Improvement of BIRegularMultiply

from 'lagprogramming'.

packages/fcl-hash/src/fptlsbigint.pas has

    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".

patch.diff