----- Original Message ----- From: "John Dammeyer" <[EMAIL PROTECTED]> To: "'Borland's Delphi Discussion List'" <[email protected]> Sent: Saturday, November 05, 2005 3:59 PM Subject: RE: Test memory block
Hi Ross, You're making a lot of assumptions on how the compiler is going to do things. Although this is usually more applicable to embedded micro's I can't stress enough if speed or size is a concern you must look at how the compiler does things. Your method does 'appear' tidier but has some speed penalties. The biggest one is Buffer32[i] You may recall I took specific pains to declare and use pointers here since ultimately that's what the compiler does when it dereferences Buffer32[i]. Since 'i' is a loop variable Delphi complains if you assign to it so a peephole optimizer may just discover the code sequence and substitute pointer arithmetic but can you be sure. Since the goal is speed, it's not a good idea to include an extra addition and multiplication @Buffer32 + i * sizeof(longword) which is what Buffer32[i] is. The second part of your test looks at the last 3 bytes of a longword. First, I believe it checks up to the first 3 bytes of the buffer which you've already looked at. Minor glitch. Unless you're expecting the array to sit on a BYTE boundry rather than long word. Again, checking the compiler you'll see that it always declares data on at least a 16 bit boundry. It's not efficient for the compiler to use odd addresses. That showed up in the original PASCAL definition with the word Packed. John Dammeyer Wireless CAN with the CANRF module now available. http://www.autoartisans.com/products Automation Artisans Inc. Ph. 1 250 544 4950 > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Ross Levis > Sent: Friday, November 04, 2005 3:10 PM > To: Borland's Delphi Discussion List > Subject: Re: Test memory block > > > Just as a matter of interest, I came up with my own fast > method working > along the lines of John's method but I think this is tidier. > > type > TBuffer32 = array[0..0] of LongWord; > PBuffer32 = ^TBuffer32; > > TBuffer8 = array[0..0] of Byte; > PBuffer8 = ^TBuffer8; > > function IsZero(Buffer32: Pointer; BufferSize: Integer): Boolean; > var > Size32: Integer; > Buffer8: PBuffer8; > Buffer32: PBuffer32; > i: Integer; > begin > Result := False; > Buffer32 := Buffer; > Size32 := BufferSize shr 2; > for i := 0 to Size32-1 do > if Buffer32[i] <> 0 then // test 4 bytes at a time > Exit; > Buffer8 := Buffer; > for i := 0 to BufferSize - (Size32 shl 2) -1 do > if Buffer8[i] <> 0 then // test remaining 1,2, or 3 bytes > Exit; > Result := True; > end; > > > Regards, > Ross. > > _______________________________________________ > Delphi mailing list -> [email protected] > http://www.elists.org/mailman/listinfo/delphi > > _______________________________________________ Delphi mailing list -> [email protected] http://www.elists.org/mailman/listinfo/delphi _______________________________________________ Delphi mailing list -> [email protected] http://www.elists.org/mailman/listinfo/delphi
