In C long is only guaranteed to be at least 32 bits (IIRC it's 64 bits on 64-bit *nix but 32-bit on 64-bit Windows). long long is guaranteed to be at least 64 bits (and is 64 bits on all systems I know of).
Simon On Tuesday, January 14, 2014 5:46:04 PM UTC-5, Przemyslaw Szufel wrote: > > Simon, > Thanks for the explanation! > In Java int is 32 bit as well. > I have just replaced ints with longs in Java and found out that now I get > the Java speed also very similar to Julia. > > However I tried in Cython: > def primes_list(int kmax): > cdef int k, i > cdef long n > cdef long p[20000] > ... > > and surprisingly the speed did not change...at first I thought that maybe > something did not compile or is in cache - but I made sure - it's not the > cache. > Cython speed remains unchanged regardles using int or long? > I know that now it becomes other language question...but maybe someone can > explain? > > All best, > Przemyslaw Szufel > > > On Tuesday, 14 January 2014 23:29:40 UTC+1, Simon Kornblith wrote: >> >> With a 64-bit build, Julia integers are 64-bit unless otherwise >> specified. In C, you use ints, which are 32-bit. Changing them to long long >> makes the C code perform similarly to the Julia code on my system. >> Unfortunately, it's hard to operate on 32-bit integers in Julia, since + >> promotes to 64-bit by default (am I missing something)? >> >> Simon >> >> On Tuesday, January 14, 2014 4:32:16 PM UTC-5, Przemyslaw Szufel wrote: >>> >>> Dear Julia users, >>> >>> I am considering using Julia for computational projects. >>> As a first to get a feeling of the new language a I tried to benchmark >>> Julia speed against other popular languages. >>> I used an example code from the Cython tutorial: >>> http://docs.cython.org/src/tutorial/cython_tutorial.html [ the code for >>> finding n first prime numbers]. >>> >>> Rewriting the code in different languages and measuring the times on my >>> Windows laptop gave me the following results: >>> >>> Language | Time in seconds (less=better) >>> >>> Python: 65.5 >>> Cython (with MinGW): 0.82 >>> Java : 0.64 >>> Java (with -server option) : 0.64 >>> C (with MinGW): 0.64 >>> Julia (0.2): 2.1 >>> Julia (0.3 nightly build): 2.1 >>> >>> All the codes for my experiments are attached to this post (Cython i >>> Python are both being run starting from the prim.py file) >>> >>> The thing that worries me is that Julia takes much much longer than >>> Cython ,,, >>> I am a beginner to Julia and would like to kindly ask what am I doing >>> wrong with my code. >>> I start Julia console and use the command include ("prime.jl") to >>> execute it. >>> >>> This code looks very simple and I think the compiler should be able to >>> optimise it to at least the speed of Cython? >>> Maybe I my code has been written in non-Julia style way and the compiler >>> has problems with it? >>> >>> I will be grateful for any answers or comments. >>> >>> Best regards, >>> Przemyslaw Szufel >>> >>
