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From: alexr@apple.com (Alex Rosenberg)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Pascal deficiency?
Message-ID: <47492@apple.Apple.COM>
Date: 19 Dec 90 18:27:56 GMT
References: <0B010004.o0u3z7@outpost.UUCP>
Sender: alexr@Apple.COM
Organization: Hacker's Anonymous
Lines: 68

In article <0B010004.o0u3z7@outpost.UUCP> peirce@outpost.UUCP (Michael 
Peirce) writes:
> Here are the two sources:
> 
> The Pascal Source -
> 
> UNIT Test;
> 
> INTERFACE
> 
> PROCEDURE testit(x:LONGINT);
> 
> IMPLEMENTATION
> 
> PROCEDURE SomeThing(a,b: LONGINT); EXTERNAL;
> 
> PROCEDURE Testit(x:LONGINT);
> VAR
>         i : LONGINT;
> BEGIN
>         FOR i := 1 to 10 DO BEGIN
>                 SomeThing(i,x);
>         END;
> END;
> 
> END.
> 
> And the MPW C source -
> 
> void SomeThing(int a, int b); external;
> 
> void test(int x)
> {
>         int i;
> 
>         for (i=1;i<= 10;i++) {
>                 SomeThing(i,x);
>         }
> };

The MPW C case can be optimized like:

 void test(int x)
 {
         int i;
 
         for (i=10; i; --i) {
                 SomeThing(i,x);
        }
 };

MPW C should end up using a DBRA loop for this, which uses less 
instructions. Note the predecriment, as in MPW C, prefix operations on 
register-based variables (as "i" should is) are tighter than postfix.

(Note that while I think that the Pascal compiler can generate DBRA loops,
I'm not sure it will in this case.)

By far, the handiest tool for this sort of investigation is UltraSlimFast. 
This MPW tool can be found on the System 7.0 Beta CD. It prints object 
code next to the source code, matching lines up as much as possible.

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