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27<center>
28EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH
29<IMG SRC="http://cern.ch/madx/icons/mx7_25.gif" align=right>
30<h2> Rules for Fortran routines for MAD-X</B></h2> 
31</center>
32
33<UL>
34<LI><B> Code</B>
35 
36<OL>
37<LI>lower case throughout</LI>
38<LI>all routines start with ``implicit none''</LI>
39<LI>the following types should be used exclusively:
40 
41<UL>
42<LI>integer - use integer as well instead of logical, 0 = false,
43         else true</LI>
44<LI>double precision (not real*8)</LI>
45<LI>complex*16 - only internally, and in cases where it really helps</LI>
46<LI>character - if this routine can be called from outside
47     (i.e. as well from C routines), always foresee a length input
48     variable (see example). When calling a C routine with character strings,
49     make sure they end with a blank (e.g. 'abc ').
50  </LI>
51</UL></LI>
52<LI>use only generic names for functions, i.e. sin, cos, abs, exp
53    etc. and <B> not</B> dsin, dcos, dabs, dexp etc.; nota bene: ANSI
54    for arcus sinus and arcus cosinus is asin and acos (not arsin and arcos)
55 </LI>
56<LI>do not use statement functions, arithmetic IF (3-branch), or IMPLICIT GOTO.
57 </LI>
58<LI>in DO loops: use always do...enddo constructs.
59 </LI>
60<LI>IMPORTANT: when transferring  strings to C routines, always terminate
61    the string with a blank, e.g.
62<PRE>
63      call double_to_table('twiss ', 'betx ', betx)
64</PRE>
65 </LI>
66<LI>When transferring  integer or double to C routines, always use
67    specific variables (no values or expressions), e.g. to receive the
68    current element name
69<PRE>
70      integer i
71      character * 16 name
72      i = 16
73      call element_name(name, i)
74</PRE>
75 </LI>
76</OL></LI>
77<LI><B> Style</B>
78 
79<OL>
80<LI>all modules and stand-alone routines perform all input/output
81        through symbolic variables in the call (no ``common'');
82        common blocks can be used inside modules, however.</LI>
83<LI>functions return only one (the function-) value and do not
84        modify any of the input variables</LI>
85<LI>all input/output parameters are described, and the routine
86    purpose stated</LI>
87<LI>avoid ``goto'' as far as reasonable</LI>
88<LI>indent do ... enddo and if ... then ... else constructs</LI>
89<LI>avoid using ``return'';
90        only one exit of the routine, at the end (this makes
91        debugging easier)
92 </LI>
93<LI>no I/O (read, write, print to files) in a Fortran routine, except
94        for printing to output (error messages, summary data etc.);
95        most of the data will be put into tables via C routine calls.</LI>
96<LI>    Error flags, or calls to special exception routines
97        can be foreseen as need arises.</LI>
98</OL></LI>
99<LI><B> General</B>
100 
101<OL>
102<LI>for local buffers of moderate size use local arrays; for bulk
103        storage use blank common; blank common may as well be used to
104        pass data inside modules</LI>
105<LI>for matrix manipulation use the existing m66 package</LI>
106<LI>do not use any external library (e.g. cernlib), rather extract
107        and include the code needed
108 </LI>
109</OL></LI>
110<LI><B> Checks are essential!!</B>
111<OL>
112<LI> Run your code through f2c to check that the Fortran is compatible
113with standard Fortran 77. Recent testing of the MAD-X Fortran77 code has
114revealed some problematic programming techniques.
115Example: f2c twiss.F
116<LI> Use the NAG f95 compiler with very strict checking by using
117"make -f Makefile_develop (madxp)" in brackets if you test the MAD-X
118        PTC version.</LI>
119<LI> Then run your example with that executable. The "-nan" compile
120        flags will demonstrate at run time if variables have not been
121properly initialized so as to allow for fixing this problem.
122 </LI>
123<LI> At last the MAD-X custodian (presently FS) will check the
124        compatibility with Fortran90. Thereby performing certain
125        "beautification" procedures. Moreover, the NAG f95 compiler
126        reveals more inconsistencies in the Fortran90 mode.
127 </LI>
128</OL></LI>
129</UL>
130 
131<B> Example</B>
132<PRE>
133
134      integer function type(s_length, s_type)
135*++ Purpose: returns an integer type code for certain elements
136*-- input:
137*   s_length   length of s_type
138*   s_type     string containing type
139*-- return values:
140*   1   for s_type == 'drift'
141*   2   for s_type == 'sbend'
142*   3   for s_type == 'rbend'
143*   5   for s-type == 'quadrupole'
144*   0   else
145*++
146      implicit none
147      integer s_length
148      character *(*) s_type
149
150      if (s_type(:s_length) .eq. 'drift')  then
151        type = 1
152      elseif (s_type(:s_length) .eq. 'sbend')  then
153        type = 2
154      elseif (s_type(:s_length) .eq. 'rbend')  then
155        type = 3
156      elseif (s_type(:s_length) .eq. 'quadrupole')  then
157        type = 5
158      else
159        type = 0
160      endif
161      end
162</PRE>
163<BR><HR>
164<aDDRESS>
165<I>Hans Grote</I>
166<BR><I>2001-01-22</I>
167</ADDRESS>
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