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!-------------------------------------------------------------------------------
!
! This file is part of the WSPR application, Weak Signal Propogation Reporter
!
! File Name: ssort.f90
! Description: Sort an array and optionally make the same interchanges in
! an auxiliary array.
!
! Copyright (C) 2001-2014 Joseph Taylor, K1JT
! License: GPL-3+
!
! This program is free software; you can redistribute it and/or modify it under
! the terms of the GNU General Public License as published by the Free Software
! Foundation; either version 3 of the License, or (at your option) any later
! version.
!
! This program is distributed in the hope that it will be useful, but WITHOUT
! ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
! FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
! details.
!
! You should have received a copy of the GNU General Public License along with
! this program; if not, write to the Free Software Foundation, Inc., 51 Franklin
! Street, Fifth Floor, Boston, MA 02110-1301, USA.
!
!-------------------------------------------------------------------------------
subroutine ssort (x,y,n,kflag)
! Purpose: Sort an array and optionally make the same interchanges in
! an auxiliary array. The array may be sorted in increasing
! or decreasing order. A slightly modified quicksort
! algorithm is used.
! x - array of values to be sorted
! y - array to be (optionally) carried along
! n - number of values in array x to be sorted
! kflag - control parameter
! = 2 means sort x in increasing order and carry y along.
! = 1 means sort x in increasing order (ignoring y)
! = -1 means sort x in decreasing order (ignoring y)
! = -2 means sort x in decreasing order and carry y along.
integer kflag, n
real x(n), y(n)
real r, t, tt, tty, ty
integer i, ij, j, k, kk, l, m, nn
integer il(21), iu(21)
nn = n
if (nn .lt. 1) then
print*,'ssort: The number of sort elements is not positive.'
print*,'ssort: n = ',nn,' kflag = ',kflag
return
endif
kk = abs(kflag)
if (kk.ne.1 .and. kk.ne.2) then
print *,'The sort control parameter, k, is not 2, 1, -1, or -2.'
return
endif
! Alter array x to get decreasing order if needed
if (kflag .le. -1) then
do i=1,nn
x(i) = -x(i)
enddo
endif
if (kk .eq. 2) go to 100
! Sort x only
m = 1
i = 1
j = nn
r = 0.375e0
20 if (i .eq. j) go to 60
if (r .le. 0.5898437e0) then
r = r+3.90625e-2
else
r = r-0.21875e0
endif
30 k = i
! Select a central element of the array and save it in location t
ij = i + int((j-i)*r)
t = x(ij)
! If first element of array is greater than t, interchange with t
if (x(i) .gt. t) then
x(ij) = x(i)
x(i) = t
t = x(ij)
endif
l = j
! If last element of array is less than than t, interchange with t
if (x(j) .lt. t) then
x(ij) = x(j)
x(j) = t
t = x(ij)
! If first element of array is greater than t, interchange with t
if (x(i) .gt. t) then
x(ij) = x(i)
x(i) = t
t = x(ij)
endif
endif
! Find an element in the second half of the array which is smaller than t
40 l = l-1
if (x(l) .gt. t) go to 40
! Find an element in the first half of the array which is greater than t
50 k = k+1
if (x(k) .lt. t) go to 50
! Interchange these elements
if (k .le. l) then
tt = x(l)
x(l) = x(k)
x(k) = tt
go to 40
endif
! Save upper and lower subscripts of the array yet to be sorted
if (l-i .gt. j-k) then
il(m) = i
iu(m) = l
i = k
m = m+1
else
il(m) = k
iu(m) = j
j = l
m = m+1
endif
go to 70
! Begin again on another portion of the unsorted array
60 m = m-1
if (m .eq. 0) go to 190
i = il(m)
j = iu(m)
70 if (j-i .ge. 1) go to 30
if (i .eq. 1) go to 20
i = i-1
80 i = i+1
if (i .eq. j) go to 60
t = x(i+1)
if (x(i) .le. t) go to 80
k = i
90 x(k+1) = x(k)
k = k-1
if (t .lt. x(k)) go to 90
x(k+1) = t
go to 80
! Sort x and carry y along
100 m = 1
i = 1
j = nn
r = 0.375e0
110 if (i .eq. j) go to 150
if (r .le. 0.5898437e0) then
r = r+3.90625e-2
else
r = r-0.21875e0
endif
120 k = i
! Select a central element of the array and save it in location t
ij = i + int((j-i)*r)
t = x(ij)
ty = y(ij)
! If first element of array is greater than t, interchange with t
if (x(i) .gt. t) then
x(ij) = x(i)
x(i) = t
t = x(ij)
y(ij) = y(i)
y(i) = ty
ty = y(ij)
endif
l = j
! If last element of array is less than t, interchange with t
if (x(j) .lt. t) then
x(ij) = x(j)
x(j) = t
t = x(ij)
y(ij) = y(j)
y(j) = ty
ty = y(ij)
! If first element of array is greater than t, interchange with t
if (x(i) .gt. t) then
x(ij) = x(i)
x(i) = t
t = x(ij)
y(ij) = y(i)
y(i) = ty
ty = y(ij)
endif
endif
! Find an element in the second half of the array which is smaller than t
130 l = l-1
if (x(l) .gt. t) go to 130
! Find an element in the first half of the array which is greater than t
140 k = k+1
if (x(k) .lt. t) go to 140
! Interchange these elements
if (k .le. l) then
tt = x(l)
x(l) = x(k)
x(k) = tt
tty = y(l)
y(l) = y(k)
y(k) = tty
go to 130
endif
! Save upper and lower subscripts of the array yet to be sorted
if (l-i .gt. j-k) then
il(m) = i
iu(m) = l
i = k
m = m+1
else
il(m) = k
iu(m) = j
j = l
m = m+1
endif
go to 160
! Begin again on another portion of the unsorted array
150 m = m-1
if (m .eq. 0) go to 190
i = il(m)
j = iu(m)
160 if (j-i .ge. 1) go to 120
if (i .eq. 1) go to 110
i = i-1
170 i = i+1
if (i .eq. j) go to 150
t = x(i+1)
ty = y(i+1)
if (x(i) .le. t) go to 170
k = i
180 x(k+1) = x(k)
y(k+1) = y(k)
k = k-1
if (t .lt. x(k)) go to 180
x(k+1) = t
y(k+1) = ty
go to 170
! Clean up
190 if (kflag .le. -1) then
do i=1,nn
x(i) = -x(i)
enddo
endif
return
end subroutine ssort
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