pythag.f

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      DOUBLE PRECISION FUNCTION pythag(A,B)
      DOUBLE PRECISION a,b
C
C     FINDS DSQRT(A**2+B**2) WITHOUT OVERFLOW OR DESTRUCTIVE UNDERFLOW
C
      DOUBLE PRECISION p,r,s,t,u
      p = dmax1(dabs(a),dabs(b))
      IF (p .EQ. 0.0d0) goto 110
      r = (dmin1(dabs(a),dabs(b))/p)**2
  100 CONTINUE
         t = 4.0d0 + r
         IF (t .EQ. 4.0d0) goto 110
         s = r/t
         u = 1.0d0 + 2.0d0*s
         p = u*p
         r = (s/u)**2 * r
      goto 100
  110 pythag = p
      RETURN
      END