Quicksort algorithm in-place crashes after some iterations - c

Question

I have implemented the following quicksort algorithm to sort couples of points(3D space).
Every couple defines a line: the purpose is to place all lines that have a distance less or equal to powR nearby inside the array which contains all the couples.
The Array containing coordinates is monodimentional, every 6 elements define a couple and every 3 a point.
When i run the algorithm with an array of 3099642 elements stops after processing 2799222 trying to enter the next iteration. if i start the algorithm from element 2799228 it stops at 3066300.
I can't figure out where is the problem, and suggestion?
void QuickSort(float *array, int from, int to, float powR){
float pivot[6];
float temp[6];
float x1;
float y1;
float z1;
float x2;
float y2;
float z2;
float d12;
int i;
int j;
if(from >= to)
return;
pivot[0] = array[from+0];
pivot[1] = array[from+1];
pivot[2] = array[from+2];
pivot[3] = array[from+3];
pivot[4] = array[from+4];
pivot[5] = array[from+5];
i = from;
for(j = from+6; j <= to; j += 6){
x1 = pivot[0] - array[j+0];
y1 = pivot[1] - array[j+1];
z1 = pivot[2] - array[j+2];
x2 = pivot[3] - array[j+3];
y2 = pivot[4] - array[j+4];
z2 = pivot[5] - array[j+5];
d12 = (x1*x1 + y1*y1 + z1*z1) + (x2*x2 + y2*y2 + z2*z2);
/*the sorting condition i am using is the regular euclidean norm*/
if (d12 <= powR){
i += 6;
temp[0] = array[i+0];
temp[1] = array[i+1];
temp[2] = array[i+2];
temp[3] = array[i+3];
temp[4] = array[i+4];
temp[5] = array[i+5];
array[i+0] = array[j+0];
array[i+1] = array[j+1];
array[i+2] = array[j+2];
array[i+3] = array[j+3];
array[i+4] = array[j+4];
array[i+5] = array[j+5];
array[j+0] = temp[0];
array[j+1] = temp[1];
array[j+2] = temp[2];
array[j+3] = temp[3];
array[j+4] = temp[4];
array[j+5] = temp[5];
}
}
QuickSort(array, i+6, to, powR);
}
function is called in this way:
float LORs = (float) calloc((unsigned)tot, sizeof(float));
LORs is filled reading datas from a file, and works fine.
QuickSort(LORs, 0, 6000, powR);
free(LORs);

Answer 1

for(j = from+6; j <= to; j += 6) {
array[i+0] = array[j+0];
array[i+1] = array[j+1];
array[i+2] = array[j+2];
array[i+3] = array[j+3];
array[i+4] = array[j+4];
array[i+5] = array[j+5];
}
Your j + constant_number goes out of bounds when you approach the end. That's why it crashes at the end. Note that constant_number is non-negative.
When j comes close (how close you can find by the increment step, i.e. +6) to the end of your array, it will go for sure out of bounds.
Take the easy case, the max value j can get. That is the size of your array.
So, let's call it N.
Then, when j is equal to N, you are going to enter the loop.
Then, you want to access array[j + 0], which is actually array[N + 0], which is array[N].
I am pretty sure, you know that indexing in C (which you should in the future include in the tags of your questions is needed), is from 0 to N - 1. And so on..
EDIT: As the comments suggest, this is not a (quick)sort!
I had implemented quickSort here, is you want to take an idea of it. I suggest you start from the explanations and not from the code!