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define LOGPTR 20 # log2(maxpts) (1e6)
# AT_QSORTD -- Vector Quicksort. In this version the index array is sorted.
# The input and output index array may be the same.
procedure at_qsortd (data, a, b, npix)
double data[ARB] #I the input data array
int a[ARB] #I the input index array
int b[ARB] #O the output index array
int npix #I the number of pixels
int i, j, lv[LOGPTR], p, uv[LOGPTR], temp
double pivot
begin
# Initialize the indices for an inplace sort.
do i = 1, npix
a[i] = i
call amovi (a, b, npix)
p = 1
lv[1] = 1
uv[1] = npix
while (p > 0) {
# If only one elem in subset pop stack otherwise pivot line.
if (lv[p] >= uv[p])
p = p - 1
else {
i = lv[p] - 1
j = uv[p]
pivot = data[b[j]]
while (i < j) {
for (i=i+1; data[b[i]] < pivot; i=i+1)
;
for (j=j-1; j > i; j=j-1)
if (data[b[j]] <= pivot)
break
if (i < j) { # out of order pair
temp = b[j] # interchange elements
b[j] = b[i]
b[i] = temp
}
}
j = uv[p] # move pivot to position i
temp = b[j] # interchange elements
b[j] = b[i]
b[i] = temp
if (i-lv[p] < uv[p] - i) { # stack so shorter done first
lv[p+1] = lv[p]
uv[p+1] = i - 1
lv[p] = i + 1
} else {
lv[p+1] = i + 1
uv[p+1] = uv[p]
uv[p] = i - 1
}
p = p + 1 # push onto stack
}
}
end
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