*DECK HPSORT
SUBROUTINE HPSORT (HX, N, STRBEG, STREND, IPERM, KFLAG, WORK, IER)
C***BEGIN PROLOGUE HPSORT
C***PURPOSE Return the permutation vector generated by sorting a
C substring within a character array and, optionally,
C rearrange the elements of the array. The array may be
C sorted in forward or reverse lexicographical order. A
C slightly modified quicksort algorithm is used.
C***LIBRARY SLATEC
C***CATEGORY N6A1C, N6A2C
C***TYPE CHARACTER (SPSORT-S, DPSORT-D, IPSORT-I, HPSORT-H)
C***KEYWORDS PASSIVE SORTING, SINGLETON QUICKSORT, SORT, STRING SORTING
C***AUTHOR Jones, R. E., (SNLA)
C Rhoads, G. S., (NBS)
C Sullivan, F. E., (NBS)
C Wisniewski, J. A., (SNLA)
C***DESCRIPTION
C
C HPSORT returns the permutation vector IPERM generated by sorting
C the substrings beginning with the character STRBEG and ending with
C the character STREND within the strings in array HX and, optionally,
C rearranges the strings in HX. HX may be sorted in increasing or
C decreasing lexicographical order. A slightly modified quicksort
C algorithm is used.
C
C IPERM is such that HX(IPERM(I)) is the Ith value in the
C rearrangement of HX. IPERM may be applied to another array by
C calling IPPERM, SPPERM, DPPERM or HPPERM.
C
C An active sort of numerical data is expected to execute somewhat
C more quickly than a passive sort because there is no need to use
C indirect references. But for the character data in HPSORT, integers
C in the IPERM vector are manipulated rather than the strings in HX.
C Moving integers may be enough faster than moving character strings
C to more than offset the penalty of indirect referencing.
C
C Description of Parameters
C HX - input/output -- array of type character to be sorted.
C For example, to sort a 80 element array of names,
C each of length 6, declare HX as character HX(100)*6.
C If ABS(KFLAG) = 2, then the values in HX will be
C rearranged on output; otherwise, they are unchanged.
C N - input -- number of values in array HX to be sorted.
C STRBEG - input -- the index of the initial character in
C the string HX that is to be sorted.
C STREND - input -- the index of the final character in
C the string HX that is to be sorted.
C IPERM - output -- permutation array such that IPERM(I) is the
C index of the string in the original order of the
C HX array that is in the Ith location in the sorted
C order.
C KFLAG - input -- control parameter:
C = 2 means return the permutation vector resulting from
C sorting HX in lexicographical order and sort HX also.
C = 1 means return the permutation vector resulting from
C sorting HX in lexicographical order and do not sort
C HX.
C = -1 means return the permutation vector resulting from
C sorting HX in reverse lexicographical order and do
C not sort HX.
C = -2 means return the permutation vector resulting from
C sorting HX in reverse lexicographical order and sort
C HX also.
C WORK - character variable which must have a length specification
C at least as great as that of HX.
C IER - output -- error indicator:
C = 0 if no error,
C = 1 if N is zero or negative,
C = 2 if KFLAG is not 2, 1, -1, or -2,
C = 3 if work array is not long enough,
C = 4 if string beginning is beyond its end,
C = 5 if string beginning is out-of-range,
C = 6 if string end is out-of-range.
C
C E X A M P L E O F U S E
C
C CHARACTER*2 HX, W
C INTEGER STRBEG, STREND
C DIMENSION HX(10), IPERM(10)
C DATA (HX(I),I=1,10)/ '05','I ',' I',' ','Rs','9R','R9','89',
C 1 ',*','N"'/
C DATA STRBEG, STREND / 1, 2 /
C CALL HPSORT (HX,10,STRBEG,STREND,IPERM,1,W)
C PRINT 100, (HX(IPERM(I)),I=1,10)
C 100 FORMAT (2X, A2)
C STOP
C END
C
C***REFERENCES R. C. Singleton, Algorithm 347, An efficient algorithm
C for sorting with minimal storage, Communications of
C the ACM, 12, 3 (1969), pp. 185-187.
C***ROUTINES CALLED XERMSG
C***REVISION HISTORY (YYMMDD)
C 761101 DATE WRITTEN
C 761118 Modified by John A. Wisniewski to use the Singleton
C quicksort algorithm.
C 811001 Modified by Francis Sullivan for string data.
C 850326 Documentation slightly modified by D. Kahaner.
C 870423 Modified by Gregory S. Rhoads for passive sorting with the
C option for the rearrangement of the original data.
C 890620 Algorithm for rearranging the data vector corrected by R.
C Boisvert.
C 890622 Prologue upgraded to Version 4.0 style by D. Lozier.
C 920507 Modified by M. McClain to revise prologue text.
C 920818 Declarations section rebuilt and code restructured to use
C IF-THEN-ELSE-ENDIF. (SMR, WRB)
C***END PROLOGUE HPSORT
C .. Scalar Arguments ..
INTEGER IER, KFLAG, N, STRBEG, STREND
CHARACTER * (*) WORK
C .. Array Arguments ..
INTEGER IPERM(*)
CHARACTER * (*) HX(*)
C .. Local Scalars ..
REAL R
INTEGER I, IJ, INDX, INDX0, IR, ISTRT, J, K, KK, L, LM, LMT, M,
+ NN, NN2
C .. Local Arrays ..
INTEGER IL(21), IU(21)
C .. External Subroutines ..
EXTERNAL XERMSG
C .. Intrinsic Functions ..
INTRINSIC ABS, INT, LEN
C***FIRST EXECUTABLE STATEMENT HPSORT
IER = 0
NN = N
IF (NN .LT. 1) THEN
IER = 1
CALL XERMSG ('SLATEC', 'HPSORT',
+ 'The number of values to be sorted, N, is not positive.',
+ IER, 1)
RETURN
ENDIF
KK = ABS(KFLAG)
IF (KK.NE.1 .AND. KK.NE.2) THEN
IER = 2
CALL XERMSG ('SLATEC', 'HPSORT',
+ 'The sort control parameter, KFLAG, is not 2, 1, -1, or -2.',
+ IER, 1)
RETURN
ENDIF
C
IF(LEN(WORK) .LT. LEN(HX(1))) THEN
IER = 3
CALL XERMSG ('SLATEC',' HPSORT',
+ 'The length of the work variable, WORK, is too short.',
+ IER, 1)
RETURN
ENDIF
IF (STRBEG .GT. STREND) THEN
IER = 4
CALL XERMSG ('SLATEC', 'HPSORT',
+ 'The string beginning, STRBEG, is beyond its end, STREND.',
+ IER, 1)
RETURN
ENDIF
IF (STRBEG .LT. 1 .OR. STRBEG .GT. LEN(HX(1))) THEN
IER = 5
CALL XERMSG ('SLATEC', 'HPSORT',
+ 'The string beginning, STRBEG, is out-of-range.',
+ IER, 1)
RETURN
ENDIF
IF (STREND .LT. 1 .OR. STREND .GT. LEN(HX(1))) THEN
IER = 6
CALL XERMSG ('SLATEC', 'HPSORT',
+ 'The string end, STREND, is out-of-range.',
+ IER, 1)
RETURN
ENDIF
C
C Initialize permutation vector
C
DO 10 I=1,NN
IPERM(I) = I
10 CONTINUE
C
C Return if only one value is to be sorted
C
IF (NN .EQ. 1) RETURN
C
C Sort HX only
C
M = 1
I = 1
J = NN
R = .375E0
C
20 IF (I .EQ. J) GO TO 70
IF (R .LE. 0.5898437E0) THEN
R = R+3.90625E-2
ELSE
R = R-0.21875E0
ENDIF
C
30 K = I
C
C Select a central element of the array and save it in location L
C
IJ = I + INT((J-I)*R)
LM = IPERM(IJ)
C
C If first element of array is greater than LM, interchange with LM
C
IF (HX(IPERM(I))(STRBEG:STREND) .GT. HX(LM)(STRBEG:STREND)) THEN
IPERM(IJ) = IPERM(I)
IPERM(I) = LM
LM = IPERM(IJ)
ENDIF
L = J
C
C If last element of array is less than LM, interchange with LM
C
IF (HX(IPERM(J))(STRBEG:STREND) .LT. HX(LM)(STRBEG:STREND)) THEN
IPERM(IJ) = IPERM(J)
IPERM(J) = LM
LM = IPERM(IJ)
C
C If first element of array is greater than LM, interchange
C with LM
C
IF (HX(IPERM(I))(STRBEG:STREND) .GT. HX(LM)(STRBEG:STREND))
+ THEN
IPERM(IJ) = IPERM(I)
IPERM(I) = LM
LM = IPERM(IJ)
ENDIF
ENDIF
GO TO 50
40 LMT = IPERM(L)
IPERM(L) = IPERM(K)
IPERM(K) = LMT
C
C Find an element in the second half of the array which is smaller
C than LM
C
50 L = L-1
IF (HX(IPERM(L))(STRBEG:STREND) .GT. HX(LM)(STRBEG:STREND))
+ GO TO 50
C
C Find an element in the first half of the array which is greater
C than LM
C
60 K = K+1
IF (HX(IPERM(K))(STRBEG:STREND) .LT. HX(LM)(STRBEG:STREND))
+ GO TO 60
C
C Interchange these elements
C
IF (K .LE. L) GO TO 40
C
C Save upper and lower subscripts of the array yet to be sorted
C
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 80
C
C Begin again on another portion of the unsorted array
C
70 M = M-1
IF (M .EQ. 0) GO TO 110
I = IL(M)
J = IU(M)
C
80 IF (J-I .GE. 1) GO TO 30
IF (I .EQ. 1) GO TO 20
I = I-1
C
90 I = I+1
IF (I .EQ. J) GO TO 70
LM = IPERM(I+1)
IF (HX(IPERM(I))(STRBEG:STREND) .LE. HX(LM)(STRBEG:STREND))
+ GO TO 90
K = I
C
100 IPERM(K+1) = IPERM(K)
K = K-1
C
IF (HX(LM)(STRBEG:STREND) .LT. HX(IPERM(K))(STRBEG:STREND))
+ GO TO 100
IPERM(K+1) = LM
GO TO 90
C
C Clean up
C
110 IF (KFLAG .LE. -1) THEN
C
C Alter array to get reverse order, if necessary
C
NN2 = NN/2
DO 120 I=1,NN2
IR = NN-I+1
LM = IPERM(I)
IPERM(I) = IPERM(IR)
IPERM(IR) = LM
120 CONTINUE
ENDIF
C
C Rearrange the values of HX if desired
C
IF (KK .EQ. 2) THEN
C
C Use the IPERM vector as a flag.
C If IPERM(I) < 0, then the I-th value is in correct location
C
DO 140 ISTRT=1,NN
IF (IPERM(ISTRT) .GE. 0) THEN
INDX = ISTRT
INDX0 = INDX
WORK = HX(ISTRT)
130 IF (IPERM(INDX) .GT. 0) THEN
HX(INDX) = HX(IPERM(INDX))
INDX0 = INDX
IPERM(INDX) = -IPERM(INDX)
INDX = ABS(IPERM(INDX))
GO TO 130
ENDIF
HX(INDX0) = WORK
ENDIF
140 CONTINUE
C
C Revert the signs of the IPERM values
C
DO 150 I=1,NN
IPERM(I) = -IPERM(I)
150 CONTINUE
C
ENDIF
C
RETURN
END