GNU Octave  3.8.0 A high-level interpreted language, primarily intended for numerical computations, mostly compatible with Matlab
zs1s2.f
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1  SUBROUTINE zs1s2(ZRR, ZRI, S1R, S1I, S2R, S2I, NZ, ASCLE, ALIM,
2  * iuf)
3 C***BEGIN PROLOGUE ZS1S2
4 C***REFER TO ZBESK,ZAIRY
5 C
6 C ZS1S2 TESTS FOR A POSSIBLE UNDERFLOW RESULTING FROM THE
7 C ADDITION OF THE I AND K FUNCTIONS IN THE ANALYTIC CON-
8 C TINUATION FORMULA WHERE S1=K FUNCTION AND S2=I FUNCTION.
9 C ON KODE=1 THE I AND K FUNCTIONS ARE DIFFERENT ORDERS OF
10 C MAGNITUDE, BUT FOR KODE=2 THEY CAN BE OF THE SAME ORDER
11 C OF MAGNITUDE AND THE MAXIMUM MUST BE AT LEAST ONE
12 C PRECISION ABOVE THE UNDERFLOW LIMIT.
13 C
14 C***ROUTINES CALLED XZABS,XZEXP,XZLOG
15 C***END PROLOGUE ZS1S2
16 C COMPLEX CZERO,C1,S1,S1D,S2,ZR
17  DOUBLE PRECISION aa, alim, aln, ascle, as1, as2, c1i, c1r, s1di,
18  * s1dr, s1i, s1r, s2i, s2r, zeroi, zeror, zri, zrr, xzabs
19  INTEGER iuf, idum, nz
20  DATA zeror,zeroi / 0.0d0 , 0.0d0 /
21  nz = 0
22  as1 = xzabs(s1r,s1i)
23  as2 = xzabs(s2r,s2i)
24  IF (s1r.EQ.0.0d0 .AND. s1i.EQ.0.0d0) go to 10
25  IF (as1.EQ.0.0d0) go to 10
26  aln = -zrr - zrr + dlog(as1)
27  s1dr = s1r
28  s1di = s1i
29  s1r = zeror
30  s1i = zeroi
31  as1 = zeror
32  IF (aln.LT.(-alim)) go to 10
33  CALL xzlog(s1dr, s1di, c1r, c1i, idum)
34  c1r = c1r - zrr - zrr
35  c1i = c1i - zri - zri
36  CALL xzexp(c1r, c1i, s1r, s1i)
37  as1 = xzabs(s1r,s1i)
38  iuf = iuf + 1
39  10 CONTINUE
40  aa = dmax1(as1,as2)
41  IF (aa.GT.ascle) RETURN
42  s1r = zeror
43  s1i = zeroi
44  s2r = zeror
45  s2i = zeroi
46  nz = 1
47  iuf = 0
48  RETURN
49  END