From 71d49346051799f41f29be08518dda365179405d Mon Sep 17 00:00:00 2001
From: "Adam D. Ruppe" <destructionator@gmail.com>
Date: Tue, 27 May 2025 12:51:52 -0400
Subject: [PATCH] fix average filter of first line

---
 png.d | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/png.d b/png.d
index 5aa9f01..67b1e8a 100644
--- a/png.d
+++ b/png.d
@@ -2109,11 +2109,11 @@ immutable(ubyte)[] unfilter(ubyte filterType, in ubyte[] data, in ubyte[] previo
 			return assumeUnique(arr);
 		case 3:
 			auto arr = data.dup;
-			if(previousLine.length)
 			foreach(i; 0 .. arr.length) {
-				auto prev = i < bpp ? 0 : arr[i - bpp];
-				arr[i] += cast(ubyte)
-					/*std.math.floor*/( cast(int) (prev + (previousLine.length ? previousLine[i] : 0)) / 2);
+				auto left = i < bpp ? 0 : arr[i - bpp];
+				auto above = previousLine.length ? previousLine[i] : 0;
+
+				arr[i] += cast(ubyte) ((left + above) / 2);
 			}
 
 			return assumeUnique(arr);