wow...
what a crap i'm writing when even a secretary cannot make a coffe :)
~d
On Tuesday 15 July 2003 16:10, Dmitry wrote:
> The listing provided (math.lst) does not indicate any bugs.
> The code performs ( as I can see) properly.
>
>
> jl performs a jump upon compare on signed numbers.
> So,if
> (char)temp1
> less than zero then it jumps. Starus register in your case being updated
> upon add.b #0x30, &temp1
>
> Appropriate jump insn is:
> ; (jump_insn 13 12 24 (set (pc)
> ; (if_then_else (lt:QI (mem:QI (symbol_ref:HI ("temp1")))
> ; (const_int 0 [0x0]))
> ; (label_ref 22)
> ; (pc))) 7 {*cbranchqi}
>
>
> BTW, In your example V bit cannot be set.
> cheers,
> ~d
>
> On Tuesday 15 July 2003 03:51, Takahashi, Chris wrote:
> > I have discovered code which optimizes improperly. Attached are multiple
> > versions of the code. The code is incorrect if any level of optimization
> > is on (-O1 -O2 -O3 or -Os). test.c is compileable under gcc and
> > msp430-gcc. When targeted at i386 the source generates valid code with
> > both -D_WORK_ (the _WORK_ define switches from a valid to invalid version
> > when compiled) and with out (in fact it creates the same code). Also
> > attached is math.c which contains the problematic code with minimal
> > support code so that a minimal object can be created. math.c also is the
> > same as the preprocessed code of math.c.
> >
> > When compiled for the MSP target it uses msp430 simulator to assess the
> > validity of the code. When the dysfunctional code is compiled it creates
> > a jl instruction in place of a jn instruction after the if statement (see
> > attached math.lst).
> >
> > I have included a make file to make viewing the bug easier. All you need
> > is the simulator in your path and it will make the code and run the test
> > cases.
> >
> > About the code:
> > The attached code (in math.c) increments the upper nibble of temp1 by 3
> > then
> >
> > examines the upper nibble of temp1 to see if it is >= 8. If it is then
> > do nothing, otherwise
> > undo the increment by decrementing the upper nibble by 3.
> >
> > The assembly generated performs the inc by 3 then checks the n and v
> > flags with the jl instruction to determine when to jump. because only
> > the last bit is being checked it is only appropriate to check the n flag
> > -- as the result of the last arithmetic instr is inconsequential (aside
> > from the content of bit 7).
> >
> > If any more info is needed please mail me or the list. And I'll send it
> > ASAP.
> >
> > -Chris Takahashi
--
/*****************************************************************
("`-''-/").___..--''"`-._ (\ Dimmy the Wild UA1ACZ
`6_ 6 ) `-. ( ).`-.__.`) State Polytechnical Univ.
(_Y_.)' ._ ) `._ `. ``-..-' Radio-Physics Departament
_..`--'_..-_/ /--'_.' ,' Saint Petersburg, Russia
(il),-'' (li),' ((!.-' +7 (812) 5403923, 5585314
*****************************************************************/
