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pmcgee

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  1. To be fair, there's a Catch-22 in that idea. ie don't implement Generics until you have experience implementing Generics. (and the same would apply for trying to use a c++ like move feature) If someone publishes open source ... not part of a (reasonably big) commercial product like RAD ... and it is useful to maybe 80% of people, then sure it's valuable to point out edge cases - but it doesn't mean it should be discouraged. We need *more* Delphi out there. And more understanding of these elements that weren't even part of Delphi in say 2005.
  2. Sure ... byte / ansichar is a simple case ... but you need to start with simple and solve it the best you can before tackling a bigger / harder problem. The testing is made faster by just using a shorter string. The increase in time is about x10 at the 12 mark ... so 11 is quicker, and 10 is almost immediate.
  3. I'm a little confused. First post *is* the Delphi code. I've been learning about C++ for a couple years, alongside 20 with Delphi, and the ideas from both are interesting to me. Naively, it seems like a Delphi version should be able to produce about the same performance. Teasing that out should be educational.
  4. The calling code from c++ : int main() { const std::string Test = "abcdefghijkl"; int i = 0; std::string v = Test; Timer timer; timer.start(); do { ++i; } while ( std::next_permutation( v.begin(), v.end() ) ); timer.stop(); std::cout << "C++ " << i << "\n"; std::cout << "Seconds: " << timer.elapsedSeconds() << std::endl; AnsiString s = Test.c_str(); int len = s.Length()+1; i = 0; Timer timer2; timer2.start(); do { ++i; } while ( D_next_permutation(s, 1, len ) ); timer2.stop(); std::cout << "Delphi " << i << "\n"; std::cout << "Seconds: " << timer2.elapsedSeconds() << std::endl; getchar(); return 0;
  5. @Kas Ob. posted this in the original thread : procedure reverse2(var s: AnsiString; const a, x: word); inline; var i, j: word; tmpChar: Byte; SBytes: pByte absolute s; begin if a = x - 1 then exit; j := (x - a) shr 1; // trunc((x-a)/2); for i := 1 to j do begin tmpChar := SBytes[a - 1 + i]; SBytes[a - 1 + i] := SBytes[x - i]; SBytes[x - i] := tmpChar; end; end; var st: AnsiString; i: Integer; D: Uint64; begin st := '1234567890ab'; Writeln(st); d := GetTickCount; for i := 1 to 479001600 do // 12! reverse(st, 1, 12); D := GetTickCount - D; Writeln(d); st := '1234567890ab'; Writeln(st); d := GetTickCount; for i := 1 to 479001600 do reverse2(st, 1, 12); D := GetTickCount - D; Writeln(d); Readln; end. With these results ... (32 bit? 64 bit? compile) 1234567890ab 14125 1234567890ab 4891
  6. I didn't recall correctly. This was a significant speed up : procedure swapByte( a:Pbyte ; b:Pbyte ); inline; begin if a <> b then begin a^ := a^ + b^; b^ := a^ - b^; a^ := a^ - b^ ; end; end; swapByte( @s[a-1+i] , @s[x_-i] );
  7. A bit of a challenge ... to produce Delphi code equaling the performance of C++'s next_permutation. Hopefully more readable in Delphi ... unit D_Next_perm_string; interface procedure swapCh(var a:Ansichar; var b:Ansichar); procedure reverse(var s:AnsiString; const a,x:word); function D_next_permutation(var s:AnsiString; const first, end_:word) : boolean; implementation //uses System.Diagnostics; procedure swapCh( var a : Ansichar; var b : Ansichar ); inline; var c : Ansichar; begin if a<>b then begin c := a; a := b; b := c; end; end; procedure reverse(var s:AnsiString; const a,x:word); inline; var i,j : word; //t : string; begin // x is one past the end of string if a = x-1 then exit; j := ( x-a ) shr 1; //trunc((x-a)/2); for i := 1 to j do swapCh( s[a-1+i] , s[x-i] ); end; function D_next_permutation(var s : AnsiString; const first, end_ : word) : boolean; inline; var i, ii, j : word; begin if first = end_ then begin result := false; exit; end; i := first + 1; if i = end_ then begin result := false; exit; end; i := end_ - 1; while true do begin ii := i; dec(i); if s[i] < s[ii] then begin j := end_; repeat dec(j); until s[i] < s[j]; swapCh( s[i] , s[j] ); reverse(s, ii, end_); result := true; exit; end; if i = first then begin reverse(s, first, end_); result := false; exit; end; end; end; end. Ballpark, we're looking at about 6s vs 2s for s = "abcdefghijkl" (12 bytes). Increases by about a factor of 10 per character beyond that. Note the c++ end() iterator is **one past the end of string**, so ... D_next_permutation(s,1,13)
  8. Maybe this is OT for this thread. I'll look up where to start a new one, and add a link.
  9. I had tried a couple things there ... this was a small improvement. I haven't pulled apart the assembly code yet. It's just an ongoing interest. It'll be fun to try it with char/byte array. procedure swapByte( a:Pbyte ; b:Pbyte ); inline; begin if a <> b then begin a^ := a^ + b^; b^ := a^ - b^; a^ := a^ - b^ ; end; end; procedure swapChar( var a : Ansichar; var b : Ansichar ); inline; var c : Ansichar; begin if a<>b then begin c := a; a := b; b := c; end; end;
  10. Just checking ... You can characterise one edge by one TPoint? or one edge by 4 TPoints? or does Fedges describe a parallelogram? Is ok. "GEORect". I get it. (I'm not sure 'edges' is the best name) ... (also ... can't see how to delete posts.)
  11. I came across this trying to duplicate C++'s std::next_permutation using Delphi. I went through various modifications, and had left a string declaration in where it was no longer needed: procedure reverse(var s:AnsiString; const a,x:word); inline; var i,j : word; //t : string; begin // x is one past the end of string if a = x-1 then exit; j := ( x-a ) shr 1; // trunc((x-a)/2); for i := 1 to j do swapCh( s[a-1+i] , s[x-i] ); end; All permutations of 12 chars = 479,001,600. C++ = 2s. Commenting out the string reduced the Delphi code from 9s to 6s. (I haven't been back to it since then.)
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