xzabs.f

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      DOUBLE PRECISION FUNCTION xzabs(ZR, ZI)
C***BEGIN PROLOGUE  XZABS
C***REFER TO  ZBESH,ZBESI,ZBESJ,ZBESK,ZBESY,ZAIRY,ZBIRY
C
C     XZABS COMPUTES THE ABSOLUTE VALUE OR MAGNITUDE OF A DOUBLE
C     PRECISION COMPLEX VARIABLE CMPLX(ZR,ZI)
C
C***ROUTINES CALLED  (NONE)
C***END PROLOGUE  XZABS
      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
      xzabs = v*dsqrt(1.d+0+q*q)
      RETURN
   10 q = v/u
      xzabs = u*dsqrt(1.d+0+q*q)
      RETURN
   20 xzabs = 0.0d+0
      RETURN
      END