Re: [PATCH v3 06/10] xdiff: split xrecord_t.ha into line_hash and minimal_perfect_hash

>
> "Ezekiel Newren via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
> > To make this clearer, the old ha field has been split:
> >   * line_hash: a straightforward hash of a line, independent of any
> >     external context. Its type is uint64_t, as it comes from a fixed
> >     width hash function.
> >   * minimal_perfect_hash: Not a new concept, but now a separate
> >     field. It comes from the classifier's general-purpose hash table,
> >     which assigns each line a unique and minimal hash across the two
> >     files. A size_t is used here because it's meant to be used to
> >     index an array. This also this avoids ` as usize` casts on the Rust
> >     side when using it to index a slice.
>
> How much extra memory pressure does this change cause?  In a single
> instance of xrecord_t, we used to have a single ulong plus a pointer
> and a size_t; now we replaced the single ulong with two 8-byte words,
> so 33% more memory per record, which is not so huge a deal?

> >  static int xdl_classify_record(unsigned int pass, xdlclassifier_t *cf, xrecord_t *rec) {
> > -     long hi;
> > +     size_t hi;
> >       xdlclass_t *rcrec;
> >
> > -     hi = (long) XDL_HASHLONG(rec->ha, cf->hbits);
> > +     hi = XDL_HASHLONG(rec->line_hash, cf->hbits);
>
> Very nice that we can lose these random-looking casts.