amos/zabs.f

   1       DOUBLE PRECISION FUNCTION AZABS(ZR, ZI)
   2 C***BEGIN PROLOGUE  AZABS
   3 C***REFER TO  ZBESH,ZBESI,ZBESJ,ZBESK,ZBESY,ZAIRY,ZBIRY
   4 C
   5 C     AZABS COMPUTES THE ABSOLUTE VALUE OR MAGNITUDE OF A DOUBLE
   6 C     PRECISION COMPLEX VARIABLE CMPLX(ZR,ZI)
   7 C
   8 C***ROUTINES CALLED  (NONE)
   9 C***END PROLOGUE  AZABS
  10       DOUBLE PRECISION ZR, ZI, U, V, Q, S
  11       U = DABS(ZR)
  12       V = DABS(ZI)
  13       S = U + V
  14 C-----------------------------------------------------------------------
  15 C     S*1.0D0 MAKES AN UNNORMALIZED UNDERFLOW ON CDC MACHINES INTO A
  16 C     TRUE FLOATING ZERO
  17 C-----------------------------------------------------------------------
  18       S = S*1.0D+0
  19       IF (S.EQ.0.0D+0) GO TO 20
  20       IF (U.GT.V) GO TO 10
  21       Q = U/V
  22       AZABS = V*DSQRT(1.D+0+Q*Q)
  23       RETURN
  24    10 Q = V/U
  25       AZABS = U*DSQRT(1.D+0+Q*Q)
  26       RETURN
  27    20 AZABS = 0.0D+0
  28       RETURN
  29       END