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Re: [PATCH]: Add new bytecode op `switch' for implementing branch tables

From: Stefan Monnier
Subject: Re: [PATCH]: Add new bytecode op `switch' for implementing branch tables.
Date: Fri, 10 Feb 2017 01:07:00 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.0.50 (gnu/linux)

> 1. For jump tables, HASH_TABLE_SIZE (h) == h->count, so using h->count
> directly saves the cost of an array lookup.

That doesn't invalidate the usefulness of a linear search.

> 2. Since the size equals the count, we don't need to check whether
> HASH_HASH (h, i) (the hash code) is non nil in every pass of the
> linear search loop (maphash needs to do this, before calling the
> providing function).

The linear search should compare HASH_HASH(h, i) to the search key's
hash anyway, so this comparison against nil is not needed.


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