Whats the differnce between reserve data and normal data?

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shism2

Joined: 14 Sep 2005
Posts: 248

shism2 05 Mar 2006, 22:06

Whats the difference between reserve data and normal data?

Ex :

rd 1 = reserve data

Ex :

dw ? normal data

05 Mar 2006, 22:06

UCM

Joined: 25 Feb 2005
Posts: 285
Location: Canada

UCM 05 Mar 2006, 22:16

nothing, in your case.
DW stands for Define Word, RW stands for Reserve Words, but when you put a ? it indicated uninitialized data and is therefore identical.
both *can* have their contents initialized to zero, if there is initialized data after (such as dd 0 or any instruction).

05 Mar 2006, 22:16

okasvi

Joined: 18 Aug 2005
Posts: 382
Location: Finland

okasvi 05 Mar 2006, 22:22

Quote:

The data reservation directive should be followed by only one numerical
expression, and this value defines how many cells of the specified size should
be reserved. All data definition directives also accept the ? value, which
means that this cell should not be initialized to any value and the effect
is the same as by using the data reservation directive. The uninitialized
data may not be included in the output file, so its values should be always
considered unknown

from fasm.pdf

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Last edited by okasvi on 06 Mar 2006, 12:56; edited 1 time in total

05 Mar 2006, 22:22

Madis731

Joined: 25 Sep 2003
Posts: 2139
Location: Estonia

Madis731 06 Mar 2006, 09:39

...but there will be a difference if you put:

Code:

rb 1048576

Code:

times 1048576 db ?

at the end of the file. In the first case your resulting file will be small, but with the latter code you can easily add 1MB to your resulting binary.

06 Mar 2006, 09:39

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8351
Location: Kraków, Poland

Tomasz Grysztar 06 Mar 2006, 12:08

The "rb 1048576" and "times 1048576 db ?", and "db 1048576 dup ?" have all exactly the same result. The only difference is that assembler processes the "rb" faster.

06 Mar 2006, 12:08

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 06 Mar 2006, 15:52

isn't "times XXX db <something>" optimized exception?

06 Mar 2006, 15:52

Madis731

Joined: 25 Sep 2003
Posts: 2139
Location: Estonia

Madis731 06 Mar 2006, 17:40

Maybe I got it wrong then but should they be different as DB defines each byte, but RB can reserve only that byte without explicitly doing any memory-store operations on it. RB only points to the memory, while DB *ALSO* defines each byte in that region. Correct me if I'm wrong!

06 Mar 2006, 17:40

vid
Verbosity in development

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Posts: 7105
Location: Slovakia

vid 06 Mar 2006, 17:48

Madis: but defining byte with value "?" is same as reserving it

06 Mar 2006, 17:48

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8351
Location: Kraków, Poland

Tomasz Grysztar 06 Mar 2006, 19:41

"RB 1" == "DB ?"
They do exactly the same - reserve one byte as uninitialized data.

06 Mar 2006, 19:41

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 06 Mar 2006, 20:01

Tomasz: isn't "times XXX db <something>" optimized exception?

06 Mar 2006, 20:01

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8351
Location: Kraków, Poland

Tomasz Grysztar 06 Mar 2006, 20:19

No, why did you think so?

06 Mar 2006, 20:19

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 06 Mar 2006, 20:29

some times it was only way to define long initialized arrays, so it kind-of needed that. And i have some (probably false) flashbacks about you mentioning something like this optimization.

06 Mar 2006, 20:29

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