Question

In my app I have to store path points into an array and then follow those points. To get a smoother run I usually have to dump a path into 5k points. This means I have to store 10k floats- 5k for x and 5k for y coordinates. Right now this is what I’m doing:

1.In the view load I initialize an NSArray with those 10k numbers like this:

pathPoints=[NSArray arrayWithObjects:[NSNumber numberWithFloat:-134.8427],  [NSNumber numberWithFloat:148.8433], ....... and so on];

1. And then I read it like this:

   int currentXIndex=..////

   [[pathPoints objectAtIndex:currentXIndex] floatValue];

   [[pathPoints objectAtIndex:currentXIndex+1] floatValue];

As you can see, each time when I need the next position? I have to unbox it(cast it from NSNumber to float). And I’m sure this takes a great deal of performance. Any suggestions how I can do this another, more performant way?

Answer 1

For a simple container, I’d use a C array and traverse with pointers. Remember that Objective C is a superset of C, so you have everything right there for when the need arise.

edit; sample code:

you don’t have to store all numbers ‘naked’, a struct don’t have any overhead:

typedef struct tCoords {
    float x, y;
} tCoords;

then just malloc() the size needed:

arraySize = 5000;
tCoords *array = malloc(arraySize * sizeof(tCoords));

and iterate like any simple array:

tCoords *end = array+arraySize;

for (tCoords *p = array; p<end; ++p) {
    float x = p->x;
    float y = p->y;
}

If you don’t like the “old C” look of the code, it’s easy to encapsulate all this in a class that ‘owns’ the array (don’t forget to free() it when disposed)