SUBROUTINE SROTMGF (SD1,SD2,SX1,SY1,SPARAM)

C

C     CONSTRUCT THE MODIFIED GIVENS TRANSFORMATION MATRIX H WHICH ZEROS

C     THE SECOND COMPONENT OF THE 2-VECTOR  (SQRT(SD1)*SX1,SQRT(SD2)*

C     SY2)**T.

C     WITH SPARAM(1)=SFLAG, H HAS ONE OF THE FOLLOWING FORMS..

C

C     SFLAG=-1.E0     SFLAG=0.E0        SFLAG=1.E0     SFLAG=-2.E0

C

C       (SH11  SH12)    (1.E0  SH12)    (SH11  1.E0)    (1.E0  0.E0)

C     H=(          )    (          )    (          )    (          )

C       (SH21  SH22),   (SH21  1.E0),   (-1.E0 SH22),   (0.E0  1.E0).

C     LOCATIONS 2-4 OF SPARAM CONTAIN SH11,SH21,SH12, AND SH22

C     RESPECTIVELY. (VALUES OF 1.E0, -1.E0, OR 0.E0 IMPLIED BY THE

C     VALUE OF SPARAM(1) ARE NOT STORED IN SPARAM.)

C

C     THE VALUES OF GAMSQ AND RGAMSQ SET IN THE DATA STATEMENT MAY BE

C     INEXACT.  THIS IS OK AS THEY ARE ONLY USED FOR TESTING THE SIZE

C     OF SD1 AND SD2.  ALL ACTUAL SCALING OF DATA IS DONE USING GAM.

C

      DIMENSION SPARAM(5)

C

      DATA ZERO,ONE,TWO /0.E0,1.E0,2.E0/

      DATA GAM,GAMSQ,RGAMSQ/4096.E0,1.67772E7,5.96046E-8/

      IF(.NOT. SD1 .LT. ZERO) GO TO 10

C       GO ZERO-H-D-AND-SX1..

          GO TO 60

   10 CONTINUE

C     CASE-SD1-NONNEGATIVE

      SP2=SD2*SY1

      IF(.NOT. SP2 .EQ. ZERO) GO TO 20

          SFLAG=-TWO

          GO TO 260

C     REGULAR-CASE..

   20 CONTINUE

      SP1=SD1*SX1

      SQ2=SP2*SY1

      SQ1=SP1*SX1

C

      IF(.NOT. ABS(SQ1) .GT. ABS(SQ2)) GO TO 40

          SH21=-SY1/SX1

          SH12=SP2/SP1

C

          SU=ONE-SH12*SH21

C

          IF(.NOT. SU .LE. ZERO) GO TO 30

C         GO ZERO-H-D-AND-SX1..

               GO TO 60

   30     CONTINUE

               SFLAG=ZERO

               SD1=SD1/SU

               SD2=SD2/SU

               SX1=SX1*SU

C         GO SCALE-CHECK..

               GO TO 100

   40 CONTINUE

          IF(.NOT. SQ2 .LT. ZERO) GO TO 50

C         GO ZERO-H-D-AND-SX1..

               GO TO 60

   50     CONTINUE

               SFLAG=ONE

               SH11=SP1/SP2

               SH22=SX1/SY1

               SU=ONE+SH11*SH22

               STEMP=SD2/SU

               SD2=SD1/SU

               SD1=STEMP

               SX1=SY1*SU

C         GO SCALE-CHECK

               GO TO 100

C     PROCEDURE..ZERO-H-D-AND-SX1..

   60 CONTINUE

          SFLAG=-ONE

          SH11=ZERO

          SH12=ZERO

          SH21=ZERO

          SH22=ZERO

C

          SD1=ZERO

          SD2=ZERO

          SX1=ZERO

C         RETURN..

          GO TO 220

C     PROCEDURE..FIX-H..

   70 CONTINUE

      IF(.NOT. SFLAG .GE. ZERO) GO TO 90

C

          IF(.NOT. SFLAG .EQ. ZERO) GO TO 80

          SH11=ONE

          SH22=ONE

          SFLAG=-ONE

          GO TO 90

   80     CONTINUE

          SH21=-ONE

          SH12=ONE

          SFLAG=-ONE

   90 CONTINUE

      GO TO IGO,(120,150,180,210)

C     PROCEDURE..SCALE-CHECK

  100 CONTINUE

  110     CONTINUE

          IF(.NOT. SD1 .LE. RGAMSQ) GO TO 130

               IF(SD1 .EQ. ZERO) GO TO 160

               ASSIGN 120 TO IGO

C              FIX-H..

               GO TO 70

  120          CONTINUE

               SD1=SD1*GAM**2

               SX1=SX1/GAM

               SH11=SH11/GAM

               SH12=SH12/GAM

          GO TO 110

  130 CONTINUE

  140     CONTINUE

          IF(.NOT. SD1 .GE. GAMSQ) GO TO 160

               ASSIGN 150 TO IGO

C              FIX-H..

               GO TO 70

  150          CONTINUE

               SD1=SD1/GAM**2

               SX1=SX1*GAM

               SH11=SH11*GAM

               SH12=SH12*GAM

          GO TO 140

  160 CONTINUE

  170     CONTINUE

          IF(.NOT. ABS(SD2) .LE. RGAMSQ) GO TO 190

               IF(SD2 .EQ. ZERO) GO TO 220

               ASSIGN 180 TO IGO

C              FIX-H..

               GO TO 70

  180          CONTINUE

               SD2=SD2*GAM**2

               SH21=SH21/GAM

               SH22=SH22/GAM

          GO TO 170

  190 CONTINUE

  200     CONTINUE

          IF(.NOT. ABS(SD2) .GE. GAMSQ) GO TO 220

               ASSIGN 210 TO IGO

C              FIX-H..

               GO TO 70

  210          CONTINUE

               SD2=SD2/GAM**2

               SH21=SH21*GAM

               SH22=SH22*GAM

          GO TO 200

  220 CONTINUE

          IF(SFLAG)250,230,240

  230     CONTINUE

               SPARAM(3)=SH21

               SPARAM(4)=SH12

               GO TO 260

  240     CONTINUE

               SPARAM(2)=SH11

               SPARAM(5)=SH22

               GO TO 260

  250     CONTINUE

               SPARAM(2)=SH11

               SPARAM(3)=SH21

               SPARAM(4)=SH12

               SPARAM(5)=SH22

  260 CONTINUE

          SPARAM(1)=SFLAG

          RETURN

      END