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Index > DOS > Optimising Turbo Pascal V3.01a?

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prino



Joined: 24 Jun 2004
Posts: 20
prino
Admittedly, it has nothing to do with the thread about PSR Invaders, but I've recently found a pretty well commented IDA disassembly of this compiler (I still have a few way out-of-date legal copies of IDA), and as I'm currently working with TP3 sources, I thought it might be interesting to see if this compiler can be optimised a bit.

It might no longer run on an 8086, and it might not even run under DOSemu or VDosPlus, but it would definitely run under DOS in a VM, or XP in the same.

There are obviously plenty of simple optimisations to be made, like replacing
Code:
mov cl, immediate
shr ax, cl    

by
Code:
shr ax, immediate    

but what about merging Norbert Juffa's improved "6-byte real" arithmetic from TPL60N19 or BPL70N16 into TP3, and the like?

If anyone is interested, feel free to reply here, or drop me a line, and I can forward the assembler listing produced by IDA, cannot attach a zipped copy right now, as the Freeware IDA 7.0 on my laptop doesn't want to know about IDA 4.x .IDB files.

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Robert AH Prins
robert dot ah dot prins at the big account from Google Wink
Post 11 Jul 2020, 12:53
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17662
Location: In your JS exploiting you and your system
revolution
What are you optimising for? Speed? Size? Other?
Post 11 Jul 2020, 13:28
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prino



Joined: 24 Jun 2004
Posts: 20
prino
Given that the average CPU nowadays runs at GHz speeds, and Turbo was already, relatively speaking, insanely fast on a 4.77MHz PC, speed isn't really too much of a problem, although fewer instructions emulated helps a (very tiny) bit.

Size seems to be the main thing, there is plenty of code where "6 pushes, a call, 6 pops" could be replaced by a single, albeit probably somewhat slower, "PUSHA/POPA", but the other area, retrofitting (Norbert Juffa's) TP6/BP7 code would be far more interesting, as that would make the 6-byte real code IEEE-754 compliant (well, as far as the format allows), and it should allow comparing output of this compiler with that of Virtual Pascal or FreePascal.

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Robert AH Prins
robert dot ah dot prins at the big account from Google Wink
Post 11 Jul 2020, 13:40
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