对比两个文件是否相同的函数

function CompFile(const f1,f2: string): Boolean;
var
  ms1,ms2: TMemoryStream;
  i,p: Integer;
  b1,b2: Byte;
begin
  Result := False;
  if not (FileExists(f1) and FileExists(f2)) then Exit;

  ms1 := TMemoryStream.Create;
  ms2 := TMemoryStream.Create;

  ms1.LoadFromFile(f1);
  ms2.LoadFromFile(f2);

  if ms1.Size <> ms2.Size then
  begin
    ms1.Free;
    ms2.Free;
    Exit;
  end;

  Result := True;
  Randomize;
  for i := 0 to 9 do
  begin
    p := Random(ms1.Size);
    ms1.Position := p;
    ms2.Position := p;
    ms1.ReadBuffer(b1,1);
    ms2.ReadBuffer(b2,1);
    if b1 <> b2 then
    begin
      Result := False;
      Break;
    end;
  end;

  ms1.Free;
  ms2.Free;
end;

根据 "峪飞鹰" 的指点, 略作修改; 不过暂不用 CompareMem 对比所有内存了, 10 次抽样可能会更快一点.

---

function CompFile(const f1,f2: string): Boolean;
var
  fs1,fs2: TFileStream;
  ms: TMemoryStream;
  i,p: Integer;
  b1,b2: Byte;
begin
  Result := False;
  if not (FileExists(f1) and FileExists(f2)) then Exit;
  fs1 := TFileStream.Create(f1, fmOpenRead);
  fs2 := TFileStream.Create(f2, fmOpenRead);

  if fs1.Size <> fs2.Size then
  begin
    fs1.Free;
    fs2.Free;
    Exit;
  end;

  Result := True;
  Randomize;
  for i := 0 to 9 do
  begin
    p := Random(fs1.Size);
    fs1.Position := p;
    fs2.Position := p;
    fs1.ReadBuffer(b1,1);
    fs2.ReadBuffer(b2,1);
    if b1 <> b2 then
    begin
      Result := False;
      Break;
    end;
  end;

  fs1.Free;
  fs2.Free;
end;