Re: How to quickly compare equality of structs ...

[Keith David Bershatsky <esq@lawlist.com>]

Thank you, Paul, for having a look at this particular thread.

I had read on Stackoverflow that memcmp is not always reliable, and that is why I was trying to come up with a quick and guaranteed method of doing the comparison of data for each fake cursor in the new/old caches:

https://stackoverflow.com/a/141791/2112489

In the accepted answer, it says that C provides no method for comparing equality of structs ...

My only experience with a hash table has been in Lisp by setting up a unique key per each entry in the table; e.g., make-hash-table, gethash, puthash ....  The old cache and new cache will most likely have a different number of fake cursors and the order in which they appear will also be different; e.g., 200 fake cursors in the old cache and 250 fake cursors in the new cache.  Based on my limited experience with hash tables in Lisp, I am unable to visualize how I could use such a table in C to do my comparison for each fake cursor ....

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> Date: [05-06-2019 12:00:11] <6 May 2019 12:00:11 -0700>
> From: Paul Eggert <eggert@cs.ucla.edu>
> To: Keith David Bershatsky <esq@lawlist.com>
> Cc: Emacs Devel <emacs-devel@gnu.org>
> Subject: Re: How to quickly compare equality of structs ...
> 
> On 5/6/19 11:55 AM, Keith David Bershatsky wrote:
> > PROBLEM:  If the tentative plan makes good sense, then how can I programmatically turn a combination of int, enum, double and bool into one (1) unique numeric representation such as a SHA1 (Secure Hash Algorithm)?
> 
> It's not clear to me that hashing is needed here; why not just use
> memcmp? And if you do need hashing, why not just use an ordinary hash
> table rather than messing with cryptographic hashing?