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facebookresearch / faiss

A library for efficient similarity search and clustering of dense vectors.

Home Page:https://faiss.ai

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faiss/impl/index_write.cpp code

LIZHICHAOUNICORN opened this issue · comments

commented 
//  main branch,  faiss/impl/index_write.cpp:392
if (const IndexFlat* idxf = dynamic_cast<const IndexFlat*>(idx)) {
        uint32_t h =
                fourcc(idxf->metric_type == METRIC_INNER_PRODUCT ? "IxFI"
                               : idxf->metric_type == METRIC_L2  ? "IxF2"
                                                                 : "IxFl");
        WRITE1(h);
        write_index_header(idx, f);
        WRITEXBVECTOR(idxf->codes);
    } else if (const IndexLSH* idxl = dynamic_cast<const IndexLSH*>(idx)) {
        uint32_t h = fourcc("IxHe");
        WRITE1(h);
        write_index_header(idx, f);
        WRITE1(idxl->nbits);
        WRITE1(idxl->rotate_data);
        WRITE1(idxl->train_thresholds);
        WRITEVECTOR(idxl->thresholds);
        int code_size_i = idxl->code_size;
        WRITE1(code_size_i);
        write_VectorTransform(&idxl->rrot, f);
        WRITEVECTOR(idxl->codes);
       ...
}

Why the if condition statement use "=" ?

commented

I am not expert, but when you are doing dynamic cast, you checking if you have right object in variable idx, and to do that you must add dynamic cast to variable. https://www.youtube.com/watch?v=TM-U6m47i5w I hope i was helpful.