Can't wrap around

[LemonParty]

Hello.
I create this topic because of this problem https://forum.lazarus.freepascal.org/index.php/topic,73945.msg581824.html#msg581824.

I simplified the problem in this code:

Code: Pascal  [Select][+][-]

1. {$mode ObjFPC}{$H+}{$R-}
2.  
3. const
4.   PRIME64_1 =  Uint64(11400714785074694791);
5.   PRIME64_2 =  Uint64(14029467366897019727);
6.  
7. var
8.   a: UInt64;
9. begin
10.   a:= PRIME64_1 + PRIME64_2;
11. end.

This code not compile with error:

(10,16) Error: Overflow in arithmetic operation

Desirable to have a wrap around of values PRIME64_1 and PRIME64_2 in this situation.
Checked in trunk and 3.0.4+dfsg-22 [2019/01/24] of FPC. In both gives an error. In Lazarus 4.4 this code compiles with no problem (at least topic starter say that).

Why it doesn't wrap around in pointed versions of compiler?

[Lutz Mändle]

With FPC 3.2.2 on Linux 64bit it doesn't work either.
It gives the same error (Error: Overflow in arithmetic operation).

[Thaddy]

This is only the case when the consts are untyped, because of the internal representation of untyped consts as signed types.
But this works:

Code: Pascal  [Select][+][-]

1. {$mode ObjFPC}{$H+}
2. const
3.   PRIME64_1:Uint64 =  11400714785074694791;
4.   PRIME64_2:Uint64 =  14029467366897019727;
5.  
6. var
7.   a: UInt64;
8. begin
9.   a:= PRIME64_1 + PRIME64_2;
10. end.

[LemonParty]

Thank you for checking, Lutz Mändle.
Great Thaddy, I hope this will cure the problem.

[Martin_fr]

Thaddy's example might want a {$WriteableConst off}

Or as a workaround:

Code: Pascal  [Select][+][-]

1. {$mode ObjFPC}{$H+}{$R-}
2.  
3. const
4.   PRIME64_1 =  Uint64(11400714785074694791);
5.   PRIME64_2 =  Uint64(14029467366897019727);
6.  
7. var
8.   a: UInt64;
9. begin
10.   a:= qword(pointer( PRIME64_1) + PRIME64_2);
11. end.

I don't know, it might be worth opening an issue on this.

As for the example {$R-} is range checking. What should have been there is overflow checking {$Q-}. But that doesn't help either.

[LemonParty]

I can't for some reason create an issue on gitlab. Previously I was able to do that.

Can someone post this issue?

[LemonParty]

I successfully created an issue in bugtracker.