Strange running times in C++ loops -

so, i'm writing program, optimization key factor. however: during optimization, notice function considered relatively simple, taking way long run. since, in comparison, more difficult function taking way shorter.

whole relevant section

// simple function  int get_chunk_index(std::vector<chunk> chunks, int x, int y) {     glm::vec3 target = glm::vec3(x * 40, 0, y * 40);     (int = 0; < chunks.size(); i++) {         if (chunks[i].trans.getpos() == target) {             return i;         }     }     return -1; }  // end simple function 

if more functions, feel free ask, quite large program, can't include everything here.

ps: chunks ever 0->40 in size.

a few simple options.

1) chunks being passed value, creates complete copy of vector being passed. try passing const reference (i.e. const std::vector<chunk> &chunk) instead.

2) rather passing x , y, , creating glm::vec3 (whatever - it's non-standard) them, change function accept glm::vec3 reference. forces caller create object, allows caller control updating of (rather recreating new object every time).

3) take evaluation of chunks.size() out of loop, , use preincrement (won't create temporary) rather post-increment.

std::size_t size = chunks.size(); (int = 0; < size; ++i) {     if (chunks[i].trans.getpos() == target)     {         return i;     } } 

4) consider using iterators rather array indexing.

std::vector<chunk>::const_iterator i, begin = chunks.begin(), end = chunks.end();  (i = begin; != end; ++i)    if (i->trans.getpos() == target) return std::distance(begin, i); 

or (c++11 , later)

for (const auto &i : chunks) {     if (i.trans.getpos() == target) return std::distance(chunks.begin(), i); } 

5) instead of passing vector, pass begin , end iterators. allow more simplification of loop.

6) check getpos() function being called doing, , optimise that.

7) timing measurements optimisation turned on, , them across large number of calls of function. performance measurements of individual function calls don't mean in practice (the jitter in other things affect performance dominate measurements).

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