From fa75ab404f065670671a614c7839a3f963ef352b Mon Sep 17 00:00:00 2001
From: Jordan Woyak <jordan.woyak@gmail.com>
Date: Sun, 30 Dec 2018 19:50:20 -0600
Subject: [PATCH] ExpressionParser: operator precedence.

---
 .../ControlReference/ExpressionParser.cpp     | 80 ++++++++++++-------
 1 file changed, 51 insertions(+), 29 deletions(-)

diff --git a/Source/Core/InputCommon/ControlReference/ExpressionParser.cpp b/Source/Core/InputCommon/ControlReference/ExpressionParser.cpp
index 4d68a090d8..a5c4036167 100644
--- a/Source/Core/InputCommon/ControlReference/ExpressionParser.cpp
+++ b/Source/Core/InputCommon/ControlReference/ExpressionParser.cpp
@@ -139,7 +139,7 @@ public:
       return '\'' + data + '\'';
     case TOK_VARIABLE:
       return '$' + data;
-    case TOK_INVALID:
+    default:
       break;
     }
 
@@ -528,7 +528,7 @@ public:
   ControlState GetValue() const override
   {
     constexpr int MAX_REPS = 10000;
-    constexpr int COND_THRESHOLD = 0.5;
+    constexpr ControlState COND_THRESHOLD = 0.5;
 
     // Returns 1.0 on successful loop, 0.0 on reps exceeded. Sensible?
 
@@ -543,7 +543,7 @@ public:
     return 0.0;
   }
   void SetValue(ControlState value) override {}
-  std::string GetFuncName() const override { return "Sin"; }
+  std::string GetFuncName() const override { return "While"; }
 };
 
 std::unique_ptr<UnaryExpression> MakeUnaryExpression(std::string name,
@@ -782,22 +782,13 @@ private:
     }
   }
 
-  bool IsUnaryExpression(TokenType type)
-  {
-    switch (type)
-    {
-    case TOK_UNARY:
-      return true;
-    default:
-      return false;
-    }
-  }
+  static bool IsUnaryExpression(TokenType type) { return TOK_UNARY == type; }
 
   ParseResult Unary()
   {
     if (IsUnaryExpression(Peek().type))
     {
-      Token tok = Chew();
+      const Token tok = Chew();
       ParseResult result = Atom();
       if (result.status == ParseStatus::SyntaxError)
         return result;
@@ -807,29 +798,60 @@ private:
     return Atom();
   }
 
-  bool IsBinaryToken(TokenType type)
+  static bool IsBinaryToken(TokenType type)
   {
     return type >= TOK_BINARY_OPS_BEGIN && type < TOK_BINARY_OPS_END;
   }
 
-  ParseResult Binary()
+  static int BinaryOperatorPrecedence(TokenType type)
   {
-    ParseResult result = Unary();
-    if (result.status == ParseStatus::SyntaxError)
-      return result;
-
-    std::unique_ptr<Expression> expr = std::move(result.expr);
-    while (IsBinaryToken(Peek().type))
+    switch (type)
     {
-      Token tok = Chew();
-      ParseResult unary_result = Unary();
-      if (unary_result.status == ParseStatus::SyntaxError)
+    case TOK_MUL:
+    case TOK_DIV:
+    case TOK_MOD:
+      return 1;
+    case TOK_ADD:
+    case TOK_SUB:
+      return 2;
+    case TOK_GTHAN:
+    case TOK_LTHAN:
+      return 3;
+    case TOK_AND:
+      return 4;
+    case TOK_OR:
+      return 5;
+    case TOK_COND:
+    case TOK_ASSIGN:
+      return 6;
+    case TOK_COMMA:
+      return 7;
+    default:
+      assert(false);
+      return 0;
+    }
+  }
+
+  ParseResult Binary(int precedence = 999)
+  {
+    ParseResult lhs = Unary();
+
+    if (lhs.status == ParseStatus::SyntaxError)
+      return lhs;
+
+    std::unique_ptr<Expression> expr = std::move(lhs.expr);
+
+    // TODO: handle LTR/RTL associativity?
+    while (IsBinaryToken(Peek().type) && BinaryOperatorPrecedence(Peek().type) < precedence)
+    {
+      const Token tok = Chew();
+      ParseResult rhs = Binary(BinaryOperatorPrecedence(tok.type));
+      if (rhs.status == ParseStatus::SyntaxError)
       {
-        return unary_result;
+        return rhs;
       }
 
-      expr = std::make_unique<BinaryExpression>(tok.type, std::move(expr),
-                                                std::move(unary_result.expr));
+      expr = std::make_unique<BinaryExpression>(tok.type, std::move(expr), std::move(rhs.expr));
     }
 
     return {ParseStatus::Successful, std::move(expr)};
@@ -851,7 +873,7 @@ private:
   }
 
   ParseResult Toplevel() { return Binary(); }
-};
+};  // namespace ExpressionParser
 
 static ParseResult ParseComplexExpression(const std::string& str)
 {