I am trying to implement FNV hash from http://isthe.com/chongo/tech/comp/fnv/
I converted the PowerBasic's inline asm on that page into 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;
If a size of given file is more that 200KB, the output is random (hash) number. Am I missing something?
Your asm code is somewhat buggy, IMHO. It will crash your application, as it is written.
Correct way to do it could be (not tested, just written here there):
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;
So to read and hash any file, in a pure Delphi way (don't use Windows API like you did):
function fnv32file(const aFileName: TFileName): DWORD;
begin
with TMemoryStream.Create do
try
LoadFromFile(aFileName);
result := fnv32(Memory,Size,0);
finally
Free;
end;
end;
A pure pascal version won't be much slower IMHO (the bottleneck is definitively reading the data from the hard drive):
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;