[CLOSED] Optimization at function TFPReaderBMP.ShiftCount
lazarus / 64-FPC development

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lagprogramming · 2024-01-09 11:43

packages/fcl-image/src/fpreadbmp.pp has
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
TFPReaderBMP.ShiftCount(Mask : longword) : shortint;var tmp :
shortint;begin  tmp:=0;  if Mask=0 then  begin    Result:=0;    exit; 
end;   while (Mask mod 2)=0 do { rightmost bit is 0 }  begin   
inc(tmp);    Mask:= Mask shr 1;  end;  tmp:=tmp-(8-popcnt(byte(Mask
and $FF)));  Result:=tmp;end;
The following patch replaces "while (Mask mod 2)=0 do" with the faster
"while (Mask and 1)=0 do" line.

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Zvoni · 2024-01-09 12:04

Addition:
1) Line 16+17 can be coalesced into one line
2) Why use a tmp-var in the first place?

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RayoGlauco · 2024-01-09 12:28

My own version may be like this (I agree Zvoni's opinion):

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i    
function TFPReaderBMP.ShiftCount(Mask : longword) : shortint;   
begin      Result:=0;      if Mask=0 then        exit;           while
(Mask and 1)=0 do { rightmost bit is 0 }      begin       
inc(Result);        Mask:= Mask shr 1;      end;      Result:=
Result-(8-popcnt(byte(Mask and $FF)));    end;

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AlexTP · 2024-01-10 14:49

Posted and applied:
https://gitlab.com/freepascal.org/fpc/source/-/issues/40590