LibGfx/JPEG: Don't call add_ac if not necessary

Calling it was harmless as add_ac iterates over the spectral selection, hence it won't do anything if not needed. However, this patch remains useful as it prevents dereferencing the iterator returned by find, in case the AC table isn't defined yet. This case happens with SOF2 images and is (pretty harmless as read only but still) undefined behavior.
Author: https://github.com/LucasChollet Commit: https://github.com/SerenityOS/serenity/commit/18064fdb92 Pull-request: https://github.com/SerenityOS/serenity/pull/17652 Reviewed-by: https://github.com/linusg Reviewed-by: https://github.com/nico ✅
2023-02-27 22:54:27 -05:00 · 2023-02-27 22:54:27 -05:00 · 18064fdb92 · 2024-07-17 05:09:48 +09:00
commit 18064fdb92
parent 1926a86336
1 changed files with 2 additions and 1 deletions
--- a/Userland/Libraries/LibGfx/JPEGLoader.cpp
+++ b/Userland/Libraries/LibGfx/JPEGLoader.cpp
@ -443,7 +443,8 @@ static ErrorOr<void> build_macroblocks(JPEGLoadingContext& context, Vector<Macro

                if (context.current_scan.spectral_selection_start == 0)
                    TRY(add_dc(context, block, scan_component));
-                TRY(add_ac(context, block, scan_component));
+                if (context.current_scan.spectral_selection_end != 0)
+                    TRY(add_ac(context, block, scan_component));
            }
        }
    }