GNU bug report logs - #32503
26.1; Byte-compiled functions don't hash consistently

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Message #8 received at 32503 <at> debbugs.gnu.org (full text, mbox):

From: Tom Tromey <tom <at> tromey.com>
To: Adam Porter <adam <at> alphapapa.net>
Cc: 32503 <at> debbugs.gnu.org
Subject: Re: bug#32503: 26.1; Byte-compiled functions don't hash consistently
Date: Wed, 22 Aug 2018 19:42:12 -0600

Adam> I noticed that byte-compiled functions don't hash consistently.

The Lisp_Vectorlike case in Fequal has a number of special cases which
don't seem to be reflected in sxhash:

	if (OVERLAYP (o1))
[...]
	if (MARKERP (o1))
[...]
	if (WINDOW_CONFIGURATIONP (o1))
[...]
	/* Aside from them, only true vectors, char-tables, compiled
	   functions, and fonts (font-spec, font-entity, font-object)
	   are sensible to compare, so eliminate the others now.  */

(Bignums and bool vectors are special-cased as well but are handled in
sxhash.)  This is followed by code to loop over the pseudovector's
elements.

However, the Lisp_Vectorlike case in sxhash doesn't do any of this.

Probably there should be a rule that adding a new type should
necessitate adding a new hasher (much like how print syntax is needed);
or certainly if the type has non-trivial equal behavior.

Tom

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