mersenneforum.org - View Single Post - Init GMP variable with char or bit shift?

hunson · 2021-11-25, 15:46

Hi,

I started learning C a couple of days ago and thought it might be fun to make use of the speed of C and learn the language with an 'useful' application: calculating with GMP.
I played around with some functions and thought it might be fun to generate huge solinas numbers (2^a +/- 2^b +/-1).

I calculated the 2^x terms with mpz_pow_ui() individually and added them. This works fine so far. Then I realized that these numbers have a special form in base 2 (e.g. 2^10+2^6-1 = 10000111111). So they might be generated way faster by bit shifting or construction of a 'bit' char/string than doing the mpz_pow_ui() calculations for large exponents.

Now my questions is: Is there a way to import/convert a char into a mpz_t variable for further calculation? I tried mzp_set_str() base 2 but I can not make it work if I construct the char variable with a loop. A predefined variable like char *num = "10000000000"; gives the correct number of 1024, but no further manipulation is possible.

Any help or pointing in the right direction is very much appreciated.

hunsun

2021-11-25, 15:46	#1
hunson Feb 2020 Germany 2·5² Posts	Init GMP variable with char or bit shift? Hi, I started learning C a couple of days ago and thought it might be fun to make use of the speed of C and learn the language with an 'useful' application: calculating with GMP. I played around with some functions and thought it might be fun to generate huge solinas numbers (2^a +/- 2^b +/-1). I calculated the 2^x terms with mpz_pow_ui() individually and added them. This works fine so far. Then I realized that these numbers have a special form in base 2 (e.g. 2^10+2^6-1 = 10000111111). So they might be generated way faster by bit shifting or construction of a 'bit' char/string than doing the mpz_pow_ui() calculations for large exponents. Now my questions is: Is there a way to import/convert a char into a mpz_t variable for further calculation? I tried mzp_set_str() base 2 but I can not make it work if I construct the char variable with a loop. A predefined variable like char *num = "10000000000"; gives the correct number of 1024, but no further manipulation is possible. Any help or pointing in the right direction is very much appreciated. hunsun