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From: Chris.Gehlker@p12.f56.n114.z1.fidonet.org (Chris Gehlker)
Newsgroups: comp.sys.mac.programmer
Subject: Pascal deficiency?
Message-ID: <33176.27759EC3@stjhmc.fidonet.org>
Date: 24 Dec 90 06:20:33 GMT
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AB> I generally prefer Pascal programming, but I have come up against 
AB> what seems like a real deficiency in the language. I never really 
AB> thought about it before, but there does not seem to be any equivalent 
AB> to the ++ or -- operator in Pascal. I was doing some speed checks 
AB> on array accessing today, and it occured to me that in doing 
AB> something like incrementing an entry by one, the computer was 
AB> doing rather a lot of work! 
AB> Either there is no way to do a quick increment in Pascal, or 
AB> I'm missing something in my knowledge, or I'm wrong about the 
AB> speed difference between things like ++(variable) and 
(variable):=(variable)+1

You are right about the loss of efficiency in accessing arrays but wrong about
 
the source of the inefficiency. Variable := Variable +1 or Variable := 
Succ(variable)
will generate exactly the same code as variable++, namely a addq.x  #1,Dx. 
Where Pascal falls down is in address arthmetic:
for i := 1 to rows do
     for j := 1 to columns do
          thearray[i,j] := something;
will generate a run time multiply to each time through the inner loop to 
figure
out the offset from the start of the array.  On the Mac you can work around
this by writing something like:
Type elementPtr = ^integer;

var
     theElement, arrayStart:longint;

...
arrayStart := longint(@thearray[1,1]);
theElement := 0
while theElement <= longint(@theArray[rows,columns]) do
begin
     elementPtr(arrayStart + theElement)^ := something;
     theElement := theElement + sizeof(integer)
end;
This gives a big speedup at the cost of clarity and portability. 
 

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