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85 lines
2.6 KiB
Fortran
85 lines
2.6 KiB
Fortran
*DECK DXRED
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SUBROUTINE DXRED (X, IX, IERROR)
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C***BEGIN PROLOGUE DXRED
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C***PURPOSE To provide double-precision floating-point arithmetic
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C with an extended exponent range.
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C***LIBRARY SLATEC
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C***CATEGORY A3D
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C***TYPE DOUBLE PRECISION (XRED-S, DXRED-D)
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C***KEYWORDS EXTENDED-RANGE DOUBLE-PRECISION ARITHMETIC
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C***AUTHOR Lozier, Daniel W., (National Bureau of Standards)
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C Smith, John M., (NBS and George Mason University)
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C***DESCRIPTION
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C DOUBLE PRECISION X
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C INTEGER IX
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C
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C IF
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C RADIX**(-2L) .LE. (ABS(X),IX) .LE. RADIX**(2L)
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C THEN DXRED TRANSFORMS (X,IX) SO THAT IX=0.
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C IF (X,IX) IS OUTSIDE THE ABOVE RANGE,
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C THEN DXRED TAKES NO ACTION.
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C THIS SUBROUTINE IS USEFUL IF THE
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C RESULTS OF EXTENDED-RANGE CALCULATIONS
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C ARE TO BE USED IN SUBSEQUENT ORDINARY
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C DOUBLE-PRECISION CALCULATIONS.
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C
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C***SEE ALSO DXSET
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C***REFERENCES (NONE)
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C***ROUTINES CALLED (NONE)
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C***COMMON BLOCKS DXBLK2
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C***REVISION HISTORY (YYMMDD)
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C 820712 DATE WRITTEN
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C 881020 Revised to meet SLATEC CML recommendations. (DWL and JMS)
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C 901019 Revisions to prologue. (DWL and WRB)
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C 901106 Changed all specific intrinsics to generic. (WRB)
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C Corrected order of sections in prologue and added TYPE
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C section. (WRB)
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C 920127 Revised PURPOSE section of prologue. (DWL)
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C***END PROLOGUE DXRED
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DOUBLE PRECISION X
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INTEGER IX
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DOUBLE PRECISION RADIX, RADIXL, RAD2L, DLG10R, XA
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INTEGER L, L2, KMAX
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COMMON /DXBLK2/ RADIX, RADIXL, RAD2L, DLG10R, L, L2, KMAX
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SAVE /DXBLK2/
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C
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C***FIRST EXECUTABLE STATEMENT DXRED
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IERROR=0
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IF (X.EQ.0.0D0) GO TO 90
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XA = ABS(X)
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IF (IX.EQ.0) GO TO 70
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IXA = ABS(IX)
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IXA1 = IXA/L2
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IXA2 = MOD(IXA,L2)
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IF (IX.GT.0) GO TO 40
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10 CONTINUE
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IF (XA.GT.1.0D0) GO TO 20
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XA = XA*RAD2L
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IXA1 = IXA1 + 1
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GO TO 10
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20 XA = XA/RADIX**IXA2
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IF (IXA1.EQ.0) GO TO 70
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DO 30 I=1,IXA1
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IF (XA.LT.1.0D0) GO TO 100
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XA = XA/RAD2L
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30 CONTINUE
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GO TO 70
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C
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40 CONTINUE
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IF (XA.LT.1.0D0) GO TO 50
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XA = XA/RAD2L
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IXA1 = IXA1 + 1
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GO TO 40
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50 XA = XA*RADIX**IXA2
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IF (IXA1.EQ.0) GO TO 70
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DO 60 I=1,IXA1
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IF (XA.GT.1.0D0) GO TO 100
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XA = XA*RAD2L
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60 CONTINUE
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70 IF (XA.GT.RAD2L) GO TO 100
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IF (XA.GT.1.0D0) GO TO 80
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IF (RAD2L*XA.LT.1.0D0) GO TO 100
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80 X = SIGN(XA,X)
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90 IX = 0
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100 RETURN
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END
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