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include <mach.h>
include <ctype.h>
include <error.h>
include <gset.h>
include <pkg/rg.h>
include "pdm.h"
# PDM_RANPERM -- Make a random permutation of the data vector.
# This is the algorithm:
# Starting at the beginning of the input array,
# Do this numdatapoints times {
# Find the next random position.
# Call urand for a random number between one and numdatapoints(hash).
# Move forward in the input array this number of places (mod numpts).
# While (marker array for this position has a zero) {
# Move to the next position (linear rehash).
# }
# Put the input array value found at this position into the
# output array, set the marker array value corresponding
# to this position to zero.
# }
procedure pdm_ranperm (inarray, inuse, outarray, outinuse, numpts, seed)
int numpts # number of points in the data
double inarray[numpts] # data to be permuted
double outarray[numpts] # output permuted data to this array
int inuse[numpts] # the PDM in-use array
int outinuse[numpts] # output scrambled in-use array
long seed # a seed for the random number generator
int count, pos
real urand()
pointer p, sp # array to keep track of which have been used
begin
# Allocate the output array and the marker array.
# Fill the marker array with ones (amovki)
call smark (sp)
call salloc (p, numpts, TY_INT)
call amovki (1, Memi[p], numpts) # Set this array to all ones.
pos = 0
do count = 1, numpts {
pos = mod(pos+int(urand(seed)*numpts)+1, numpts) # Hash.
while (Memi[p+pos] == 0) # Linear rehash.
pos = mod(pos+1, numpts)
outarray[count] = inarray[pos+1]
outinuse[count] = inuse[pos+1]
Memi[p+pos] = 0
}
call sfree (sp)
end
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