Thanks David, I couldn't have put it better :-)
As you can infer, I am in a different time zone so your emails tend to come in after I have gone home for the day! Regards Luke -----Original Message----- From: David Brown [mailto:da...@westcontrol.com] Sent: Thursday, 23 January 2003 9:27 PM To: mspgcc-users@lists.sourceforge.net Subject: Re: [Mspgcc-users] Struct assignment BUG... > Dear Garst, > > I can see that there are some friends in the list that had found a bug from > what Oleg has originally posted ( struct declararation and use ). I would > like to respectfully ask this friends what the bug is an which is the > interesting code it generates, so I ( and probably someone else ) could > learn something new. It is clear that I missed something. Can the original > Oleg's code work fine ? Why ? Thanks in advance. > The array v ( struct x *v[2] ) contains two elements, each of which is a pointer to an "x" structure. I think everyone is clear on that one. The original code was: void swap(void) { struct x tmp; tmp=*v[0]; *v[0]=*v[1]; *v[1]=tmp; } And the suggested change was: void swap(void) { struct x *tmp; /* this declaraction should be struct x *tmp , and not the variable tmp of type struct x !!! */ *tmp = *v[0]; *v[0]= *v[1]; *v[1]= *tmp; } In the first case, tmp is declared to be a "struct x". The structure that v[0] points to is copied into tmp. Then the structure that v[1] points to is copied into the space that v[0] points to, and then the tmp structure is copied into the space that v[0] points to. I think you were trying to suggest that the pointers should be swapped, not the structs they pointed to. In that case, the code would have been: struct x *tmp; tmp = v[0]; v[0] = v[1]; v[1] = tmp; Note that there are no longer dereferencers (the *'s). The code you have given will do pretty much the same thing as the original code, except that the temporary area is accessed indirectly through a pointer tmp, which is not initialised. In other words, the code will use a random bit of memory somewhere (which may not physically exist) for the scratch space, which is not what you want. The compiler should give you a warning on that sort of thing (if not, add the -W and -Wall flags to your compiler flags). mvh. David > > > > Will this work? > > > > struct x{ /* struct of type x defined */ > > int a,b,c,d; > > }; > > > > struct x *v[2]; /* array of 2 pointers to structures of type x - > > somewhere initialized, OK ?*/ > > > > /* swap pointers, this means after call to swap(), v[0] holds the > > pointer to v[1] and viceversa */ > > void swap(void) { > > struct x *tmp; /* this declaraction should be struct x *tmp , and > > not the variable tmp of type struct x !!! */ > > *tmp = *v[0]; > > *v[0]= *v[1]; > > *v[1]= *tmp; > > } > > > > Garst > > > > > Luke Hoffmann wrote: > > > > > > Sorry, I'll repost this with HTML off ;-) > > > > > > Hi, > > > > > > I think Oleg has identified a real problem. > > > Lets leave the question of "is this the best way to do it" aside and > realise that "this is the best way to reproduce the problem"! > > > > > > The swap() function is not swapping pointers it is swapping the contents > of structures. > > > This is a valid operation and it produces some interesting code! > > > Clearly the code attached is wrong. > > > > > > Regards > > > Luke > > > > > > > > > -----Original Message----- > > > From: Roberto G. Berner [mailto:booleangene...@ciudad.com.ar] > > > Sent: Thursday, 23 January 2003 4:36 AM > > > To: mspgcc-users@lists.sourceforge.net > > > Subject: RE: [Mspgcc-users] Struct assignment BUG... > > > > > > Dear Oleg: > > > > > > Accept my apologies, but I think you should check this. If I am wrong, > please excuse me. > > > > > > > > > struct x{ /* struct of type x defined */ > > > int a,b,c,d; > > > }; > > > > > > struct x *v[2]; /* array of 2 pointers to structures of type x - > somewhere initialized, OK ?*/ > > > > > > /* swap pointers, this means after call to swap(), v[0] holds the > pointer to v[1] and viceversa */ > > > void swap(void) { > > > struct x tmp; /* this declaraction should be struct x *tmp , and not > the variable tmp of type struct x !!! */ > > > tmp=*v[0]; /* tmp should be a pointer in order to hold pointers > properly */ > > > *v[0]=*v[1]; > > > *v[1]=tmp; > > > } > > > > > > Kind regards, > > > > > > Roberto G. Berner > > > booleangene...@ciudad.com.ar > > > ven...@increible.homelinux.com > > > 4308 3500 tel > > > 4308 3700 fax > > > 15 5122 6095 cel > > > ----- Original Message ----- > > > From: Oleg Skydan > > > To: mspgcc-users@lists.sourceforge.net > > > Sent: Wednesday, January 22, 2003 4:27 PM > > > Subject: Re: [Mspgcc-users] Struct assignment BUG... > > > > > > Dear Roberto, > > > > > > The swap function exchanges the contents of the two structs, > > > pointed by elements of the array v, so there a significant BUG. > > > > > > I have omitted the initialization section for simplicity (I have found > this BUG in > > > a real program, which is very large). > > > > > > Anyway the stack pointer should point to the same location at the > function > > > exit and entry (unless it is explicitly changed, using asm statement for > example). > > > > > > Thanks, > > > Oleg. > > > ----- Original Message ----- > > > From: Roberto G. Berner > > > To: mspgcc-users@lists.sourceforge.net > > > Sent: Wednesday, January 22, 2003 6:25 PM > > > Subject: RE: [Mspgcc-users] Struct assignment BUG... > > > > > > Dear Oleg: > > > > > > I think that there is no bug. Should I suggest trying ... > > > > > > struct x *tmp; > > > > > > Kind regards, > > > > > > Roberto G. Berner > > > booleangene...@ciudad.com.ar > > > ven...@increible.homelinux.com > > > 4308 3500 tel > > > 4308 3700 fax > > > 15 5122 6095 cel > > > ----- Original Message ----- > > > From: Oleg Skydan > > > To: MSP430 GCC > > > Sent: Wednesday, January 22, 2003 12:12 PM > > > Subject: [Mspgcc-users] Struct assignment BUG... > > > > > > Hello, All ! > > > > > > I found a significant BUG when using struct assignment. > > > > > > Here is the sample: > > > > > > struct x{ > > > int a,b,c,d; > > > }; > > > > > > struct x *v[2]; > > > > > > void swap(void) > > > { > > > struct x tmp; > > > tmp=*v[0]; > > > *v[0]=*v[1]; > > > *v[1]=tmp; > > > } > > > > > > And here is GCC's listing (with -O option): > > > > > > /*********************** > > > * Function `swap' > > > ***********************/ > > > swap: > > > /* prologue: frame size = 8 */ > > > .L__FrameSize_swap=0x8 > > > .L__FrameOffset_swap=0x8 > > > sub #8, r1 ; 8, fpn 0 > > > /* prologue end (size=1) */ > > > mov &v, r15 > > > mov @r15+, @r1 > > > mov @r15+, 2(r1) > > > mov @r15+, 4(r1) > > > mov @r15+, 6(r1) > > > mov &v+2, r14 > > > mov @r14+, 0(r15) > > > mov @r14+, 2(r15) > > > mov @r14+, 4(r15) > > > mov @r14+, 6(r15) > > > mov &v+2, r15 > > > mov @r1+, 0(r15) ;We should not change the stack pointer here ! > > > mov @r1+, 2(r15) > > > mov @r1+, 4(r15) > > > mov @r1+, 6(r15) > > > /* epilogue: frame size=8 */ > > > add #8, r1 ;After this command the stack pointer > points to the illegal location ! > > > ret > > > /* epilogue end (size=2) */ > > > /* function swap size 33 (30) */ > > > > > > I use win32 version (from 10.12.2002). > > > Thanks, Oleg. > > > > > > > > > > > > > > > ------------------------------------------------------- > > This SF.net email is sponsored by: Scholarships for Techies! > > Can't afford IT training? All 2003 ictp students receive scholarships. > > Get hands-on training in Microsoft, Cisco, Sun, Linux/UNIX, and more. > > www.ictp.com/training/sourceforge.asp > > _______________________________________________ > > Mspgcc-users mailing list > > Mspgcc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/mspgcc-users > > > > > > > > ------------------------------------------------------- > This SF.NET email is sponsored by: > SourceForge Enterprise Edition + IBM + LinuxWorld = Something 2 See! > http://www.vasoftware.com > _______________________________________________ > Mspgcc-users mailing list > Mspgcc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/mspgcc-users > > ------------------------------------------------------- This SF.NET email is sponsored by: SourceForge Enterprise Edition + IBM + LinuxWorld = Something 2 See! http://www.vasoftware.com _______________________________________________ Mspgcc-users mailing list Mspgcc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mspgcc-users ____ This communication contains information which is confidential and the copyright of Nautronix. 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