AVX2 optimized IVFPQ scanning code (#2253)
AVX2 optimized IVFPQ scanning code (#2253)

Summary:
Pull Request resolved: https://github.com/facebookresearch/faiss/pull/2253

add a specialized AVX2 version for IVFPQScannerT::scan_list_with_table

Reviewed By: mdouze

Differential Revision: D34733503

fbshipit-source-id: a428de04548426b39bc5a092b9f6802eadbd184d

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