Optimal String Alignment?

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Big Red

Joined: 25 Feb 2005
Posts: 43

Big Red 30 Dec 2006, 05:50

Hey folks,

I've defined all of my project's strings with a struc macro so as to easily align them afterward. I've noticed some C compilers do so, but otherwise have no idea what such alignment is best. I don't trust C compilers too much.

I have quite a few hundred strings, and if I paragraph-align them, the DLL grows by 4000 bytes. It's a standard Win32 DLL.

Any recommendations as to what gives best overall performance? Can it be OS-dependent? (i.e., Win2k/XP/NT vs Win9x)

---------

Code:


DSTR_STRING_ALIGNMENT = whatever

struc dstr [data] {
        common

        if (DSTR_STRING_ALIGNMENT > 0)
          align DSTR_STRING_ALIGNMENT
        end if

        . db data
        .size = $ - .
        db    0
      }

30 Dec 2006, 05:50

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 31 Dec 2006, 09:14

i'd say that there is no need to align your strings at all.

31 Dec 2006, 09:14

donkey7

Joined: 31 Jan 2005
Posts: 127
Location: Poland, Malopolska

donkey7 31 Dec 2006, 12:06

i think alignment is useful when you are using widechar format (ie. aligning to word boundary).

31 Dec 2006, 12:06

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 31 Dec 2006, 12:18

donkey7: sure, i forgot that. What i meant is that natural alignment is enough (bytes unaligned, words aligned to 2, dwords to 4 etc). 16byte alignment makes sense with code, and 4096 only when the speed gain is worth of memory waste

31 Dec 2006, 12:18

Big Red

Joined: 25 Feb 2005
Posts: 43

Big Red 03 Jan 2007, 04:32

Alright then, thank you. I'll take your word for it and leave them unaligned.

03 Jan 2007, 04:32

f0dder

Joined: 19 Feb 2004
Posts: 3175
Location: Denmark

f0dder 03 Jan 2007, 06:30

If that you have long zero-terminated strings and use one of the dword-scanning strlen algorithms, 4-byte aligning the strings is a good idea. Of course an even better idea is to store string-lengths when necessary instead of doing a strlen, but that's not always possible.

03 Jan 2007, 06:30

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