Hi Rob The compiler is complaining about the const Zeros declaration Zeros: array[0..1023] of Byte = [0];
Incompatible types: 'Array' and 'Set'. Should it perhaps need to be a global variable which I fill using FillChar? Regards, Ross. ----- Original Message ----- From: "Rob Kennedy" <[EMAIL PROTECTED]> To: "Borland's Delphi Discussion List" <[email protected]> Sent: Friday, November 04, 2005 6:08 AM Subject: Re: Test memory block Ross Levis wrote: > I'm looking for the fastest way to test if a block of memory is all > zeros or not. This needs to be as fast as possible since it is being > tested many times a second. You can use the CompareMem function to compare large blocks of memory at once. It will usually compare at least four bytes at a time instead of comparing each byte separately. Just have a static buffer of all zeros and compare your given buffer to that one. For example: const Zeros: array[0..1023] of Byte = [0]; function IsZero(const Buffer: Pointer; const BufferSize: Cardinal): Boolean; // Returns True if the buffer is all-bits-zero. Returns False if // the buffer contains non-zero bytes, or if its length is zero. var BytesRemaining: Cardinal; ZeroBytes: Cardinal; Buf: PByte; begin Result := False; Buf := Buffer; ZeroBytes := SizeOf(Zeros); BytesRemaining := BufferSize; while BytesRemaining >= ZeroBytes do begin if not CompareMem(@Zeros, Buf, ZeroBytes) then exit; Dec(BytesRemaining, ZeroBytes); Inc(Buf, ZeroBytes); end; if BytesRemaining > 0 then Result := CompareMem(@Zeros, Buf, BytesRemaining); end; This function should work more efficiently the larger you make Zeros. You can also make CompareMem faster by using an implementation from the Fastcode Project. http://fastcode.sourceforge.net/fastcodeproject/60.htm Download form here: http://fastcode.sourceforge.net/fastcodeproject/55.htm -- Rob _______________________________________________ Delphi mailing list -> [email protected] http://www.elists.org/mailman/listinfo/delphi
