Re: [fpc-pascal] When are used units recompiled? (wiki page added)
On Sun, Apr 09, 2006 at 10:58:09PM +0200, Giovanni Premuda wrote: > Tom Verhoeff ha scritto: > >This makes it much less attractive to release units without source > >code. That may be understandable from an open-source perspective, > >but in teaching I find it useful or even necessary to provide units > >without source code. > > > IN TEACHING? Why this shouting and bafflement? Here are two reasons: * In order to teach students to use services (=units) solely based on the contract (= specification), we withhold the implementation and only provide the compiled unit. That way the implementation cannot be consulted (=abused). * In some cases, the unit incorporates some "secrets", e.g. related to grading. Consider e.g. an assignment where one has to develop an algorithm for finding the median of an odd number of distinct integers by using only a binary comparison operator. To enforce the use of only binary comparisons, we don't give them the set directly, but rather give them a unit, which "hides" the actual integers and provides the comparison operator. Of course, this hidden set can be made inaccessible from the outside by putting it in the implementation part. In that case, it might seem harmless to give away the source code. However, there are more complications: e.g. where does the actual set come from? It is not built into the unit, but read from a file, or generated via a random generator with a seed read from a file. The data in the file is scrambled so that the students cannot simply read it and abuse that information. Unless you want to use sophisticated encryption techniques, it is easier to use a "proprietary" method and not give them the source code. In fact, the unit need not have a set of numbers to start with, but could construct a "worst case" scenario base on the actual sequence of operations carried out by the program (a so-called adversary). We don't want to give away the strategy of the adversary algorithm. > Btw. no sane commercial Delphi developer has ever considered using a > component without source code at least since Delphi 2.0. Look at the > offering of component vendors and you will see that they invariably > offer source code licenses. Most likely because the 'compatibility mechanism' is not very effective. Compatibility is one of the big problems in component-based development. Tom -- E-MAIL: T.Verhoeff @ TUE.NL | Fac. of Math. & Computing Science PHONE: +31 40 247 41 25| Eindhoven University of Technology FAX:+31 40 247 54 04| PO Box 513, NL-5600 MB Eindhoven http://www.win.tue.nl/~wstomv/ | The Netherlands ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] When are used units recompiled? (wiki page added)
> On Sun, Apr 09, 2006 at 10:58:09PM +0200, Giovanni Premuda wrote: > > Btw. no sane commercial Delphi developer has ever considered using a > > component without source code at least since Delphi 2.0. Look at the > > offering of component vendors and you will see that they invariably > > offer source code licenses. > > Most likely because the 'compatibility mechanism' is not very effective. No, also to be able to maintain the component (fix bugs and look at the implementation). Both the companies I did Delphi work for professionaly, mandated full source for the components. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] When are used units recompiled? (wiki page added)
On Mon, 10 Apr 2006, Marco van de Voort wrote: On Sun, Apr 09, 2006 at 10:58:09PM +0200, Giovanni Premuda wrote: Btw. no sane commercial Delphi developer has ever considered using a component without source code at least since Delphi 2.0. Look at the offering of component vendors and you will see that they invariably offer source code licenses. Most likely because the 'compatibility mechanism' is not very effective. No, also to be able to maintain the component (fix bugs and look at the implementation). Both the companies I did Delphi work for professionaly, mandated full source for the components. I would never buy or use components without sources. All components I ever bought/downloaded contained bugs, without exception, and we can't wait for the company to fix them. Michael. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
[fpc-pascal] real numbers infinity
Hello list, when a real number overflows the program halts with EInvalidOp error. How can I make the program behave the more standard way, where the variable gets the value "inf" and execution continues normally? This is vital for many tasks, like fractal computation. example program: $ cat realover.pas program realover; Uses variants; var r:real; BEGIN r:=2; while True do begin r:=r**2; writeLn(r); end; END. current output: $ ./realover 4.000E+000 1.600E+001 2.560E+002 6.5536000E+004 4.29496729600E+009 1.844674407370955E+019 3.402823669209385E+038 1.157920892373162E+077 1.340780792994260E+154 An unhandled exception occurred at $0805F1C6 : EInvalidOp : Invalid floating point operation $0805F1C6 $0805F895 $08053CDF $08048182 desired output: 4.000E+000 1.600E+001 2.560E+002 6.5536000E+004 4.29496729600E+009 1.844674407370955E+019 3.402823669209385E+038 1.157920892373162E+077 1.340780792994260E+154 inf inf inf ... Thanks in advance, Dimitris P.S. Why when the program doesn't include the variants unit the program complains at runtime? What is that unit? ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] real numbers infinity
Dimitris, > when a real number overflows the program halts with EInvalidOp error. > How can I make the program behave the more standard way, where the > variable gets the value "inf" and execution continues normally? This is > vital for many tasks, like fractal computation. You can use try..except..end block and switch -Sd when compile: program realover; Uses math; var r:real; BEGIN r:=2; while True do begin try r:=r**2; writeLn(r); except r:=infinity; writeLn(r); // break end; end; END. Or you may take a look IEEE specification if it is necessary to create your own big float support for larger precision with fractals. > P.S. Why when the program doesn't include the variants unit the program > complains at runtime? What is that unit? At windows, it is not necessary for this example. Variants unit provide new type definition and supported functions, which can consist any simple type (integer, string, etc). Sasa ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Internal linker status
> No. 2.0.2 is a release and it sources won't change. If the fix proves > it's stability in 2.1.1, it will be merged back to 2.0.3 which will be > the base for the next release: 2.0.4. Yes, that would be necessary. A fix for 4922 is essencial. > We used the GNU linker on win32 for years and it worked. We know that it > has it's flaws but it isn't that bad after all. On Windows platform with small ammount of phisical memory (<=128MB), compiling is very inconveniente and slow. New internal linker should solve that problem as well (as mentioned already). Sasa ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
