why are absolute addresses better?

The source of lzma / 7zip contains filters that transform relative
addresses in CALL-statements to absolute addresses. It is claimed
that this gives better compression. I was able to verify this
experimentally for ARM binaries, even for delta-compression.

Could sombody explain WHY absolute addresses are better? (Intuitively I
would have expected the opposite).

Regards,

-ulrich

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Ulrich Lauther          ph: +49 89 636 48834 fx: ... 636 42284
Siemens CT SE 6         Internet: Ulrich.Lauther@siemens.com

Ulrich wrote:
) The source of lzma / 7zip contains filters that transform relative
) addresses in CALL-statements to absolute addresses. It is claimed
) that this gives better compression. I was able to verify this
) experimentally for ARM binaries, even for delta-compression.
)
) Could sombody explain WHY absolute addresses are better? (Intuitively I
) would have expected the opposite).

Why would you expect relative addresses to compress better ?  With absolute
addresses, one would expect a lot of them to be the same, and therefore
compress better.


SaSW, Willem
--
Disclaimer: I am in no way responsible for any of the statements
made in the above text. For all I know I might be
drugged or something..
No I'm not paranoid. You all think I'm paranoid, don't you !
#EOT

Willem <willem@stack.nl> wrote:
: Ulrich wrote:
: ) The source of lzma / 7zip contains filters that transform relative
: ) addresses in CALL-statements to absolute addresses. It is claimed
: ) that this gives better compression. I was able to verify this
: ) experimentally for ARM binaries, even for delta-compression.
: )
: ) Could sombody explain WHY absolute addresses are better? (Intuitively I
: ) would have expected the opposite).

: Why would you expect relative addresses to compress better ?  With absolut
e
: addresses, one would expect a lot of them to be the same, and therefore
: compress better.

In "normal" compression, because I would expect small values, i.e. many
leading zeros in addresses; in delta compression, because a relative
address may be invariant when pieces of codes are moved around.

However, your reasoning makes a lot of sense.

-ulrich
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Ulrich Lauther          ph: +49 89 636 48834 fx: ... 636 42284
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