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Old 26 September 2017, 11:40   #1
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ASM in statements - accessing "shared" variables

I'm starting to convert some of my functions to assembly and I was wondering if there was an easy way of accessing the memory locations of variables declared as "shared" at the top of the function block, and if so - how.

Thanks in advance!
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Old 26 September 2017, 18:28   #2
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Some hints from the "libsdev" archive:
A6 : Blitz keeps track of A6 to prevent it having to be unnecessarily
A5 : Blitz 2's global variable base.
A4 : Blitz 2's local variable base.
A3 : Blitz uses this to build temporary strings.
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Old 26 September 2017, 23:12   #3
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Are GetReg and PutReg what you had in mind?

GetReg d0, MyValue.l

Puts the value of MyValue in d0.

I haven't tried this, but it's worth a shot: Put the address of variable MyValue in a0:

GetReg a0, &MyValue

It should then be possible to manipulate its contents directly in memory.
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Old 27 September 2017, 04:28   #4
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Thanks guys, I'll do some more digging/experimentation.

I was thinking it may be easiest (possibly most efficient in the total number of ASM instructions?) just including the address in the function parameters? Something like

Function MyFunction{VariableAddress.l}
Move.l D0,A0
End Function

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Old 27 September 2017, 06:52   #5
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I did some tests, it seems that the best way to get a shared variable inside an ASM function is indeed to use GetReg.

This code:

Shared SharedVar.w
GetReg D0, SharedVar

Compiled to this:
MOVE.W (A5, -$7ff8),D0

Edit: Ahh.. whoops, the function also pushes the registers to the stack and pops them back afterwards, so it's not super efficient.. might still be best to pass the address in via the function's parameters.

Last edited by earok; 27 September 2017 at 07:16.
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