SWAP and GlobalAlloc/HeapAlloc

[Dominic Mitchell]

TYPE KEYWORDEX      ' kwdx
  cbName AS BYTE                    ' Count of bytes in keyword name
  bType   AS BYTE                   ' Type of keyword
  szName  AS ASCIIZ * 64            ' Keyword name
END TYPE

The following shows how the UDT shown above is used. Memory is allocated
using GlobalAlloc.
<256*4-bytes jump table><256*4-bytes count table><keyword count * SIZEOF(KEYWORDEX)>

LOCAL ptkwdx AS KEYWORDEX PTR

lpTbl = GlobalAlloc(%GMEM_FIXED OR %GMEM_ZEROINIT, 2048 + 2000 * SIZEOF(tkwdx))
ptkwdx = lpTbl + 2048

The errata on SWAP says that it can be used to swap the target values of pointers
and that this applies to PB/DLL 6.0 & PB/CC 2.0. However, the following produces
bad data on PB/DLL 5.0.

SWAP @ptkwd[1].szName, @ptkwd[3].szName

Just wondering if this was fixed in version 6.

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Dominic Mitchell

[Semen Matusovski]

Dominic --
works (but as I remember, SWAP is not fast operation. Allocates temporary string ?)

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E-MAIL: [email protected]

[Eric Pearson]

> SWAP is not fast operation. Allocates temporary string

No, when used with strings SWAP swaps the string pointers/handles, not the string data. It's very fast!

-- Eric

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Perfect Sync Development Tools
Perfect Sync Web Site
Contact Us: mailto:[email protected][email protected]</A>

[Semen Matusovski]

Eric --
we are both do not use exact termins.
Dynamic strings - I can agree w/o test, because PB compile is enough clever.
Fixed-length strings / Asciiz - I am not ready to agree (at least, w/o test)

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E-MAIL: [email protected]

[Tom Hanlin]

Dominic, if you can show us a full example, we can look into it for you.
Or send it to mailto:[email protected][email protected]</A> .

Semen, SWAP is not necessarily the fastest technique for items involving
just a few bytes. It probably uses something like a REP MOVSx in many
cases, which imposes a bit of start-up overhead. This is not likely
to be an issue unless you need to swap an awful lot of very small items
very quickly.


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Tom Hanlin
PowerBASIC Staff

[Dominic Mitchell]

It's no big deal. I normally don't use SWAP on that type of data because
of the old description in the docs. I usually code the functions that handle
that type of data in inline assembler.
It works in PB/DLL6 so I will not pursue the matter any further.

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Dominic Mitchell