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psblas3/base/serial/aux/mrgsrt.f

235 lines
11 KiB
FortranFixed

C
C Parallel Sparse BLAS v2.0
C (C) Copyright 2006 Salvatore Filippone University of Rome Tor Vergata
C Alfredo Buttari University of Rome Tor Vergata
C
C Redistribution and use in source and binary forms, with or without
C modification, are permitted provided that the following conditions
C are met:
C 1. Redistributions of source code must retain the above copyright
C notice, this list of conditions and the following disclaimer.
C 2. Redistributions in binary form must reproduce the above copyright
C notice, this list of conditions, and the following disclaimer in the
C documentation and/or other materials provided with the distribution.
C 3. The name of the PSBLAS group or the names of its contributors may
C not be used to endorse or promote products derived from this
C software without specific written permission.
C
C THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
C ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
C TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
C PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE PSBLAS GROUP OR ITS CONTRIBUTORS
C BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
C CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
C SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
C INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
C CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
C ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
C POSSIBILITY OF SUCH DAMAGE.
C
C
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***********************************************************************
* *
* FUNCTION = This subroutine returns an array of pointers, L, *
* to be used to sort the integer input vector K; *
* the routine implements a list merge-sort *
* *
***********************************************************************
* *
* CALL MRGSRT(N,K,L,IRET) *
* *
* INPUT = *
* *
* SYMBOLIC NAME: N *
* POSITION: First parameter. *
* ATTRIBUTES: INTEGER *
* VALUES: >= 0 *
* DESCRIPTION: Dimension of the array to be sorted *
* *
* SYMBOLIC NAME: K *
* POSITION: Second parameter *
* ATTRIBUTES: INTEGER ARRAY(N) *
* VALUES: Any *
* DESCRIPTION: Input array containing the keys, i.e., values *
* to be sorted *
* *
* *
* *
* OUTPUT = *
* *
* SYMBOLIC NAME: L *
* POSITION: Third parameter *
* ATTRIBUTES: INTEGER ARRAY(N+2) *
* VALUES: >= 0 *
* DESCRIPTION: On exit, this array contains pointers to *
* the keys array. *
* *
***********************************************************************
***********************************************************************
* *
***********************************************************************
***********************************************************************
* ALGORITHM DESCRIPTION *
* *
* REFERENCES = (1) D. E. Knuth *
* The Art of Computer Programming, *
* vol.3: Sorting and Searching *
* Addison-Wesley, 1973 *
* *
* FUNCTION = This subroutine is based on the well-known merge-sort *
* algorithm; according to (1) we are sorting 'records' *
* R(I) with respect to keys K(I), and to this purpose *
* we use 'links' L(I); at the end of the subroutine, *
* L(0) is the index of the first record in the sorted *
* sequence, then for every record R(I), we have into *
* L(I) the index of the next one in the sequence. A *
* value L(I)=0 signals the end of the sequence. *
* The sorting is stable, i.e., if K(I)=K(J) and I<J, *
* then in the sorted sequence R(I) precedes R(J); many *
* sorting algorithms, e.g. quicksort, are not stable. *
* The list merge-sort is one of the fastest stable *
* sortings available; it is guaranteed to run in *
* O(N log N) time on both the average and worst cases. *
* *
* *
***********************************************************************
***********************************************************************
* ALGORITHM EXAMPLE(S) *
* *
* EXAMPLE: Construct a sorted array of records RS from a vector R *
* according to the keys stored in K *
* *
* CALL MRGSRT(N,K,L,*100) *
* I = L(0) *
* DO 100 J = 1, N *
* RS(J) = R(I) *
* I = L(I) *
* 100 CONTINUE ! RETURN POINT IF ARRAY ALREADY SORTED *
* *
* *
* EXAMPLE: Sort in place array R *
* *
* CALL MRGSRT(N,K,L,*400) *
* LP = L(0) *
* KK = 1 *
* 100 CONTINUE *
* IF ((LP.EQ.0).OR.(KK.GT.N)) GOTO 400 *
* 200 CONTINUE *
* IF (LP.GE.KK) GOTO 300 *
* LP = L(LP) *
* GOTO 200 *
* 300 CONTINUE *
* SWAP = R(KK) *
* R(KK) = R(LP) *
* R(LP) = SWAP *
* LSWAP = L(LP) *
* L(LP) = L(KK) *
* L(KK) = LP *
* LP = LSWAP *
* KK = KK+1 *
* GOTO 100 *
* 400 CONTINUE *
* *
* *
***********************************************************************
SUBROUTINE MRGSRT(N,K,L,IRET)
C .. Scalar Arguments ..
INTEGER N, IRET
C ..
C .. Array Arguments ..
INTEGER K(N),L(0:N+1)
C ..
C .. Local Scalars ..
INTEGER P,Q,S,T
C ..
C .. Intrinsic Functions ..
INTRINSIC IABS,ISIGN
C ..
IRET = 0
C First step: we are preparing ordered sublists, exploiting
C what order was already in the input data; negative links
C mark the end of the sublists
L(0) = 1
T = N + 1
DO P = 1,N - 1
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IF (K(P).LE.K(P+1)) THEN
L(P) = P + 1
ELSE
L(T) = - (P+1)
T = P
END IF
END DO
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L(T) = 0
L(N) = 0
C See if the input was already sorted
IF (L(N+1).EQ.0) THEN
IRET = 1
RETURN
ELSE
L(N+1) = IABS(L(N+1))
END IF
200 CONTINUE
C Otherwise, begin a pass through the list.
C Throughout all the subroutine we have:
C P, Q: pointing to the sublists being merged
C S: pointing to the most recently processed record
C T: pointing to the end of previously completed sublist
S = 0
T = N + 1
P = L(S)
Q = L(T)
IF (Q.EQ.0) RETURN
300 CONTINUE
IF (K(P).GT.K(Q)) GO TO 600
400 CONTINUE
L(S) = ISIGN(P,L(S))
S = P
P = L(P)
IF (P.GT.0) GO TO 3100
C Otherwise, one sublist ended, and we append to it the rest
C of the other one.
500 CONTINUE
L(S) = Q
S = T
550 CONTINUE
T = Q
Q = L(Q)
IF (Q.GT.0) GO TO 550
GO TO 800
600 CONTINUE
L(S) = ISIGN(Q,L(S))
S = Q
Q = L(Q)
IF (Q.GT.0) GO TO 3200
700 CONTINUE
L(S) = P
S = T
750 CONTINUE
T = P
P = L(P)
IF (P.GT.0) GO TO 750
800 CONTINUE
P = -P
Q = -Q
IF (Q.EQ.0) THEN
L(S) = ISIGN(P,L(S))
L(T) = 0
GO TO 200
ELSE
GO TO 300
END IF
3100 CONTINUE
IF (K(P).GT.K(Q)) GO TO 600
S = P
P = L(P)
IF (P.GT.0) GO TO 3100
GO TO 500
3200 CONTINUE
IF (K(P).LE.K(Q)) GO TO 400
S = Q
Q = L(Q)
IF (Q.GT.0) GO TO 3200
GO TO 700
END