From 112e113201a47dbca1c39d7684e25f01cfa89ac7 Mon Sep 17 00:00:00 2001
From: Gleb Mazovetskiy <glex.spb@gmail.com>
Date: Wed, 7 Aug 2024 21:28:05 +0100
Subject: [PATCH] Optimize `DoCrawl`

Benchmark:

```
cmake -S. -Bbuild-reld -G Ninja -DCMAKE_BUILD_TYPE=RelWithDebInfo -DBUILD_TESTING=ON
cmake --build build-reld --target crawl_benchmark && build-reld/crawl_benchmark
```

Before:

```
------------------------------------------------------
Benchmark            Time             CPU   Iterations
------------------------------------------------------
BM_Crawl/1        3.53 ns         3.53 ns    198384032
BM_Crawl/4        54.3 ns         54.2 ns     12907171
BM_Crawl/16        733 ns          732 ns       955101
BM_Crawl/20       1142 ns         1141 ns       613766
```

After:

```
------------------------------------------------------
Benchmark            Time             CPU   Iterations
------------------------------------------------------
BM_Crawl/1        1.36 ns         1.36 ns    453018506
BM_Crawl/4        5.59 ns         5.59 ns    124244505
BM_Crawl/16        102 ns          101 ns      6577269
BM_Crawl/20        147 ns          147 ns      4684004
```
---
 Source/crawl.cpp         | 79 +++++++++++++---------------------------
 test/crawl_benchmark.cpp |  2 +-
 2 files changed, 27 insertions(+), 54 deletions(-)

diff --git a/Source/crawl.cpp b/Source/crawl.cpp
index fe561a05b..90010f77d 100644
--- a/Source/crawl.cpp
+++ b/Source/crawl.cpp
@@ -7,66 +7,39 @@
 #include "engine/displacement.hpp"
 
 namespace devilution {
-namespace {
-
-bool CrawlFlipsX(Displacement mirrored, tl::function_ref<bool(Displacement)> function)
-{
-	for (const Displacement displacement : { mirrored.flipX(), mirrored }) {
-		if (!function(displacement))
-			return false;
-	}
-	return true;
-}
-
-bool CrawlFlipsY(Displacement mirrored, tl::function_ref<bool(Displacement)> function)
-{
-	for (const Displacement displacement : { mirrored, mirrored.flipY() }) {
-		if (!function(displacement))
-			return false;
-	}
-	return true;
-}
-
-bool CrawlFlipsXY(Displacement mirrored, tl::function_ref<bool(Displacement)> function)
-{
-	for (const Displacement displacement : { mirrored.flipX(), mirrored, mirrored.flipXY(), mirrored.flipY() }) {
-		if (!function(displacement))
-			return false;
-	}
-	return true;
-}
-
-} // namespace
 
 bool DoCrawl(unsigned radius, tl::function_ref<bool(Displacement)> function)
 {
-	if (radius == 0)
-		return function(Displacement { 0, 0 });
-
-	if (!CrawlFlipsY({ 0, static_cast<int>(radius) }, function))
-		return false;
-	for (unsigned i = 1; i < radius; i++) {
-		if (!CrawlFlipsXY({ static_cast<int>(i), static_cast<int>(radius) }, function))
-			return false;
-	}
-	if (radius > 1) {
-		if (!CrawlFlipsXY({ static_cast<int>(radius) - 1, static_cast<int>(radius) - 1 }, function))
-			return false;
-	}
-	if (!CrawlFlipsX({ static_cast<int>(radius), 0 }, function))
-		return false;
-	for (unsigned i = 1; i < radius; i++) {
-		if (!CrawlFlipsXY({ static_cast<int>(radius), static_cast<int>(i) }, function))
-			return false;
-	}
-	return true;
+	return DoCrawl(radius, radius, function);
 }
 
 bool DoCrawl(unsigned minRadius, unsigned maxRadius, tl::function_ref<bool(Displacement)> function)
 {
-	for (unsigned i = minRadius; i <= maxRadius; i++) {
-		if (!DoCrawl(i, function))
-			return false;
+	for (int r = static_cast<int>(minRadius); r <= static_cast<int>(maxRadius); ++r) {
+		if (!function(Displacement { 0, r })) return false;
+		if (r == 0) continue;
+		if (!function(Displacement { 0, -r })) return false;
+		for (int x = 1; x < r; ++x) {
+			if (!function(Displacement { -x, r })) return false;
+			if (!function(Displacement { x, r })) return false;
+			if (!function(Displacement { -x, -r })) return false;
+			if (!function(Displacement { x, -r })) return false;
+		}
+		if (r > 1) {
+			const int d = r - 1;
+			if (!function(Displacement { -d, d })) return false;
+			if (!function(Displacement { d, d })) return false;
+			if (!function(Displacement { -d, -d })) return false;
+			if (!function(Displacement { d, -d })) return false;
+		}
+		if (!function(Displacement { -r, 0 })) return false;
+		if (!function(Displacement { r, 0 })) return false;
+		for (int y = 1; y < r; ++y) {
+			if (!function(Displacement { -r, y })) return false;
+			if (!function(Displacement { r, y })) return false;
+			if (!function(Displacement { -r, -y })) return false;
+			if (!function(Displacement { r, -y })) return false;
+		}
 	}
 	return true;
 }
diff --git a/test/crawl_benchmark.cpp b/test/crawl_benchmark.cpp
index 8c47136ad..a11595601 100644
--- a/test/crawl_benchmark.cpp
+++ b/test/crawl_benchmark.cpp
@@ -8,7 +8,7 @@ namespace {
 
 void BM_Crawl(benchmark::State &state)
 {
-	const int radius = state.range(0);
+	const int radius = static_cast<int>(state.range(0));
 	for (auto _ : state) {
 		int sum;
 		Crawl(0, radius, [&sum](Displacement d) {