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Author	Topic: BIT Question Part 2 - PB Compiler output
Lothar Pink Member	posted March 03, 2004 08:24 AM If I compile & run the following code: FUNCTION PBMAIN AS LONG DIM a AS INTEGER ! nop ! nop BIT SET a, 6 ! nop ! nop ! mov eax, 0 ! mov [eax], eax ; I always use that in order to trigger a GPF so I can view the disassembly END FUNCTION It compiles to 004010A3 nop 004010A4 nop 004010A5 mov eax,6 004010AA lea ebx,[ebp-80h] 004010AD mov dword ptr [ebp-80h],esi 004010B0 call 004017B3 004010B5 mov esi,dword ptr [ebp-80h] 004010B8 nop 004010B9 nop 004010BA mov eax,0 004010BF mov dword ptr [eax],eax At 004017B3: 004017B3 call 004017CB 004017B8 or byte ptr [ebx],al 004017BA ret At 004017CB: 004017CB mov cl,al 004017CD shr eax,3 004017D0 add ebx,eax 004017D2 and cl,7 004017D5 mov al,1 004017D7 shl al,cl 004017D9 ret Why not just use "bts" ? I don't want to complain about the performance but what's wrong with bts? Best Regards ------------------ ADDED: With REGISTER NONE - similar 004010A3 nop 004010A4 nop 004010A5 mov eax,6 004010AA lea ebx,[ebp-80h] 004010AD call 004017B3 004010B2 nop 004010B3 nop 004010B4 mov eax,0 004010B9 mov dword ptr [eax],eax [This message has been edited by Lothar Pink (edited March 03, 2004).] IP: Logged
Michael Mattias Member	posted March 03, 2004 08:29 AM BIT SET a, 6 Why not 'bts'?, well, Why not.. a = a OR 64% I do not know what 'bts' does, but maybe it has something to do with the fact that the BIT SET function will set bits beyond the nominal range of the operand? Or maybe 'bts' requires a certain minimum processor type? [This message has been edited by Michael Mattias (edited March 03, 2004).] IP: Logged
Lothar Pink Member	posted March 03, 2004 08:31 AM I don't know about the processor compatibility, but BTS - as far as I know - allows to set a bit at ANY position in memory, as long as it's in the process memory. So, it's a single statement - instead of two CALLs here. PS: The reason I'm asking is actually if there is some reason why I should NOT use the BTS assembler instruction - since PB is avoiding it. ------------------ [This message has been edited by Lothar Pink (edited March 03, 2004).] IP: Logged
Paul Dixon Member	posted March 03, 2004 12:00 PM Lothar, <<! mov [eax], eax ; I always use that in order to trigger a GPF so I can view the disassembly>> That's what "!int 3" is for. It calls the current debugger. The Bit set ASM opcodes have existed since the 386 so I don't see why they aren't used. They can set any bit but only 2^32 BITS are addressable within a single instruction (i.e.1/8th of the total RAM that is addressable). Paul. IP: Logged
Marco Pontello Member	posted March 03, 2004 04:47 PM See this for a quick way to look at the compiler output for some lines of PowerBASIC code: http://www.powerbasic.com/support/forums/Forum7/HTML/002258.html Bye! ------------------ Try TrID file identifier! Over 990 filetypes and counting... ;) Give a powerfull scriptable Lua interface to your application with PowerBLua IP: Logged

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