From 249a20e47a7d7bcfb1cac5518b9086ad41220a4d Mon Sep 17 00:00:00 2001
From: Jonathan G Rennison <j.g.rennison@gmail.com>
Date: Wed, 8 Jun 2022 19:22:00 +0100
Subject: [PATCH] VarAction2: Add helper functions for relational comparison
 ops

---
 src/newgrf.cpp           | 12 ++++++------
 src/newgrf_spritegroup.h | 20 ++++++++++++++++++++
 2 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/src/newgrf.cpp b/src/newgrf.cpp
index ea886e575d..8a28bf60b0 100644
--- a/src/newgrf.cpp
+++ b/src/newgrf.cpp
@@ -6131,8 +6131,8 @@ static void OptimiseVarAction2Adjust(VarAction2OptimiseState &state, const GrfSp
 					if (adjust.variable == 0x1A && adjust.shift_num == 0 && group->adjusts.size() >= 2) {
 						DeterministicSpriteGroupAdjust &prev = group->adjusts[group->adjusts.size() - 2];
 						if (adjust.and_mask == 1) {
-							if (prev.operation == DSGA_OP_SLT || prev.operation == DSGA_OP_SGE || prev.operation == DSGA_OP_SLE || prev.operation == DSGA_OP_SGT) {
-								prev.operation = (DeterministicSpriteGroupAdjustOperation)(prev.operation ^ 1);
+							if (IsEvalAdjustOperationRelationalComparison(prev.operation)) {
+								prev.operation = InvertEvalAdjustRelationalComparisonOperation(prev.operation);
 								group->adjusts.pop_back();
 								state.inference = VA2AIF_SIGNED_NON_NEGATIVE | VA2AIF_ONE_OR_ZERO;
 								break;
@@ -6155,8 +6155,8 @@ static void OptimiseVarAction2Adjust(VarAction2OptimiseState &state, const GrfSp
 							if (prev.operation == DSGA_OP_OR && (prev.type == DSGA_TYPE_EQ || prev.type == DSGA_TYPE_NEQ || (prev.type == DSGA_TYPE_NONE && (prev.adjust_flags & DSGAF_SKIP_ON_LSB_SET))) && group->adjusts.size() >= 3) {
 								DeterministicSpriteGroupAdjust &prev2 = group->adjusts[group->adjusts.size() - 3];
 								bool found = false;
-								if (prev2.operation == DSGA_OP_SLT || prev2.operation == DSGA_OP_SGE || prev2.operation == DSGA_OP_SLE || prev2.operation == DSGA_OP_SGT) {
-									prev2.operation = (DeterministicSpriteGroupAdjustOperation)(prev2.operation ^ 1);
+								if (IsEvalAdjustOperationRelationalComparison(prev2.operation)) {
+									prev2.operation = InvertEvalAdjustRelationalComparisonOperation(prev2.operation);
 									found = true;
 								} else if (prev2.operation == DSGA_OP_RST && (prev2.type == DSGA_TYPE_EQ || prev2.type == DSGA_TYPE_NEQ) ) {
 									prev2.type = (prev2.type == DSGA_TYPE_EQ) ? DSGA_TYPE_NEQ : DSGA_TYPE_EQ;
@@ -6963,8 +6963,8 @@ static std::bitset<256> HandleVarAction2DeadStoreElimination(DeterministicSprite
 						DeterministicSpriteGroupAdjust &next = group->adjusts[i + 1];
 						if (next.type == DSGA_TYPE_NONE && next.operation == DSGA_OP_XOR && next.variable == 0x1A && next.shift_num == 0 && next.and_mask == 1) {
 							/* XOR: boolean invert */
-							if (prev.operation == DSGA_OP_SLT || prev.operation == DSGA_OP_SGE || prev.operation == DSGA_OP_SLE || prev.operation == DSGA_OP_SGT) {
-								prev.operation = (DeterministicSpriteGroupAdjustOperation)(prev.operation ^ 1);
+							if (IsEvalAdjustOperationRelationalComparison(prev.operation)) {
+								prev.operation = InvertEvalAdjustRelationalComparisonOperation(prev.operation);
 								erase_adjust(i + 1);
 							} else if (prev.operation == DSGA_OP_RST && (prev.type == DSGA_TYPE_EQ || prev.type == DSGA_TYPE_NEQ)) {
 								prev.type = (prev.type == DSGA_TYPE_EQ) ? DSGA_TYPE_NEQ : DSGA_TYPE_EQ;
diff --git a/src/newgrf_spritegroup.h b/src/newgrf_spritegroup.h
index 8f3061be68..c95696b8e4 100644
--- a/src/newgrf_spritegroup.h
+++ b/src/newgrf_spritegroup.h
@@ -332,6 +332,26 @@ inline DeterministicSpriteGroupAdjustOperation ReverseEvalAdjustOperation(Determ
 	}
 }
 
+inline bool IsEvalAdjustOperationRelationalComparison(DeterministicSpriteGroupAdjustOperation op)
+{
+	switch (op) {
+		case DSGA_OP_SLT:
+		case DSGA_OP_SGE:
+		case DSGA_OP_SLE:
+		case DSGA_OP_SGT:
+			return true;
+
+		default:
+			return false;
+	}
+}
+
+inline DeterministicSpriteGroupAdjustOperation InvertEvalAdjustRelationalComparisonOperation(DeterministicSpriteGroupAdjustOperation op)
+{
+	assert(IsEvalAdjustOperationRelationalComparison(op));
+	return (DeterministicSpriteGroupAdjustOperation)(op ^ 1);
+}
+
 inline bool IsEvalAdjustOperationOnConstantEffectiveLoad(DeterministicSpriteGroupAdjustOperation op, uint32 constant)
 {
 	switch (op) {