Code Answer: Delphi: How to calculate the SHA hash of a large file

Hi I need to generate a SHA over a 5 Gig file

Do you know of a non string based Delphi library that can do this ?

From stackoverflow

There is a Delphi interface for OpenSSL, isn't there?

That should provide you with better performances.
You should use DCPcrypt v2 and read your file buffered and feed the SHA hasher with the buffer until you've read the complete 5GB file.

If you want to know how to read a large file buffered, see my answer about a file copy using custom buffering.

so in concept (no real delphi code!):
```
function GetShaHash(const AFilename: String)
begin
  sha := TSHAHasher.Create;
  SetLength(Result, sha.Size);
  file := OpenFile(AFilename, GENERIC_READ);
  while not eof file do
  begin
     BytesRead := ReadFile(file, buffer[0], 0, 1024 * 1024);
     sha.Update(buffer[0], BytesRead);
  end;
  sha.Final(Result[0]); 
  CloseFile(file);
end;
```
Davy Landman : I didn't include real Delphi code because I don't have a Delphi compiler installed at the moment.
I would recommend Wolfgang Ehrhardt's CRC/Hash.
http://home.netsurf.de/wolfgang.ehrhardt/

It's fast and "can be compiled with most current Pascal (TP 5/5.5/6, BP 7, VP 2.1, FPC 1.0/2.0/2.2) and Delphi versions (tested with V1 up to V7/9/10)".

I've used it with D11/D12 too.

Davy Landman : yeah, that's a nice one too, very nice asm optimalizations :)
If I remember correctly, Indy comes with several a stream based hash methods.

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