SO#13997397

program PointerIteration;

{$APPTYPE CONSOLE}

uses
  System.SysUtils, System.Diagnostics;

function GetHashCode1(Data: PByte; Length: Integer): Integer;
var
  i: Integer;
begin
  Result := 17;
  for i := 1 to Length do
  begin
    Result := Result*23 + Data^;
    inc(Data);
  end;
end;

function GetHashCode2(Data: PByte; Length: Integer): Integer;
var
  EndOfMemoryBlock: PByte;
begin
  EndOfMemoryBlock := PByte(NativeInt(Data)+Length);
  Result := 17;
  while Data<EndOfMemoryBlock do
  begin
    Result := Result*23 + Data^;
    inc(Data);
  end;
end;

function GetHashCode3(Data: PByte; Length: Integer): Integer;
type
  TByteArray = array [0..0] of Byte;
var
  i: Integer;
  ByteArray: ^TByteArray absolute Data;
begin
  Result := 17;
  for i := 0 to Length-1 do
    Result := Result*23 + ByteArray^[i];
end;

var
  i: Integer;
  Data: array of Byte;
  Stopwatch: TStopwatch;

begin
  SetLength(Data, 512*1024*1024);
  for i := 0 to high(Data) do
    Data[i] := i mod 256;

  Stopwatch := TStopwatch.StartNew;
  for i := 1 to 10 do
    GetHashCode1(PByte(Data), Length(Data));
  Writeln(Stopwatch.ElapsedMilliseconds);

  Stopwatch := TStopwatch.StartNew;
  for i := 1 to 10 do
    GetHashCode2(PByte(Data), Length(Data));
  Writeln(Stopwatch.ElapsedMilliseconds);

  Stopwatch := TStopwatch.StartNew;
  for i := 1 to 10 do
    GetHashCode3(PByte(Data), Length(Data));
  Writeln(Stopwatch.ElapsedMilliseconds);

  Readln;
end.