How to avoid copying

[BrunoK]

It is not cleaner if Key is a record itself

That would be (untested) :

Code: Pascal  [Select][+][-]

1. type
2.   TKey = record
3.     FTheValue: integer;
4.   end;
5.   pKey = ^TKey;
6.  
7.   TPair = record
8.     First: TKey;
9.     Second: TKey; // Some valid field
10.   end;
11.   PPair = ^TPair;
12.  
13.   function PairKeyCompare(P1, P2: Pointer): integer;
14.   var
15.     pa1: PPair absolute P1;
16.     pa2: PPair absolute P2;
17.     pk1, pk2: pKey;
18.   begin
19.     pk1 := @pa1^.First;
20.     pk2 := @pa2^.First;
21.     if pk1^.FTheValue < pk2^.FTheValue then
22.       Result := -1
23.     else if pk1^.FTheValue = pk2^.FTheValue then
24.       Result := 0
25.     else
26.       Result := 1;
27.   end;
28.  

[d2010]

Hi
@d2010: What a load of utter crap and nonsense!!!
I think you're in over your paygrade, sorry mate...
Regards Benny

If you use   inside any DLL+exe then  your source  PairKeyCompare(P1, P2: Pointer) hangup the memory of cpkunzip.dll

Code: [Select]

Library cpkunzip;
Interface
Function PairCompare(p1,p2:pointer):integer;
var
  pa1: PPair absolute P1;
  pa2: PPair absolute P2;
begin
  if pa1^.Key.First < pa2^.Key.First then Result:= -1
  else if pa1^.Key.First = pa2^.Key.First then Result:= 0
  else Result:= 1;
end;

Var boca:word=000;
Procedure ClearSource_str_Files(dir:String);
Begin
...
  boca:=ord(PairCompare(Dir1,Dir2) = 01 )*1 +
           ord(PairCompare(NamF1,Namf2)=01)*64;
...
End;

Function dfn_clear0dir(dirname:string):integer;
Begin udm_free10spincount:=00;
      odutWcMatch:='*';
      odutWcMatch:='*';
      ClearSource_str_Files(dirname);
      result:=RTGOOD;
End;
Export dfn_clear0dir;
Begin
     boca:=00;
End.
{--}


[cdbc]

Hi
@d2010: What the H*LL is this:

Code: Pascal  [Select][+][-]

1. Library cpkunzip;
2. Interface
3. Function PairCompare(p1,p2:pointer):integer;
4. var
5.   pa1: PPair absolute P1;
6.   pa2: PPair absolute P2;
7. begin
8.   if pa1^.Key.First < pa2^.Key.First then Result:= -1
9.   else if pa1^.Key.First = pa2^.Key.First then Result:= 0
10.   else Result:= 1;
11. end;
12.  
13. Var boca:word;
14. Function ClearSource_str_Files(dir:String);
15.  
16. Begin
17. ...
18.   boca:=(PairCompare(Dir1,Dir2) = 01 )*1 +
19.            (PairCompare(NamF1,Namf2)=01)*2;
20. ...
21. End;
22.  
23. Function dfn_clear0dir(dirname:string):integer;
24. Begin udm_free10spincount:=00;
25.       odutWcMatch:='*';
26.       odutWcMatch:='*';
27.       ClearSource_str_Files(dirname);
28.       result:=RTGOOD;
29. End;
30. Export dfn_clear0dir;
31. Begin
32.      boca:=f00;
33. End.
34. {--}

Do you even try to compile these 'Mushroom Dreams' of yours?!?
Oh, I know, it's Saturday and you're smokin' tha weed....
Well, then have fun mate \ö/
Regards Benny

[Amir61]

@BrunoK

What you are suggesting is equivalent of the pointer approach I described in my starting post, right?

[440bx]

Here are a couple of modified/simplified versions of @BrunoK's code:

Code: Pascal  [Select][+][-]

1. program _PointerAbsolute;
2.  
3. type
4.   TKey = record
5.     FTheValue : integer;
6.   end;
7.   pKey = ^TKey;
8.  
9.   TPair = record
10.     First   : TKey;
11.     Second  : TKey; // Some valid field
12.   end;
13.   PPair = ^TPair;
14.  
15. function PairKeyCompare1(P1, P2 : Pointer): integer;
16. var
17.   pa1    : PPair absolute P1;
18.   pa2    : PPair absolute P2;
19.  
20.   v1, v2 : integer;
21.  
22. begin
23.   { making a copy of the FTheValue fields                                     }
24.  
25.   v1 := pa1^.First.FTheValue;
26.   v2 := pa2^.First.FTheValue;
27.  
28.   if v1 < v2 then exit(-1);
29.   if v1 = v2 then exit(-0);
30.  
31.   result := 1;
32. end;
33.  
34. function PairKeyCompare2(P1, P2 : Pointer): integer;
35. var
36.   pa1    : PPair absolute P1;
37.   pa2    : PPair absolute P2;
38.  
39. begin
40.   { without making a copy                                                     }
41.  
42.   if pa1^.First.FTheValue < pa2^.First.FTheValue then exit(-1);
43.   if pa1^.First.FTheValue = pa2^.First.FTheValue then exit(-0);
44.  
45.   result := 1;
46. end;
47.  
48. var
49.   v1, v2 : TPair;
50.  
51. begin
52.   PairKeyCompare1(@v1, @v2);
53.   PairKeyCompare2(@v1, @v2);
54.  
55.   readln;
56. end.                        
57.  

Compiled with O4 (max optimization), it produces:

Code: ASM  [Select][+][-]

1. H:\Dev\Tests\00_PointerAbsolute\PointerAbsolute.lpr:27  v1 := pa1^.First.FTheValue;
2. 00000001000015D0 8B09                     mov ecx,[rcx]
3. H:\Dev\Tests\00_PointerAbsolute\PointerAbsolute.lpr:28  v2 := pa2^.First.FTheValue;
4. 00000001000015D2 8B12                     mov edx,[rdx]
5. H:\Dev\Tests\00_PointerAbsolute\PointerAbsolute.lpr:30  if v1 < v2 then exit(-1);
6. 00000001000015D4 39CA                     cmp edx,ecx
7. 00000001000015D6 7E08                     jle +$08    # $00000001000015E0 PAIRKEYCOMPARE1+16 PointerAbsolute.lpr:31
8. 00000001000015D8 B8FFFFFFFF               mov eax,$FFFFFFFF
9. 00000001000015DD C3                       ret
10.  
11. 00000001000015DE 6690                     nop
12.  
13. ; note that edx and ecx are not reloaded (they don't need to)
14.  
15. H:\Dev\Tests\00_PointerAbsolute\PointerAbsolute.lpr:31  if v1 = v2 then exit(-0);
16. 00000001000015E0 39CA                     cmp edx,ecx
17. 00000001000015E2 7504                     jnz +$04    # $00000001000015E8 PAIRKEYCOMPARE1+24 PointerAbsolute.lpr:33
18. 00000001000015E4 31C0                     xor eax,eax
19. 00000001000015E6 C3                       ret
20. 00000001000015E7 90                       nop
21. H:\Dev\Tests\00_PointerAbsolute\PointerAbsolute.lpr:33  result := 1;
22. 00000001000015E8 B801000000               mov eax,$00000001
23. H:\Dev\Tests\00_PointerAbsolute\PointerAbsolute.lpr:34  end;
24. 00000001000015ED C3                       ret
25.  
26. 00000001000015EE 0000                     add [rax],al
27.  
28. H:\Dev\Tests\00_PointerAbsolute\PointerAbsolute.lpr:44  if pa1^.First.FTheValue < pa2^.First.FTheValue then exit(-1);
29. 00000001000015F0 8B01                     mov eax,[rcx]
30. 00000001000015F2 3B02                     cmp eax,[rdx]
31. 00000001000015F4 7D06                     jnl +$06    # $00000001000015FC PAIRKEYCOMPARE2+12 PointerAbsolute.lpr:45
32. 00000001000015F6 B8FFFFFFFF               mov eax,$FFFFFFFF
33. 00000001000015FB C3                       ret
34. H:\Dev\Tests\00_PointerAbsolute\PointerAbsolute.lpr:45  if pa1^.First.FTheValue = pa2^.First.FTheValue then exit(-0);
35.  
36. ; it should use eax again instead of loading the value in ecx
37.  
38. 00000001000015FC 8B09                     mov ecx,[rcx]
39. 00000001000015FE 3B0A                     cmp ecx,[rdx]
40. 0000000100001600 7506                     jnz +$06    # $0000000100001608 PAIRKEYCOMPARE2+24 PointerAbsolute.lpr:47
41. 0000000100001602 31C0                     xor eax,eax
42. 0000000100001604 C3                       ret
43. 0000000100001605 0F1F00                   nop dword ptr [rax]
44. H:\Dev\Tests\00_PointerAbsolute\PointerAbsolute.lpr:47  result := 1;
45. 0000000100001608 B801000000               mov eax,$00000001
46. H:\Dev\Tests\00_PointerAbsolute\PointerAbsolute.lpr:48  end;
47. 000000010000160D C3                       ret
48. 000000010000160E 0000                     add [rax],al
49. H:\Dev\Tests\00_PointerAbsolute\PointerAbsolute.lpr:53  begin
50. 0000000100001610 488D6424D8               lea rsp,[rsp-$28]
51. 0000000100001615 E8B6320000               call +$000032B6    # $00000001000048D0 FPC_INITIALIZEUNITS
52. H:\Dev\Tests\00_PointerAbsolute\PointerAbsolute.lpr:54  PairKeyCompare1(@v1, @v2);
53. 000000010000161A 488D15FF090100           lea rdx,[rip+$000109FF]    # $0000000100012020
54. 0000000100001621 488D0DE8090100           lea rcx,[rip+$000109E8]    # $0000000100012010
55. 0000000100001628 E8A3FFFFFF               call -$0000005D    # $00000001000015D0 PAIRKEYCOMPARE1 PointerAbsolute.lpr:27
56. H:\Dev\Tests\00_PointerAbsolute\PointerAbsolute.lpr:55  PairKeyCompare2(@v1, @v2);
57. 000000010000162D 488D15EC090100           lea rdx,[rip+$000109EC]    # $0000000100012020
58. 0000000100001634 488D0DD5090100           lea rcx,[rip+$000109D5]    # $0000000100012010
59. 000000010000163B E8B0FFFFFF               call -$00000050    # $00000001000015F0 PAIRKEYCOMPARE2 PointerAbsolute.lpr:44
60. H:\Dev\Tests\00_PointerAbsolute\PointerAbsolute.lpr:57  readln;
61. 0000000100001640 E88B6C0000               call +$00006C8B    # $00000001000082D0 fpc_get_input
62. 0000000100001645 4889C1                   mov rcx,rax
63. 0000000100001648 E873710000               call +$00007173    # $00000001000087C0 FPC_READLN_END
64. 000000010000164D E8DE310000               call +$000031DE    # $0000000100004830 FPC_IOCHECK
65. H:\Dev\Tests\00_PointerAbsolute\PointerAbsolute.lpr:58  end.
66. 0000000100001652 E889360000               call +$00003689    # $0000000100004CE0 FPC_DO_EXIT
67. 0000000100001657 90                       nop
68. 0000000100001658 488D642428               lea rsp,[rsp+$28]
69. 000000010000165D C3                       ret
70.  

The code generated using a copy is faster (and better) than the code generated without using a copy.