C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Even Parity          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message nick.stefanov@gmail.com Guest Posted: Mon Nov 28, 2005 5:38 am    Post subject: Even Parity I am trying to compute an even parity bit for a variable of type char[]. Are there any C++, C# examples on how to first compute the bit and then check it. Thank you very much ahead of time. Nick Back to top roberts.noah@gmail.com Guest Posted: Mon Nov 28, 2005 5:43 am    Post subject: Re: Even Parity nick.stefa... (AT) gmail (DOT) com wrote: Quote: I am trying to compute an even parity bit for a variable of type char[]. Are there any C++, C# examples on how to first compute the bit and then check it. Thank you very much ahead of time. Try the >> operator. Back to top Victor Bazarov Guest Posted: Mon Nov 28, 2005 5:43 am    Post subject: Re: Even Parity [email]nick.stefanov (AT) gmail (DOT) com[/email] wrote: Quote: I am trying to compute an even parity bit for a variable of type char[]. Are there any C++, C# examples on how to first compute the bit and then check it. Thank you very much ahead of time. If there are examples, they would be on the 'Net, don't you think? Have you tried looking for them there? Besides, what does C# have to do with this newsgroup? Back to top Rolf Magnus Guest Posted: Mon Nov 28, 2005 9:45 am    Post subject: Re: Even Parity [email]nick.stefanov (AT) gmail (DOT) com[/email] wrote: Quote: I am trying to compute an even parity bit for a variable of type char[]. Are there any C++, C# examples on how to first compute the bit and then check it. Thank you very much ahead of time. This should give you an idea of how to do it: #include <iostream> #include <limits> int main() { unsigned char x = 0x36; for (int i = 0; i < std::numeric_limits { bool bit = x & (1 << i); std::cout << "bit " << i << " is " << bit << 'n'; } } Back to top n2xssvv g02gfr12930 Guest Posted: Mon Nov 28, 2005 10:26 am    Post subject: Re: Even Parity [email]nick.stefanov (AT) gmail (DOT) com[/email] wrote: Quote: I am trying to compute an even parity bit for a variable of type char[]. Are there any C++, C# examples on how to first compute the bit and then check it. Thank you very much ahead of time. Nick This code will return true if an even parity bit is required bool ParityBit(char inp) { bool Parity = false; for (;inp;inp &= (inp-1)) { Parity ^= true; } return Parity; } Note by setting Parity to true to begin with will result in returning true for odd parity. JB Back to top red floyd Guest Posted: Mon Nov 28, 2005 4:43 pm    Post subject: Re: Even Parity Victor Bazarov wrote: Quote: nick.stefanov (AT) gmail (DOT) com wrote: I am trying to compute an even parity bit for a variable of type char[]. Are there any C++, C# examples on how to first compute the bit and then check it. Thank you very much ahead of time. If there are examples, they would be on the 'Net, don't you think? Have you tried looking for them there? Besides, what does C# have to do with this newsgroup? Actually, it's probably cheapest just to use a lookup table with 256 entries. Back to top Victor Bazarov Guest Posted: Mon Nov 28, 2005 5:38 pm    Post subject: Re: Even Parity red floyd wrote: Quote: Victor Bazarov wrote: [email]nick.stefanov (AT) gmail (DOT) com[/email] wrote: I am trying to compute an even parity bit for a variable of type char[]. Are there any C++, C# examples on how to first compute the bit and then check it. Thank you very much ahead of time. If there are examples, they would be on the 'Net, don't you think? Have you tried looking for them there? Besides, what does C# have to do with this newsgroup? Actually, it's probably cheapest just to use a lookup table with 256 entries. 256 entries in a table for "a variable of type char[]"? How do you figure? V Back to top red floyd Guest Posted: Mon Nov 28, 2005 6:55 pm    Post subject: Re: Even Parity Victor Bazarov wrote: Quote: red floyd wrote: Actually, it's probably cheapest just to use a lookup table with 256 entries. 256 entries in a table for "a variable of type char[]"? How do you figure? V I meant it was faster to use a lookup than to use the shifting methods mentioned above. #include <algorithm> struct parity { unsigned char operator()(unsigned char c) const { static const unsigned char parity_table[] = { // FILL THIS IN }; return parity_table[c]; } }; unsigned char get_parity(unsigned char buf[], int len) { return std::accumulate(buf, buf+len, 0, parity()); } Back to top Victor Bazarov Guest Posted: Mon Nov 28, 2005 7:34 pm    Post subject: Re: Even Parity red floyd wrote: Quote: Victor Bazarov wrote: red floyd wrote: Actually, it's probably cheapest just to use a lookup table with 256 entries. 256 entries in a table for "a variable of type char[]"? How do you figure? V I meant it was faster to use a lookup than to use the shifting methods mentioned above. And I meant to point out that you'd assumed the OP was asking about the unsigned char type, on a system that has CHAR_BITS == 8. The OP did no such thing judging from the post alone. Quote: #include struct parity { unsigned char operator()(unsigned char c) const { static const unsigned char parity_table[] = { // FILL THIS IN How do you "FILL THIS IN"? A bunch of #ifdef's? What if the size of the 'unsigned char' is 16 bits? What if it's 32 bits? Please do not rush to reply. Quote: }; return parity_table[c]; } }; unsigned char get_parity(unsigned char buf[], int len) { return std::accumulate(buf, buf+len, 0, parity()); } V Back to top red floyd Guest Posted: Mon Nov 28, 2005 9:45 pm    Post subject: Re: Even Parity Victor Bazarov wrote: Quote: And I meant to point out that you'd assumed the OP was asking about the unsigned char type, on a system that has CHAR_BITS == 8. The OP did no such thing judging from the post alone. Good point about CHAR_BITS. I stand corrected. However, when generating parity, the size of the data item being paritized(?) is known, and depending on size, a lookup table can definitely be more efficient *and* simpler. Back to top roberts.noah@gmail.com Guest Posted: Tue Nov 29, 2005 4:41 am    Post subject: Re: Even Parity red floyd wrote: Quote: Victor Bazarov wrote: And I meant to point out that you'd assumed the OP was asking about the unsigned char type, on a system that has CHAR_BITS == 8. The OP did no such thing judging from the post alone. Good point about CHAR_BITS. I stand corrected. However, when generating parity, the size of the data item being paritized(?) is known, and depending on size, a lookup table can definitely be more efficient *and* simpler. A combination of both is even better in many cases. For example, you have a 63 bit data item you want to do a parity or a parity check on. 2^63 is big, 2^8 is not overly so. So, bit shift by 8 and do a lookup. Tally the results... Rather similar to the "first bit" algorithm often used in bitboard chess programs. Back to top nick.stefanov@gmail.com Guest Posted: Tue Nov 29, 2005 4:42 pm    Post subject: Re: Even Parity Thank you very much for all of your input. Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         C++Talk.NET Forum Index -> C++ language (comp.lang.c++) All times are GMT Page 1 of 1   Jump to: Select a forum C/C++----------------C LanguageC Language (Moderated)C++ Language (Moderated)C++ language (comp.lang.c++)C++ language, library and standards Non-English C/C++ Newsgroups----------------C++ (German)C++ (French)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.