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Strange performance hit for insert-file-contents-literally()

From: Nordlöw
Subject: Strange performance hit for insert-file-contents-literally()
Date: Thu, 26 Nov 2009 23:58:10 -0800 (PST)
User-agent: G2/1.0

I am implementing a package for doing recursive file system magic-
detect and scan/search/grep for pattern.
In this process I have stumbled across a strange performance problem;

If I want to grep for raw binary (literal) patterns, I thought that
  (benchmark-run 1 (with-temp-buffer (buffer-disable-undo) (insert-
file-contents-literally "~/pnw.tar.gz" nil)))

would given optimal performance but it turns out that
  (benchmark-run 1 (save-excursion (set-buffer (find-file-noselect "~/
pnw.tar.gz" t t))))

is about 11 times faster on my laptop PC (the first time its called of
course, the second time it reuses the open buffer so that doesn't

As find-file-noselect() uses insert-file-contents-literally() it must
disable some stuff that find-file-literally() doesn't. The question is

I would prefer no to be forced to use find-file-noselect() as this
does other unneccessary stuff I don't need.
It also reuses the buffer if its already open which is not always what
I want with compressed files for example.
My logic namely detects the file magic headers for compressed files
and then reopens them non-literally using jka-compr in order to detect
their underlying (decompressed) type like the unix program "file"

Is this maybe a bug?

I am currently using Emacs CVS.

Thanks in advance for all tips,

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