Use of succ() and pred() functions

[FusionWolf]

Hi,

Is that common to use succ() and pred() functions when doing simple math (adding and subtracting values)?

For example for setting size of dynamic variable.



SetLength(V, Succ(Length(V)));


Versus this...



SetLength(V, Length(V) + 1);


Which one is faster?

[Sly]

Succ() and Pred() would usually be used for enumerated values.


type
TSampleEnum = (seOne, seTwo, seThree);

var
Enum: TSampleEnum;
begin
Enum := seTwo;
Enum := Succ(Enum);
end;

For the case you describe, Length(V) + 1 is definitely the more common usage.

As an aside, I read somewhere (I think it was on High Performance Delphi which is now gone), that

i := i + 1;

is faster than

Inc(i);

Mind you, I have not given this any serious testing, so it's just hearsay at the moment.

[Paulius]

As an aside, I read somewhere (I think it was on High Performance Delphi which is now gone), that
i := i + 1;
is faster than
Inc(i);

Not quite true, add operation could be faster than inc as inc cannot be pipelined, but doing a check in Delphi6 reveales that all these
i := i + 1;
Inc(i);
i:= succ(i);
generate the same code - inc.

[FusionWolf]

Okey, thanks for your answers. It seems to that I have to change my way to do things.

[Sly]

That's not to say that your usage is wrong. It is still a quite valid and legal way to do things.

[FusionWolf]

That's not to say that your usage is wrong. It is still a quite valid and legal way to do things.

Yeah sure, but I want to maximize the performance of my code (I'm programming a game with DX right now).

[Sly]

As Paulius said, all three approaches produced the same assembly code, so they are all the same speed.

[FusionWolf]

As Paulius said, all three approaches produced the same assembly code, so they are all the same speed.

Ouh. Then it doesn't matter how I code it.

[marcov]

As Paulius said, all three approaches produced the same assembly code, so they are all the same speed.

IIRC on Turbo Pascal succ() and pred() were faster, just like with TP

x:=x+1;

was slower than inc(x);

So people using succ and pred instead of +1 and -1 probably have this habit from TP times.

FPC and Delphi optimize this away, and succ and pred are now typically only useful for enumerations.