on goto
in [ASM]
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From: io_x on 7 May 2010 04:18 "Juha Nieminen" <nospam(a)thanks.invalid> ha scritto nel messaggio news:4be2f44f$0$11839$7b1e8fa0(a)news.nbl.fi... > In comp.lang.c++ Nathan <nathancbaker(a)gmail.com> wrote: >> On Apr 28, 1:16 am, Juha Nieminen <nos...(a)thanks.invalid> wrote: >>> Value_t* MyClass::findValue(const Value_t& value) >>> { >>> for(size_t xInd = 0; xInd < data.size(); ++xInd) pheraps i don't understand C or C++; are you sure that "data.size()" return the max index of x? in how i read it, it could return the number of NxNxN table elements or the size in bytes of data object than where "data" came from: is it global? >>> for(size_t yInd = 0; yInd < data[xInd].size(); ++yInd) >>> for(size_t zInd = 0; zInd < data[xInd][yInd].size(); ++zInd) >>> { >>> if(data[xInd][yInd][zInd] == value) >>> return &data[xInd][yInd][zInd]; >>> } >>> >>> return 0; >>> } could be this ok for a mXmXm matrix that has the index in the same range 0..m? Value_t* MyClass::findValue(Value_t& value) {size_t x, y, z, m; m=sizeof(data)/sizeof(data[0][0][0]); m=sqrt3(m); // 3 radix for(x=0; x <m; ++x ) for(y=0; y<m; ++y) for(z=0; z<m; ++z) if(data[x][y][z]==value) return &data[x][y][z]; return 0; } >> Hi Juha, >> >> I think that you either copied this from a poorly-written beginner C++ >> book or you failed to understand what the author was attempting to >> demonstrate with that kind of code and that you did not 'catch on' >> that it is not (in any way) demonstrative of how one walks a series of >> sequential cells in the real world. > > I don't know if you are being sarcastic, patronizing, or honestly don't > know what you are talking about, but I'll let it pass. in the code you write, for me nothing is clear it is not question if "is it easy?", it is question "is it right?" >> Why do you insist on writing control structures that serve little >> actual purpose? For instance, it should be obvious that you only >> require ONE loop and a few conditionals to achieve your desired (or >> assumed) goal. E.G... >> >> ,--- >> result = value >> xInd = 0 >> yInd = 0 >> zInd = 0 >> while ( data[xInd][yInd][zInd] != value && result != 0) >> { >> ++zInd; >> if (( zInd < data[xInd][yInd].size() ) != true ) { zInd = 0; + >> +yInd}; >> if (( yInd < data[xInd].size() ) != true ) { yInd = 0; ++xInd}; >> if (( xInd < data.size() ) != true ) { result = 0 }; >> } >> return result >> `--- > > The goal was to make the function simpler, not more complicated. > Your version (even if it's fixed to actually do the same thing, and even > after removing the superfluous conditionals) is significantly more > complicated for many reasons. Most importantly, it uses a strange idiom > which the vast majority of programmers are not familiar with and don't > use (and why would they?) It takes significantly more time to understand > what your code is doing, as well as to verify that it's doing it correctly. > My original version with three nested loops is a lot easier to understand, > and a lot easier to verify that it works correctly. > > And what for? It's not more efficient, shorter or does it do anything > that the original wouldn't do. Moreover, it's very possible that in some > similar circumstances a compile could be able to perform better optimizations > on the original nested loop version than yours (eg. by applying loop > unrolling and other optimization techniques). > >> Of course, this is a rather useless (maybe even retarded) function to >> begin with, because it only tells you IF the 'value' is located >> "somewhere" within that array -- it gives you absolutely no indication >> of "where" in that array you might be able to access the item which >> matches your search criteria. > > Actually the function returns a pointer to the found element, or null > if the element is not found.
From: Nick Keighley on 7 May 2010 04:17 On 6 May, 08:50, Keith Thompson <ks...(a)mib.org> wrote: > The original problem is to traverse a 3-dimensional array. A triple > nested loop is the most obvious way to do that. There might be > some advantages in converting it to a single loop, but clarity > isn't one of them, at least in this case. I considered submitting a single loop solution as a joke. It never crossed my mind someone would seriusly propose it!
From: Juha Nieminen on 7 May 2010 06:34 In comp.lang.c++ io_x <a(a)b.c.invalid> wrote: > pheraps i don't understand C or C++; > are you sure that "data.size()" return the max index of x? Standard C++ data containers use the size() member function to tell the amount of elements. > than where "data" came from: is it global? Does it matter? Anyways, since this was clearly a member function implementation, it's safe to assume that 'data' is a member variable (well, I could have used an even better name, such as 'mData', but as I said, it doesn't really matter). > could be this ok for a mXmXm matrix that has the index in the > same range 0..m? > > Value_t* MyClass::findValue(Value_t& value) > {size_t x, y, z, m; > m=sizeof(data)/sizeof(data[0][0][0]); > m=sqrt3(m); // 3 radix > for(x=0; x <m; ++x ) > for(y=0; y<m; ++y) > for(z=0; z<m; ++z) > if(data[x][y][z]==value) > return &data[x][y][z]; > return 0; > } What the function is doing isn't important. The point is how to exit the nested loops most cleanly. > in the code you write, for me nothing is clear > it is not question if "is it easy?", it is question "is it right?" Well, knowing the language is helpful.
From: Daniel T. on 7 May 2010 10:16 Nick Keighley <nick_keighley_nospam(a)hotmail.com> wrote: > On 6 May, 08:50, Keith Thompson <ks...(a)mib.org> wrote: > > > The original problem is to traverse a 3-dimensional array. �A triple > > nested loop is the most obvious way to do that. �There might be > > some advantages in converting it to a single loop, but clarity > > isn't one of them, at least in this case. > > I considered submitting a single loop solution as a joke. It never > crossed my mind someone would seriusly propose it! I seriously proposed it. I think it is the best solution for the job (not your code specifically of course, but the idea of a single loop traversing a single container.)
From: Keith Thompson on 7 May 2010 11:56
"Daniel T." <daniel_t(a)earthlink.net> writes: > Nick Keighley <nick_keighley_nospam(a)hotmail.com> wrote: >> On 6 May, 08:50, Keith Thompson <ks...(a)mib.org> wrote: >> >> > The original problem is to traverse a 3-dimensional array. A triple >> > nested loop is the most obvious way to do that. There might be >> > some advantages in converting it to a single loop, but clarity >> > isn't one of them, at least in this case. >> >> I considered submitting a single loop solution as a joke. It never >> crossed my mind someone would seriusly propose it! > > I seriously proposed it. I think it is the best solution for the job > (not your code specifically of course, but the idea of a single loop > traversing a single container.) Can a container contain another container, which in turn contains another container? If so, isn't a nested loop the most natural way to traverse the elements? -- Keith Thompson (The_Other_Keith) kst-u(a)mib.org <http://www.ghoti.net/~kst> Nokia "We must do something. This is something. Therefore, we must do this." -- Antony Jay and Jonathan Lynn, "Yes Minister" |