GNU MP: Cannot reallocate memory - Why? - Page 2

hunson · 2022-01-17, 21:16

Thanks for looking into my code.

I was already writing a reply where I explained that I do not understand the problem and I could not figure it out when I decided to have a look if someone else answered after henryzz :)

I even had it running with the

Code:

primes = malloc(sizeof(int) * sieve_depth);

in 'debug' but not in 'release', something was very strange.

I corrected the corresponding lines and the code works! Thanks.

I tried to save some memory, so I used a char variable to store the information from the sieve. Worked out great for me...

Now I can try out my 'efficient' program to generate prime candidates

bsquared · 2022-01-17, 21:23

Speaking of efficiency, it is much better to flip the order of the loops. Exponentiation and the other operations on big numbers are a lot more expensive than division by a single limb, so do the loop over 'e' first. Then after you've computed each candidate 'n', loop over the primes and trial divide, breaking out if mod==0.

hunson · 2022-01-18, 20:50

Thanks for the bug finding! The program works as expected now.
@bsquared: I wrote the program with flipped for-loops in the beginning. Then I switched to see what the performance might be, encountered the bug and forgot to change it back :/

*now* I can use my efficient program (I actually find it quite alright for a novice)

regards

2022-01-17, 21:16	#12
hunson Feb 2020 Germany 110010₂ Posts	Thanks for looking into my code. I was already writing a reply where I explained that I do not understand the problem and I could not figure it out when I decided to have a look if someone else answered after henryzz :) I even had it running with the Code: primes = malloc(sizeof(int) * sieve_depth); in 'debug' but not in 'release', something was very strange. I corrected the corresponding lines and the code works! Thanks. I tried to save some memory, so I used a char variable to store the information from the sieve. Worked out great for me... Now I can try out my 'efficient' program to generate prime candidates

2022-01-17, 21:23	#13
bsquared "Ben" Feb 2007 3,617 Posts	Speaking of efficiency, it is much better to flip the order of the loops. Exponentiation and the other operations on big numbers are a lot more expensive than division by a single limb, so do the loop over 'e' first. Then after you've computed each candidate 'n', loop over the primes and trial divide, breaking out if mod==0. Last fiddled with by bsquared on 2022-01-17 at 21:24

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2022-01-18, 20:50	#14
hunson Feb 2020 Germany 2·5² Posts	Thanks for the bug finding! The program works as expected now. @bsquared: I wrote the program with flipped for-loops in the beginning. Then I switched to see what the performance might be, encountered the bug and forgot to change it back :/ now I can use my efficient program (I actually find it quite alright for a novice) regards