Re: GMP Problem with % under C++
Miki Hermann writes: I am very well familiar with the % operator in %. Swell. In the document, whose link you sent me, and which I have read before, it is mentioned that Function: mpz_class operator% (mpz_class a, mpz_class d) This means, that the % operator in GMP overloads the usual % operator in C++. Correctamente. Just to recall you, for integer a and b, b > 0, the result of the modulus operator is an integer in the range 0..b-1. If a is negative, the result is equal to (k*b + a) % b for any positive integer k making the expression (k*b + a) positive. By definition for a >= 0 and b > 0, we have a = q*b + (a % b), where q is an integer called quotient. Right, but that is irrelevant since % is not a mathematical modulus operator. Did you not just say you were "very well familiar" with it? Did you *really* read the page Marc pointed you to. This is all mentioned there. Please do read it and get on with your life. -- Torbjörn Please encrypt, key id 0xC8601622 ___ gmp-bugs mailing list gmp-bugs@gmplib.org https://gmplib.org/mailman/listinfo/gmp-bugs
Re: GMP Problem with % under C++
I am very well familiar with the % operator in %. In the document, whose link you sent me, and which I have read before, it is mentioned that Function: mpz_class operator% (mpz_class a, mpz_class d) This means, that the % operator in GMP overloads the usual % operator in C++. Just to recall you, for integer a and b, b > 0, the result of the modulus operator is an integer in the range 0..b-1. If a is negative, the result is equal to (k*b + a) % b for any positive integer k making the expression (k*b + a) positive. By definition for a >= 0 and b > 0, we have a = q*b + (a % b), where q is an integer called quotient. Best regards, Miki On Thu, 2020-11-05 at 22:15 +0100, Marc Glisse wrote: > On Thu, 5 Nov 2020, Miki Hermann wrote: > > > I am not sure if I used the GMP package properly or if I did > > everything > > right, but it seems to me that very probably there is a problem > > somewhere in the GMP package and/or its interface with C++. > > It is very probable that you are not familiar with the % operator in > C or > C++, and that you did not read our documentation at > > https://gmplib.org/manual/C_002b_002b-Interface-Integers > ___ gmp-bugs mailing list gmp-bugs@gmplib.org https://gmplib.org/mailman/listinfo/gmp-bugs
Re: GMP Problem with % under C++
On Fri, Nov 6, 2020 at 8:27 AM Niels Möller wrote: > [snip] > > So your problem really is with % in C++, GMP just follows the > conventions for the builtin integers. > Rather, the OP is expecting that the ''%" operator in his C++ program will behave as mpz_mod() does - which is the same way as the "%" operator behaves in perl. To me, it's not surprising that he would have that expectation. I'm not saying that it's a *reasonable* expectation, as I don't know C++. To the op: If you want to get gmp performance into your perl script, then install Math::GMP and, instead of: use bigint; do: use bigint lib => 'GMP'; ___ gmp-bugs mailing list gmp-bugs@gmplib.org https://gmplib.org/mailman/listinfo/gmp-bugs
Re: GMP Problem with % under C++
Ciao, Il 2020-11-05 22:27 Niels Möller ha scritto: I think this is the same result you get with a plain (64-bit) long. The / and % operators in C++ produce a quotient rounded towards 0, so (f(1) - b) / DECKSIZE == 0, and the corresponding remainder is negative. I'm not that familiar with perl, but I guess it uses the mathematically more sane definition of always rounding the quotient towards -infinity, Every language has its own definition :-) https://en.wikipedia.org/wiki/Modulo_operation#In_programming_languages Ĝis, m ___ gmp-bugs mailing list gmp-bugs@gmplib.org https://gmplib.org/mailman/listinfo/gmp-bugs
Re: GMP Problem with % under C++
Miki Hermann writes: > The result of the command '22b-gmp < 22input.txt' is: > >*** b = 62010736820046 >f(1) - b = -15681174147849 >a = -15681174147849 >On position 2020 is the card 102220661749926 I think this is the same result you get with a plain (64-bit) long. The / and % operators in C++ produce a quotient rounded towards 0, so (f(1) - b) / DECKSIZE == 0, and the corresponding remainder is negative. I'm not that familiar with perl, but I guess it uses the mathematically more sane definition of always rounding the quotient towards -infinity, so that (f(1) - b) / DECKSIZE == -1. So your problem really is with % in C++, GMP just follows the conventions for the builtin integers. I'm not even sure if rounding is specified by the C++ standards, but rounding towards zero is what all C and C++ implementations I'm aware of use. Regards, /Niels -- Niels Möller. PGP-encrypted email is preferred. Keyid 368C6677. Internet email is subject to wholesale government surveillance. ___ gmp-bugs mailing list gmp-bugs@gmplib.org https://gmplib.org/mailman/listinfo/gmp-bugs
Re: GMP Problem with % under C++
On Thu, 5 Nov 2020, Miki Hermann wrote: I am not sure if I used the GMP package properly or if I did everything right, but it seems to me that very probably there is a problem somewhere in the GMP package and/or its interface with C++. It is very probable that you are not familiar with the % operator in C or C++, and that you did not read our documentation at https://gmplib.org/manual/C_002b_002b-Interface-Integers -- Marc Glisse ___ gmp-bugs mailing list gmp-bugs@gmplib.org https://gmplib.org/mailman/listinfo/gmp-bugs
