From 7cbf48464e38f0edaedc32c3dec175eb9b98c7f4 Mon Sep 17 00:00:00 2001
From: Matthew McCall <m-mccall+git@outlook.com>
Date: Tue, 26 Mar 2024 16:25:01 -0400
Subject: [PATCH] Simplified Subtract::Simplify by generalizing cases for
 Exponent and Imaginary (#79)

Unbinkified code
---
 src/Subtract.cpp | 77 ++++++++++++++++--------------------------------
 1 file changed, 25 insertions(+), 52 deletions(-)

diff --git a/src/Subtract.cpp b/src/Subtract.cpp
index bbeee382..068aea61 100644
--- a/src/Subtract.cpp
+++ b/src/Subtract.cpp
@@ -19,11 +19,12 @@ Subtract<Expression>::Subtract(const Expression& minuend, const Expression& subt
 
 auto Subtract<Expression>::Simplify() const -> std::unique_ptr<Expression>
 {
-    auto simplifiedMinuend = mostSigOp ? mostSigOp->Simplify() : nullptr;
-    auto simplifiedSubtrahend = leastSigOp ? leastSigOp->Simplify() : nullptr;
+    const auto simplifiedMinuend = mostSigOp ? mostSigOp->Simplify() : nullptr;
+    const auto simplifiedSubtrahend = leastSigOp ? leastSigOp->Simplify() : nullptr;
 
-    Subtract simplifiedSubtract { *simplifiedMinuend, *simplifiedSubtrahend };
+    const Subtract simplifiedSubtract { *simplifiedMinuend, *simplifiedSubtrahend };
 
+    // 2 - 1 = 1
     if (auto realCase = Subtract<Real>::Specialize(simplifiedSubtract); realCase != nullptr) {
         const Real& minuend = realCase->GetMostSigOp();
         const Real& subtrahend = realCase->GetLeastSigOp();
@@ -31,69 +32,41 @@ auto Subtract<Expression>::Simplify() const -> std::unique_ptr<Expression>
         return std::make_unique<Real>(minuend.GetValue() - subtrahend.GetValue());
     }
 
-    if (auto ImgCase = Subtract<Imaginary>::Specialize(simplifiedSubtract); ImgCase != nullptr) {
-        return std::make_unique<Multiply<Real, Imaginary>>(Real { 2.0 }, Imaginary {});
+    // x - x = 0
+    if (simplifiedMinuend->Equals(*simplifiedSubtrahend)) {
+        return std::make_unique<Real>(Real { 0.0 });
     }
 
-    if (auto ImgCase = Subtract<Multiply<Expression, Imaginary>, Imaginary>::Specialize(simplifiedSubtract); ImgCase != nullptr) {
-        return std::make_unique<Multiply<Expression>>(
-            *(Subtract { ImgCase->GetMostSigOp().GetMostSigOp(), Real { 1.0 } }.Simplify()), Imaginary {});
-    }
-
-    if (auto ImgCase = Subtract<Imaginary, Multiply<Expression, Imaginary>>::Specialize(simplifiedSubtract); ImgCase != nullptr) {
-        return std::make_unique<Multiply<Expression>>(
-            *(Subtract { Real { 1.0 }, ImgCase->GetLeastSigOp().GetMostSigOp() }.Simplify()), Imaginary {});
-    }
-
-    if (auto ImgCase = Subtract<Multiply<Expression, Imaginary>, Multiply<Expression, Imaginary>>::Specialize(simplifiedSubtract); ImgCase != nullptr) {
-        return std::make_unique<Multiply<Expression>>(
-            *(Subtract { ImgCase->GetLeastSigOp().GetMostSigOp(), ImgCase->GetMostSigOp().GetMostSigOp() }.Simplify()), Imaginary {});
-    }
-
-    // exponent - exponent
-    if (auto exponentCase = Subtract<Exponent<Expression>, Exponent<Expression>>::Specialize(simplifiedSubtract); exponentCase != nullptr) {
-        if (exponentCase->GetMostSigOp().GetMostSigOp().Equals(exponentCase->GetLeastSigOp().GetMostSigOp()) && exponentCase->GetMostSigOp().GetLeastSigOp().Equals(exponentCase->GetLeastSigOp().GetLeastSigOp())) {
-            return std::make_unique<Real>(Real { 0.0 });
-        }
-    }
-
-    // a*exponent - exponent
-    if (auto exponentCase = Subtract<Multiply<Expression, Exponent<Expression>>, Exponent<Expression>>::Specialize(simplifiedSubtract); exponentCase != nullptr) {
-        if (exponentCase->GetMostSigOp().GetLeastSigOp().GetMostSigOp().Equals(exponentCase->GetLeastSigOp().GetMostSigOp()) && exponentCase->GetMostSigOp().GetLeastSigOp().GetLeastSigOp().Equals(exponentCase->GetLeastSigOp().GetLeastSigOp())) {
-            if (Real { 1.0 }.Equals(exponentCase->GetMostSigOp().GetMostSigOp()))
-                return std::make_unique<Real>(Real { 0.0 });
-            return std::make_unique<Multiply<Expression>>(*(Subtract { exponentCase->GetMostSigOp().GetMostSigOp(), Real { 1.0 } }.Simplify()),
-                exponentCase->GetLeastSigOp());
+    // ax - x = (a-1)x
+    if (const auto minusOneCase = Subtract<Multiply<>, Expression>::Specialize(simplifiedSubtract); minusOneCase != nullptr) {
+        if (minusOneCase->GetMostSigOp().GetLeastSigOp().Equals(minusOneCase->GetLeastSigOp())) {
+            const Subtract newCoefficient { minusOneCase->GetMostSigOp().GetMostSigOp(), Real { 1.0 } };
+            return Multiply { newCoefficient, minusOneCase->GetLeastSigOp() }.Simplify();
         }
     }
 
-    // exponent - a*exponent
-    if (auto exponentCase = Subtract<Exponent<Expression>, Multiply<Expression, Exponent<Expression>>>::Specialize(simplifiedSubtract); exponentCase != nullptr) {
-        if (exponentCase->GetLeastSigOp().GetLeastSigOp().GetMostSigOp().Equals(exponentCase->GetMostSigOp().GetMostSigOp()) && exponentCase->GetLeastSigOp().GetLeastSigOp().GetLeastSigOp().Equals(exponentCase->GetMostSigOp().GetLeastSigOp())) {
-            if (Real { 1.0 }.Equals(exponentCase->GetLeastSigOp().GetMostSigOp()))
-                return std::make_unique<Real>(Real { 0.0 });
-            return std::make_unique<Multiply<Expression>>(*(Subtract { Real { 1.0 }, exponentCase->GetLeastSigOp().GetMostSigOp() }.Simplify()),
-                exponentCase->GetMostSigOp());
+    // x-ax = (1-a)x
+    if (const auto oneMinusCase = Subtract<Expression, Multiply<>>::Specialize(simplifiedSubtract); oneMinusCase != nullptr) {
+        if (oneMinusCase->GetMostSigOp().Equals(oneMinusCase->GetLeastSigOp().GetLeastSigOp())) {
+            const Subtract newCoefficient { Real { 1.0 }, oneMinusCase->GetLeastSigOp().GetMostSigOp() };
+            return Multiply { newCoefficient, oneMinusCase->GetMostSigOp() }.Simplify();
         }
     }
 
-    // a*exponent - b*exponent
-    if (auto exponentCase = Subtract<Multiply<Expression, Exponent<Expression>>, Multiply<Expression, Exponent<Expression>>>::Specialize(simplifiedSubtract); exponentCase != nullptr) {
-        if (exponentCase->GetLeastSigOp().GetLeastSigOp().GetMostSigOp().Equals(exponentCase->GetMostSigOp().GetLeastSigOp().GetMostSigOp()) && exponentCase->GetLeastSigOp().GetLeastSigOp().GetLeastSigOp().Equals(exponentCase->GetMostSigOp().GetLeastSigOp().GetLeastSigOp())) {
-            if (Real { 1.0 }.Equals(exponentCase->GetLeastSigOp().GetMostSigOp()))
-                return std::make_unique<Real>(Real { 0.0 });
-            return std::make_unique<Multiply<Expression>>(
-                *(Subtract { exponentCase->GetMostSigOp().GetMostSigOp(), exponentCase->GetLeastSigOp().GetMostSigOp() }.Simplify()),
-                exponentCase->GetMostSigOp().GetLeastSigOp());
+    // ax-bx= (a-b)x
+    if (const auto coefficientCase = Subtract<Multiply<>>::Specialize(simplifiedSubtract); coefficientCase != nullptr) {
+        if (coefficientCase->GetMostSigOp().GetLeastSigOp().Equals(coefficientCase->GetLeastSigOp().GetLeastSigOp())) {
+            const Subtract newCoefficient { coefficientCase->GetMostSigOp().GetMostSigOp(), coefficientCase->GetLeastSigOp().GetMostSigOp() };
+            return Multiply { newCoefficient, coefficientCase->GetLeastSigOp().GetLeastSigOp() }.Simplify();
         }
     }
 
     // log(a) - log(b) = log(a / b)
-    if (auto logCase = Subtract<Log<Expression, Expression>, Log<Expression, Expression>>::Specialize(simplifiedSubtract); logCase != nullptr) {
+    if (const auto logCase = Subtract<Log<>>::Specialize(simplifiedSubtract); logCase != nullptr) {
         if (logCase->GetMostSigOp().GetMostSigOp().Equals(logCase->GetLeastSigOp().GetMostSigOp())) {
             const IExpression auto& base = logCase->GetMostSigOp().GetMostSigOp();
-            const IExpression auto& argument = Divide<Expression>({ logCase->GetMostSigOp().GetLeastSigOp(), logCase->GetLeastSigOp().GetLeastSigOp() });
-            return std::make_unique<Log<Expression>>(base, argument);
+            const IExpression auto& argument = Divide({ logCase->GetMostSigOp().GetLeastSigOp(), logCase->GetLeastSigOp().GetLeastSigOp() });
+            return std::make_unique<Log<>>(base, argument);
         }
     }