Tests/test_file_avif.py::TestFileAvif::test_write_rgb fails on riscv64

[felixonmars]

What did you do?

Running the test suite of Pillow on Arch Linux riscv64, libavif 1.4.1 and aom 3.13.3. I can confirm they pass on x86_64 with the same setup.

What did you expect to happen?

Tests pass.

What actually happened?

a = <PIL.AvifImagePlugin.AvifImageFile image mode=RGB size=128x128 at 0x3F7DD3F770>
b = <PIL.PngImagePlugin.PngImageFile image mode=RGB size=128x128 at 0x3F88BCF610>
epsilon = 6.88, msg = None        

    def assert_image_similar(
        a: Image.Image, b: Image.Image, epsilon: float, msg: str | None = None
    ) -> None:
        assert a.mode == b.mode, msg or f"got mode {repr(a.mode)}, expected {repr(b.mode)}"
        assert a.size == b.size, msg or f"got size {repr(a.size)}, expected {repr(b.size)}"
    
        a, b = convert_to_comparable(a, b)
    
        diff = 0
        for ach, bch in zip(a.split(), b.split()):
            chdiff = ImageMath.lambda_eval(
                lambda args: abs(args["a"] - args["b"]), a=ach, b=bch
            ).convert("L")
            diff += sum(i * num for i, num in enumerate(chdiff.histogram()))
    
        ave_diff = diff / (a.size[0] * a.size[1])
        try:
>           assert epsilon >= ave_diff, (
                (msg or "")
                + f" average pixel value difference {ave_diff:.4f} > epsilon {epsilon:.4f}"
            )
E           AssertionError:  average pixel value difference 6.9274 > epsilon 6.8800
E           assert 6.88 >= 6.92742919921875

Tests/helper.py:129: AssertionError

What are your OS, Python and Pillow versions?

• OS: Arch Linux riscv64
• Python: 3.14.4
• Pillow: 12.2.0

$ python3 -m PIL.report
--------------------------------------------------------------------
Pillow 12.2.0
Python 3.14.4 (main, Apr 24 2026, 21:37:53) [GCC 15.2.1 20260209]
--------------------------------------------------------------------
Python executable is /usr/bin/python3
System Python files loaded from /usr
--------------------------------------------------------------------
Python Pillow modules loaded from /usr/lib/python3.14/site-packages/PIL
Binary Pillow modules loaded from /usr/lib/python3.14/site-packages/PIL
--------------------------------------------------------------------
--- PIL CORE support ok, compiled for 12.2.0
--- TKINTER support ok, loaded 8.6
--- FREETYPE2 support ok, loaded 2.14.3
--- LITTLECMS2 support ok, loaded 2.19
--- WEBP support ok, loaded 1.6.0
--- AVIF support ok, loaded 1.4.1
--- JPEG support ok, compiled for libjpeg-turbo 3.1.4.1
--- OPENJPEG (JPEG2000) support ok, loaded 2.5.4
--- ZLIB (PNG/ZIP) support ok, loaded 1.3.2
--- LIBTIFF support ok, loaded 4.7.1
--- RAQM (Bidirectional Text) support ok, loaded 0.10.5
--- LIBIMAGEQUANT (Quantization method) support ok, loaded 4.2.2
--- XCB (X protocol) support ok
--------------------------------------------------------------------

[radarhere]

I've created #9606