- Reverse Iteration Fractal Encryption... - 1 Update
- enum with flags, overloaded operators and switch - 2 Updates
- list of operating systems that can run C++? - 3 Updates
| Peter Fairbrother <peter@tsto.co.uk>: Jun 26 04:52PM +0100 On 21/02/16 21:38, Chris M. Thomasson wrote: > choose a point in the n'th level set. The point can be chosen > by taking a starting point just outside the circle delimiting > the target set, I don't get this bit. I am not a chaos theorist, and I do not understand _exactly_ what is being proposed. Could you explain further? Please try and be as precise as you can. For example, what is the n-th level set? Is it the same thing as the target set? (if so, please don't call it by two different names... ) I initially thought it was the set of points which remain less than some value after n iterations (presumably of x -> x^2 + c) - or possibly that set minus the set for n-1 iterations - but I don't see how that would be delimited by a circle. Can c be freely chosen from some large range? > and applying inverse iteration, choosing roots > by sign according to the bits in the sequence to be encoded. Is that the actual encryption operation? > until the point lands in the target set. The decoded message > would have n bits determined by writing down the sign of the > imaginary component of the escape orbit for each iteration. This last part 5, decode by repeatedly iterating and taking the sign of the imaginary parts as plaintext bits, seems like it would work. but oh oh, what is an escape orbit? for each iteration? If you/he means the imaginary part of x, then it seems to make some sense. But what is the imaginary component of the escape orbit of an iteration? I still don't see how you get the initial ciphertext. Repeated reverse iterations and choosing which root to use, OK, I get that. But how do you choose the starting point, given some arbitrarily-chosen c? Assuming you can do that, as a cipher it seems to have several disadvantages: first, it is computationally expensive. Second, the ciphertext is somewhat longer than the plaintext. For cipher purposes, you need too be able to encrypt say 128 bits in a block - there are some 64-bit block ciphers still around, but they are deprecated, and some people say you need 256 bits in a block nowadays. As a corollary to the above, the actual length needed for the ciphertext is ... variable, which is a bit disconcerting. Another corollary, you might have to check whether each block decrypts correctly, so as to tell whether you have enough precision .. So in general it isn't that useful as a cipher. except .. it *may* have a slightly interesting security property, ie a strong proof of security. This is kinda a holy grail for some cryptologists, and if I am right about that, it may have some limited use. > Sounds easy right? Maybe if you are a chaos theorist .. - Peter Fairbrother ps ignore anything austinobyrne has to say - he is a well-known idiot. > the fractal dimension of the Julia set, and the degree of > imbalance of the contractivity in the tree traversal of the > Julia set." ps nope, that makes no sense to me either .. |
| Marcel Mueller <news.5.maazl@spamgourmet.org>: Jun 26 04:31PM +0200 When I use enums with flags an define the type safe bit operators I get warning in switch statements when I have bit combinations in a case constant. (case value not in enumerated type) Basically the overloaded operators cause the argument to switch to be of the enum type rather than int. And now the compiler (here gcc) does some consistency checks. It is just a warning and I can turn it off, but this disables another sometimes useful warning for other enum types that not all enum values of the switch are handled. Is there anything else I can do except for casting to int at the switch statement? enum Flags { None = 0 , Val1 = 1 , Val2 = 2 //... }; inline constexpr Flags operator|(Flags l, Flags r) { return (Flags)((int)l|r); } // further operators int main() { Flags f = Val1|Val2; switch (f) {default: return 0; case Val1: return 1; case Val2: return 2; case Val1|Val2: // Warning! return 3; } } |
| "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>: Jun 26 05:19PM +0200 On 26.06.2016 16:31, Marcel Mueller wrote: > When I use enums with flags an define the type safe bit operators I get > warning in switch statements when I have bit combinations in a case > constant. (case value not in enumerated type) [snip] > return 3; > } > } enum Flags { None = 0 , Val1 = 1 , Val2 = 2 //... }; inline constexpr Flags operator|(Flags l, Flags r) { return (Flags)((int)l|r); } // further operators int main() { Flags f = Val1|Val2; switch (+f) {default: return 0; case Val1: return 1; case Val2: return 2; case Val1|Val2: // Warning! return 3; } } Cheers & hth., - Alf |
| "J. Clarke" <j.clarke.873638@gmail.com>: Jun 26 05:10AM -0400 In article <fcdaa56d-59a0-4b61-925c-f31f55a89cf0@googlegroups.com>, ootiib@hot.ee says... > That is so silly. The tongue does not matter. What matters is what is > expressed in it. So better compare what known software is written in > C++ and what is in C#. So what known software was written in C in 1968 and what does that fact tell us about the utility of C? Comparing a new language with an old language on the basis of "what was written in it" seems kind of silly. |
| "J. Clarke" <j.clarke.873638@gmail.com>: Jun 26 05:34AM -0400 In article <nderds$g8i$1@news.xmission.com>, legalize+jeeves@mail.xmission.com says... > >Does there exist a list of operating systems/hardware that I can target > >in C++? > All of them. All of them? Really? So tell us where to get a C++ compiler that targets the Zuse Z4. > >My office mate is arguing with me that C# is now more portable than C++, > >because...mono. He is making me angry. > Every other language sits on top of some layer that is either C or C++. That would be news to Fortran, LISP, ALGOL, COBOL, RPG, APL, Simula, SNOBOL, Speakeasy, BASIC, PL/I, and JOSS, among others. C++ is highly portable and targets a great many systems, but don't overstate the case. |
| "J. Clarke" <j.clarke.873638@gmail.com>: Jun 26 05:49AM -0400 In article <ndi9dc$1raf$2@gioia.aioe.org>, klammerj@NOSPAM.a1.net says... > I mean it's a nice marketing spin and all, but if the goal is > portability (as they claim) but it'll only run on windowze, > something has to be wrong, no? Mono is a subset of dotNet and it doesn't "only run on Windows". You can write C++ code that "only runs on Windows" you know, all you have to do is access system services that are not present on other operating systems. |
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