Ok, so I was able to get the Nim and C++ examples to compile when using the
heap (rather than the stack).
Comparing the code, I think the difference in performance is caused by two
things:
* The Nim code isn't in a main procedure
* The C++ code is using int`s (32 bits) while Nim is using `int`s (64 bits).
Nim's `int type is always the size of a pointer, so you can use it for indexing
arrays.
The time I got for the modified code was about the same:
/tmp $>time ./temp
result: 19999998
real 0m0.847s
user 0m0.792s
sys 0m0.048s
/tmp $>time ./temp_cpp
result: 19999998
real 0m0.905s
user 0m0.851s
sys 0m0.051s
Run
And the code I used:
## compiled with: nim -d:r c filename
## nim v 0.19.9
proc main =
const N = 20_000_000
var data = newSeqUninitialized[int](N)
# custom init
for i in 0 ..< N:
data[i] = i
# busy work
for r in 1 .. 50:
for i in 3 ..< N-1:
data[i] = (data[i+1]-data[i])+data[i-1]
echo "result: ",data[N-2]
main()
Run
// compiled with: c++ -O3 -o filename filename.cpp
#include <iostream>
const int N = 20000000;
int main()
{
size_t* data = new size_t[N];
// custom init
for (size_t i=0; i<N; i++) {
data[i] = i;
}
// busy work
for (size_t r=0; r<50; r++) {
for (size_t i=3; i<N-1; i++)
{
data[i] = (data[i+1]+data[i-1]) / 2;
}
}
std::cout << "result: " << data[N-2] << std::endl;
return ( 0 );
}
Run
