCounter.GetValue() - 1)) {
@@ -87,3 +89,4 @@ void Dice::NextColor() {
   lv_obj_set_style_local_text_color(resultTotalLabel, LV_LABEL_PART_MAIN, LV_STATE_DEFAULT, resultColors[currentColorIndex]);
   lv_obj_set_style_local_text_color(resultIndividualLabel, LV_LABEL_PART_MAIN, LV_STATE_DEFAULT, resultColors[currentColorIndex]);
 }
+
diff --git a/src/displayapp/screens/Dice.h b/src/displayapp/screens/Dice.h
@@ -3,13 +3,15 @@
 #include "displayapp/screens/Screen.h"
 #include "displayapp/widgets/Counter.h"
 #include "systemtask/SystemTask.h"
+#include <components/motion/MotionController.h>
 #include <lvgl/lvgl.h>
+#include <random>
 #include <array>
 
 namespace Pinetime::Applications::Screens {
   class Dice : public Screen {
   public:
-    Dice(DisplayApp* app);
+    Dice(DisplayApp* app, Controllers::MotionController& motionController);
     ~Dice() override;
     void Roll();
 
@@ -19,6 +21,8 @@ namespace Pinetime::Applications::Screens {
     lv_obj_t* resultTotalLabel;
     lv_obj_t* resultIndividualLabel;
 
+    std::mt19937 gen;
+
     std::array<lv_color_t, 3> resultColors = {LV_COLOR_YELLOW, LV_COLOR_MAGENTA, LV_COLOR_AQUA};
     uint8_t currentColorIndex;
     void NextColor();