Improvement of BIRegularMultiply
lazarus / 64-FPC development

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lagprogramming · 2024-03-22 11:40

packages/fcl-hash/src/fptlsbigint.pas 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
BIRegularMultiply(var Context: TBigIntContext; BIA, BIB: PBigInt;
InnerPartial, OuterPartial: Integer): PBigInt;var  Carry:
TBIComponent;  BIR: PBigInt;  I, J, N, RIndex, T: Integer;  SA, SB,
SR:PBIComponent;  Tmp: TBILongComponent;begin  if not BICheck(BIA^) or
not BICheck(BIB^) then  begin    Result:=nil;    Exit;  end;  I := 0; 
N := BIA^.Size;  T := BIB^.Size;  BIR := BIAllocate(Context, N+T);  SR
:= BIR^.Components;  SA := BIA^.Components;  SB := BIB^.Components; 
FillByte(BIR^.Components^, (N+T) * BIGINT_COMP_BYTE_SIZE, 0);  repeat 
  Carry := 0;    RIndex := I;    J := 0;    if (OuterPartial > I) and
(OuterPartial < N) then    begin      RIndex := OuterPartial-1;      J
:= OuterPartial-I-1;    end;    repeat      if (InnerPartial > 0) and
(RIndex >= InnerPartial) then        Break;      Tmp :=
TBILongComponent(SR[RIndex]) + TBILongComponent(SA[J]) * SB[I] +
Carry; // Avoid overflow      SR[RIndex] := TBIComponent(Tmp and
$ffffffff); // Downsize      Inc(RIndex);      Carry := Tmp shr
BIGINT_COMP_BIT_SIZE;      Inc(J);    until J >= N;    SR[RIndex] :=
Carry;    Inc(I);  until I >= T;  BIRelease(Context,BIA); 
BIRelease(Context,BIB);  BITrim(BIR);  Result := BIR;end;
The statement "if (OuterPartial > 0) and ((OuterPartial-I) > 0) and
(OuterPartial < N) then" can be rewritten as "if (OuterPartial > 0)
and (OuterPartial > I) and (OuterPartial < N) then". The minimum value
of variable I inside the repeat loop is 0, which makes the presence of
the "(OuterPartial > 0)" condition redundant.
The following patch replaces "if (OuterPartial > 0) and
((OuterPartial-I) > 0) and (OuterPartial < N) then" with "if
(OuterPartial > I) and (OuterPartial < N) then".

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AlexTP · 2024-03-25 13:55

Posted to https://gitlab.com/freepascal.org/fpc/source/-/issues/40710