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DOUBLE PRECISION FUNCTION ZABS(ZR, ZI)
C***BEGIN PROLOGUE ZABS
C***REFER TO ZBESH,ZBESI,ZBESJ,ZBESK,ZBESY,ZAIRY,ZBIRY
C
C ZABS COMPUTES THE ABSOLUTE VALUE OR MAGNITUDE OF A DOUBLE
C PRECISION COMPLEX VARIABLE CMPLX(ZR,ZI)
C
C***ROUTINES CALLED (NONE)
C***END PROLOGUE ZABS
DOUBLE PRECISION ZR, ZI, U, V, Q, S
U = DABS(ZR)
V = DABS(ZI)
S = U + V
C-----------------------------------------------------------------------
C S*1.0D0 MAKES AN UNNORMALIZED UNDERFLOW ON CDC MACHINES INTO A
C TRUE FLOATING ZERO
C-----------------------------------------------------------------------
S = S*1.0D+0
IF (S.EQ.0.0D+0) GO TO 20
IF (U.GT.V) GO TO 10
Q = U/V
ZABS = V*DSQRT(1.D+0+Q*Q)
RETURN
10 Q = V/U
ZABS = U*DSQRT(1.D+0+Q*Q)
RETURN
20 ZABS = 0.0D+0
RETURN
END
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