Re: [fpc-devel] Different results of random(int32) and random(int64) for negative limit value
On 24/05/17 09:35, Thaddy de Koning wrote: The implementation is _*not *_undefined for negative values,_unless you say that you define it as undefined_. That is exactly what "undefined" means: the implementation was not designed to handle such values, so whatever you get as a result is undefined. Jonas ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
Re: [fpc-devel] Different results of random(int32) and random(int64) for negative limit value
Jonas, sorry for the late response: The implementation is _*not *_undefined for negative values,_unless you say that you define it as undefined_. Because you seem to have implemented it or most of it. It renders a mathematical comparable distribution in the negative to the positive values. In both Turbo Pascal as in Delphi and because they use a different algorithm and made an implementation error as well, the negative values are indeed not defined. But that's because of the algorithm and because of the implementation by Borland (yes, it stems from Borland times). The Mersenne Twister we use is also valid for negative values and if you want I can send you the mathematical proof. I already made the LCG in Delphi compatible mode available on the wiki and that implementation differs in so far as that it corrects the "undefined for negative values" for that algorithm too. It is 100% compatible for the Delphi documented range, btw. I am busy evaluating important Random implementions for different languages, so an FPC library is available for data that is generated in a different language and relies on a particular PRNG. Also note that the output of the current random is strictly valid for 32 bit only. In my code I already added a 64 bit version. Regards, Thaddy On 5/20/2017 2:57 PM, Jonas Maebe wrote: On 20/05/17 14:36, Martin Schreiber wrote: Is this intended? If not, which one is correct? random(x) is undefined for negative parameters. It should have had an unsigned parameter, like in Turbo Pascal (where it is word). Delphi defines it as always returning a positive value, but I don't know what happens if you pass a negative parameter there. Jonas ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
Re: [fpc-devel] Different results of random(int32) and random(int64) for negative limit value
Of course 64 and 32 bit are the sizes, not the platform! That may not be clear. On 5/24/2017 9:35 AM, Thaddy de Koning wrote: Jonas, sorry for the late response: The implementation is _*not *_undefined for negative values,_unless you say that you define it as undefined_. Because you seem to have implemented it or most of it. It renders a mathematical comparable distribution in the negative to the positive values. In both Turbo Pascal as in Delphi and because they use a different algorithm and made an implementation error as well, the negative values are indeed not defined. But that's because of the algorithm and because of the implementation by Borland (yes, it stems from Borland times). The Mersenne Twister we use is also valid for negative values and if you want I can send you the mathematical proof. I already made the LCG in Delphi compatible mode available on the wiki and that implementation differs in so far as that it corrects the "undefined for negative values" for that algorithm too. It is 100% compatible for the Delphi documented range, btw. I am busy evaluating important Random implementions for different languages, so an FPC library is available for data that is generated in a different language and relies on a particular PRNG. Also note that the output of the current random is strictly valid for 32 bit only. In my code I already added a 64 bit version. Regards, Thaddy On 5/20/2017 2:57 PM, Jonas Maebe wrote: On 20/05/17 14:36, Martin Schreiber wrote: Is this intended? If not, which one is correct? random(x) is undefined for negative parameters. It should have had an unsigned parameter, like in Turbo Pascal (where it is word). Delphi defines it as always returning a positive value, but I don't know what happens if you pass a negative parameter there. Jonas ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
