From 4e3a3b312c946bed572e4c1a05314ddd673c3389 Mon Sep 17 00:00:00 2001
From: Michele Bini <michele.bini@gmail.com>
Date: Fri, 10 Jun 2022 20:03:45 +0200
Subject: Clarify code a bit


diff --git a/src/displayapp/screens/Calculator.cpp b/src/displayapp/screens/Calculator.cpp
index c0a947d..c44f781 100644
--- a/src/displayapp/screens/Calculator.cpp
+++ b/src/displayapp/screens/Calculator.cpp
@@ -10,11 +10,8 @@ using namespace Pinetime::Applications::Screens;
 
 // Anonymous Namespace for all the structs
 namespace {
-  struct Node {
-    char op;
-    double val;
-  };
-  template <typename X, uint8_t max_stack_len> struct StaticallyAllocatedStack {
+  template <typename X, uint8_t max_stack_len> struct Stack {
+    // Basic stack data type without dynamic allocations
     X data[max_stack_len];
     uint8_t stack_len = 0;
     inline auto   size()   { return stack_len;                }
@@ -25,8 +22,13 @@ namespace {
     inline X&  push()   { return data[stack_len++];        }
     inline void push(X x) { X& datum{ push() }; datum = x; }
   };
-  template <uint8_t max_stack_len> struct CalcStack : public StaticallyAllocatedStack<Node, max_stack_len> {
-    typedef StaticallyAllocatedStack<Node, max_stack_len> Super;
+  struct Node {
+    // if op == 0, the node represents a double value, otherwise it's an operator
+    char op;
+    double val;
+  };
+  template <uint8_t max_stack_len> struct CalcStack : public Stack<Node, max_stack_len> {
+    typedef Stack<Node, max_stack_len> Super;
     inline Node& push() { return Super::push(); }
     inline void pushValue(double value) {
       Super::data[Super::stack_len].op = 0;
@@ -37,6 +39,8 @@ namespace {
       Node* node0 = Super::data + Super::stack_len;
       node0->op = op;
       if (Super::stack_len > 1) {
+        // Evaluate subexpressions as soon as it's possible
+        // Inf and NaN take care of error handling in case of non-finite results
         Node* node1 = node0 - 1;
         if (node1->op == 0) {
           Node* node2 = node1 - 1;
@@ -73,7 +77,7 @@ namespace {
     }
   };
 
-  template <typename I, typename F, typename S> bool parseFloat(I& i, F& f, S& s) {
+  template <typename Input, typename Float, typename Sign> bool parseFloat(Input& i, Float& f, Sign& s) {
     f = 0;
     int8_t dot_position = -1;
     while (!i.empty()) {
@@ -171,12 +175,12 @@ Calculator::Calculator(DisplayApp* app, Controllers::MotorController& motorContr
 }
 
 void Calculator::Eval() {
-  StaticallyAllocatedStack<char, 32> input;
+  Stack<char, 32> input;
   for (int8_t i = position - 1; i >= 0; i--) {
     input.push(text[i]);
   }
   CalcStack<16> output;
-  StaticallyAllocatedStack<char, 32> operators;
+  Stack<char, 32> operators;
   bool expectingNumber = true;
   int8_t sign = +1;
   double resultFloat;
@@ -284,18 +288,6 @@ void Calculator::Eval() {
   }
   // perform the calculation
   resultFloat = output.top().val;
-#if 0
-  // This only seems to work in the simulator
-  if (!std::isfinite(resultFloat)) {
-    goto eval_error;
-  }
-  position = 0;
-  for (char s : std::to_string(resultFloat)) {
-    text[position++] = s;
-  }
-  text[position] = 0;
-#else
-  // position = snprintf(text, 20, "%.9g", resultFloat);
   // make sure that the absolute value of the integral part of result fits in a 32 bit unsigned integer
   sign = (resultFloat < 0);
   if (sign) {
@@ -326,7 +318,6 @@ void Calculator::Eval() {
       position--;
     }
   }
-#endif
   return;
  eval_error:
   motorController.RunForDuration(10);
-- 
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