delphi - FNV的实现

Question

我正在尝试从http://isthe.com/chongo/tech/comp/fnv/实现FNV哈希

我在该页面上将PowerBasic的嵌入式asm转换为Delphi。

    function ReadFileToMem(sPath:string):Pointer;
    var
    hFile:    THandle;
    pBuffer:  Pointer;
    dSize:    DWORD;
    dRead:    DWORD;
    begin
    hFile := CreateFile(PChar(sPath), GENERIC_READ, FILE_SHARE_READ, nil, OPEN_EXISTING, 0, 0);
    if hFile <> 0 then
        dSize := GetFileSize(hFile, nil);
        if dSize <> 0 then
        begin
          SetFilePointer(hFile, 0, nil, FILE_BEGIN);
          GetMem(Result, dSize);
          ReadFile(hFile, Result^, dSize, dRead, nil);
          if dRead = 0 then
            MessageBox(0, PChar('Error reading file.'), PChar('Read Error'), MB_ICONEXCLAMATION)
         end;
        CloseHandle(hFile);
    end;

    function GetPointerSize(lpBuffer: Pointer): Cardinal; // Function by ErazerZ
    begin
      if lpBuffer = nil then
        Result := Cardinal(-1)
      else
        Result := Cardinal(Pointer(Cardinal(lpBuffer) -4)^) and $7FFFFFFC -4;
    end;

     FUNCTION FNV32( dwOffset : Pointer; dwLen : DWORD; offset_basis : DWORD) : DWORD ;
      asm
     mov esi, dwOffset      //;esi = ptr to buffer
     mov ecx, dwLen         //;ecx = length of buffer (counter)
     mov eax, offset_basis  //;set to 2166136261 for FNV-1
     mov edi, 16777619//&h01000193    //;FNV_32_PRIME = 16777619
     xor ebx, ebx           //;ebx = 0
      @nextbyte:
     mul edi                //;eax = eax * FNV_32_PRIME
     mov bl, [esi]          //;bl = byte from esi
     xor eax, ebx           //;al = al xor bl
     inc esi                //;esi = esi + 1 (buffer pos)
     dec ecx                //;ecx = ecx - 1 (counter)
     jnz @nextbyte           //;if ecx is 0, jmp to NextByte
     mov @result, eax      //;else, function = eax

    end;

procedure TForm1.Button1Click(Sender: TObject);
var
pFile : Pointer;
hFile : Cardinal;
begin
//Profiler1['Test'].Start;
pFile := ReadFileToMem(fn);
hFile := FNV32(pFile,GetPointerSize(pFile),2166136261);
//Profiler1['Test'].Stop;
//OutputDebugString(pchar(Profiler1['Test'].AsText[tiAll]));
OutputDebugString(pchar(inttostr(hFile)));
end;

如果给定文件的大小大于200KB，则输出为随机（哈希）数。我想念什么吗？

Answer 1

您的asm代码有些错误，恕我直言。编写时，它会使应用程序崩溃。


您需要预先设置esi / edi / ebx寄存器
参数在eax，ecx，edx寄存器中传递
结果是eax寄存器


正确的方法可以进行测试（未经测试，仅在此处编写）：

function fnv32(dwOffset : Pointer; dwLen : DWORD; offset_basis: DWORD) : DWORD ;
asm // eax=dwOffset ecx=dwLen edx=offset_basis -> result in eax
  push esi
  push edi
  mov esi,eax
  mov eax,edx
  or ecx,ecx
  je @z
  mov edi,16777619
  xor edx,edx
@1:
  mul edi
  mov dl,[esi]
  xor eax,edx
  inc esi
  dec ecx
  jnz @1
@z:
  pop edi
  pop esi
end;

因此，以纯Delphi方式读取和散列任何文件（不要像您一样使用Windows API）：

function fnv32file(const aFileName: TFileName): DWORD;
begin
  with TMemoryStream.Create do
  try
    LoadFromFile(aFileName);
    result := fnv32(Memory,Size,0);
  finally
    Free;
  end;
end;

纯粹的pascal版本不会太慢，恕我直言（瓶颈肯定是从硬盘读取数据）：

function fnv32(dwOffset : PByteArray; dwLen : DWORD; offset_basis: DWORD): DWORD ;
var i: integer;
begin
  result := offset_basis;
  for i := 0 to dwLen-1 do
    result := (result*16777619) xor DWORD(dwOffset^[i]);
end;