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While micro-optimizations are interesting, there are two questions left unanswered:

- Does this change noticeably affect the total runtime? The checksum seems simple enough that the slight difference here wouldn't show up in PNG benchmarks.

- The proposed solution uses AVX2, which is not currently used in the original codebase. Would any other part of the processing benefit from using newer instructions?

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If checksum calculation was any substantial portion of image decoding, I think that would be a strong case for simply not checking the checksum.

If you put corrupted data into a PNG decoder, I don't think it's awfully important to most users whether they get a decode error or a garbled image out.

This was actually considered, and other libraries do ignore checksums, or at least have options to:

https://github.com/richgel999/fpng/issues/9

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