void build_kdtree(kdxptr kd, int nbucket)
{
int k, n, i, d, m, j, ct;
kdnode *ntab;
n = kd->ngas;
k = 1;
while (n > nbucket) {
n = n>>1;
k = k<<1;
}
kd->nnode = k<<1;
kd->nsplit = k;
ntab = kd->ntab = (kdnode *) allocate(kd->nnode * sizeof(kdnode));
ntab[KDROOT].first = 0; /* initialize root node */
ntab[KDROOT].last = kd->ngas-1;
ntab[KDROOT].bnd = kd->bnd;
i = KDROOT;
ct = KDROOT;
SetNext(ct);
for ( ; ; ) { /* loop splitting nodes */
if (i < kd->nsplit) {
d = 0; /* find longest dimension */
for (j=1; j<3; ++j) {
if (ntab[i].bnd.maxb[j]-ntab[i].bnd.minb[j] >
ntab[i].bnd.maxb[d]-ntab[i].bnd.minb[d])
d = j;
}
m = median_index(kd->bptr, d, ntab[i].first, ntab[i].last);
ntab[i].dim = d;
ntab[i].split = Pos(kd->bptr[m])[d];
ntab[Lower(i)].bnd = ntab[i].bnd;
ntab[Lower(i)].bnd.maxb[d] = ntab[i].split;
ntab[Lower(i)].first = ntab[i].first;
ntab[Lower(i)].last = m-1;
ntab[Upper(i)].bnd = ntab[i].bnd;
ntab[Upper(i)].bnd.minb[d] = ntab[i].split;
ntab[Upper(i)].first = m;
ntab[Upper(i)].last = ntab[i].last;
i = Lower(i);
} else {
ntab[i].dim = -1;
SetNext(i);
if (i == ct) break;
}
}
upward_pass(kd, KDROOT);
}
//k[0,1,2,3...]
int select_kth_smallest(const int *A, int len, int k) {
int *medians, *tempA, *tempAA;
int groupCount;
int lastGroupElementCount;
int i, j, median;
int pivotElem;
pivot_t pivot;
//pivot_t span;
if (len <= 1) {
return A[0];
}
if (len % SELECTGROUPCOUNT == 0) {
groupCount = len / SELECTGROUPCOUNT;
lastGroupElementCount = SELECTGROUPCOUNT;
} else {
groupCount = len / SELECTGROUPCOUNT + 1;
lastGroupElementCount = len % SELECTGROUPCOUNT;
}
medians = (int*)malloc(sizeof(int) * groupCount);
tempA = (int*)malloc(sizeof(int) * len);
memcpy(tempA, A, sizeof(int) * len);
j = 0;
for (i=0; i<groupCount-1; i++) {
int start = i * SELECTGROUPCOUNT;
insertion_sort(tempA, start, start+SELECTGROUPCOUNT);
median = tempA[median_index(SELECTGROUPCOUNT) + start];
medians[j++] = median;
}
// for last group
insertion_sort(tempA, i * SELECTGROUPCOUNT, lastGroupElementCount);
median = tempA[median_index(lastGroupElementCount) + i * SELECTGROUPCOUNT];
medians[j] = median;
pivotElem = select_kth_smallest(medians, groupCount, median_index(groupCount));
pivot = median_partition_equal(tempA, 0, len, pivotElem);
if (medians) {
free(medians);
medians = NULL;
}
if (k >= pivot.q && k < pivot.t) {
i = tempA[pivot.q];
if(tempA) {
free(tempA);
tempA = NULL;
}
return i;
}
else if (k >= pivot.t) {
tempAA = malloc(sizeof(int) * (len - pivot.t));
memcpy(tempAA, tempA+pivot.t, sizeof(int) * (len-pivot.t));
if (tempA) {
free(tempA);
tempA = NULL;
}
i = select_kth_smallest(tempAA, len-pivot.t, k-pivot.t);
if (tempAA) {
free(tempAA);
tempAA = NULL;
}
return i;
} else {
tempAA = malloc(sizeof(int) * (pivot.q));
memcpy(tempAA, tempA, sizeof(int) * (pivot.q));
if (tempA) {
free(tempA);
tempA = NULL;
}
i = select_kth_smallest(tempAA, pivot.q, k);
if (tempAA) {
free(tempAA);
tempAA = NULL;
}
return i;
}
}
