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                 DEC20/VAX CONVERSION ITEMS

     1.  Accuracy

     2.  Character data

     3.  Logical bit manipulation

     4.  Open statement

     5.  Random number generator

                 DEC20/IBM CONVERSION ITEMS

     1.  Accuracy

     2.  Character data

     3.  Logical bit manipulation

     4.  Open statement

     5.  Random number generator

     6.  ASCII/EBCDIC conversion ("tab" char.  problem)

     7.  Free-field formatting

     8.  Hexidecimal constants

     9.  Carriage control


    11.  Encode/Decode

    12.  Format literals

    13.  "Tab" in col.  1



     This  is  a  list  of  the  Fortran  conversion   items
encountered during the Monte Carlo program conversion.

     The  items  are  rated  in  severity  of  impact  on  a
conversion,  with  5  being  the most severe, down to 0 (for
probably no effect).   In  addition,  for  the  two  fortran
classes,  an  estimate  has  been  made of the percentage of
existing Fortran programs that are affected.


Accuracy (36 bit to 32 bit)             5*              5*              100

5 char/word to 4 char/word              4               4               100

Logical bit manipulation                4               4               10

Free field formatting                   2               4               80

Random Number Generation                1               1               5

Character mode (ASCII to EBCDIC)        0               2               25
        ("tab" char. problem)

Hex and octal constants                 1               2               25

Cursor/screen control                   0               5               50

File specifications in OPEN st.         1               1               95

Instruction line comments               0               1               20

ENCODE/DECODE                           0               1               60

Continued literal in format st.         0               1               10

"tab" in col. 1 of statement            0               1               100


     Verifying and accepting changes in output accuracy  due
to  the  different word length would be a length task in any
event.  IN ADDITION to this, there are programs (such as EPA
certification)  for  which the results obtained from the new
system must  EXACTLY  match  the  previous  results.   These
programs  will be a special problem;  a 32 bit fullword will
give minor (but  in  this  case  important)  differences  in
computational   accuracy,   and   even  changing  to  double
precision may not eliminate this.   (Double  precision  will
hold  MORE  accuracy than the original 36 bit word, and this
would STILL introduce differences into the converted program


The  following    have been identifi  major  conversion 
considerations.  This list c conversion considerations; 
issues  such  as  computer  po  res  time,  and  f 
applications development have not been included.

Description                           Effort Involved    Freq. of
                                   DEC20 to   DEC20 to  Occurance
                                      VAX        IBM

------- ---------- -----

1. Synamic filename specification       0         5*        25

2. Data Base handling                   1         4         85

3. Graphics                             ?         ?         20

4. Cursor control                       2         ?         ?

5. Baseline Fortran program             2**       3**       15
   (not using 1-4) -- conversion
   of the Monte Carlo program

                              ** overall "average" of time and
                                 effort spend on Monte Carlo

----- -----

1. System level command files           2         4         100

2. Batch control files                  2         4         100

3. Data base control files              1         5         100

4. Rebuild data bases                   1         3         100

5. Rebuild screen interfaces            1         5**       100

6. Special software (Versatec,          ?         ?         100
   Zeta, Nyplan, Plot79, PacII)
   -- Availability
   -- Data conversion

7. MACRO                                5         5         100

8. BASIC                                2         3         100

     * Indicates that no comparable facility exists.  Conversion
       would require extensive recoding or multiple custom
       coding to simuate this capability.



0 ---     No conversion necessary.

1 ----    can be performed by a search/replace without any
          additional checking.

2 -----   changes that must be checked with a global search to
          confirm that the change will no cause problems.

          Single statement changes that require completely
          reworking a statement.

          Changes that require fixed data format changes.

3 -----   Changes that require tracing parameter(s) values
          through the program.

          Changes that require SLIGHT learning of meaning of
          existing code.

4 -----   Changes require replacing groups of statements where
          the new group is a simple replacement of the old one.

          Variable data format changes.

          Changes requiring SOME learning of meaning of
          existing code.

5 -----   Major changes:

          Those requiring EXTENSIVE learning of meaning of
          original code.

          Accuracy verification.  This is a major conversion,
          even though it is not a code "change."

NOTE:     This  scale reflects both the difficulty and  the  time 
neces to   a  s change  of  the  ty   described.   Howe multiple occurrences of a  change   inc for that  change 
 repl  every tab in  1 with the  co   nu of  spaces).   On this conver  there  w several  "simple"  changes  of  this  type    too    appreciable time to make.


                      EFFORT SCALE FOR "OTHER AREAS"

1 -----   No conversion necessary

2 -----   changes that can be made without checking for upstream
          or downstream considerations of effects.

2 -----   changes that require "routine" checking (such as a
          global search) to insure there are no prior or 
          subsequent effects.

          Changes that require rewriting old code, but on a 
          line-for-line replacement basis that would not require
          knowledge of the meaning of the old code.

3 -----   changes that would require tracing parameters or 
          control parameter values through a control file to
          insure correct operation.

          cha would require SLIGHT lea of  meaning
          of existing code.

4 -----   Changes requiring replacing groups of statements 
          where  th group is a simple replac of the old
          one, but without a no-to one correspondence between
          individual lines.  The converted code retains the
          "structure" of the old code.

          Changes requiring SOME learning of meaning of 
          existing code.

5 -----   Changes requiring extensive rewriting of code resulting
          in new code that is structurally different from the old

          Changes requiring EXTENSIVE learning of the meaning
          of the old code.


                DEC20/VAX & DEC20/IBM COMPARISON

     Monte  Carlo program was converted fro 20  to 
both the VAX 75 the IBM 4331/VM to obtain an estimate o 
ef needed  to convert a "benchmark" progra a  differ
system.   Having  the same pr conv to both the VAX  and 
IBM also provided some data about the time difference be the 
two conversions.

    need convert the DEC20 program to the IBM 4331 
was about 1./3 to 1.4 times that needed to convert to the VAX.
     Two  important    mus  about  this  estimate.  
Fi ther no vital cursor or screen control/forma
the  Carlo pro  therefor question of terminal typ  con not figur  eff  Sec two 
conversions were not ma a to separate basis  first 
conve DEc20 program to the VAX;  the req 
later  to co it DEC20 to IBM.   I rea of   had been done on the DEC20/VAX conversion was necessary 
for the DEC20/IBM conversion (in particular,  the shift from a 36   ful byte-oriented 32 bit fullword).   I  therefore 
started  the  IBM  conver usin  converted  pr 
in of starting again o DEC20 ver and kept 
any "VAX dependent :  work that had to be undone  to the IBm 
version.  As it turned out,  there was very little that had to be 

     This   "consecutive"  effort  was  reflected  in  the   t
esti two conversions.   The  VAX  conve  time 
included  only  the time n for the VAX ch to the  code.  
Th conversion inc the VAX conversion time AND   need convert the VAX version to the IBM.

                    DEC 20 to VAX CONVERSION

     The  biggest  e  in this conve  shi 
"alphanumeric"  variables and arrays from a 5-character/word    configur 4 characters/word (byte oriented 32  bit 
fullword)   use by the VAX.   Shifting some parameters  from 
single  preci to d prec of part  of  the 
problem, but many arrays had to be redimensioned to kee 
allowable  s length.   Similarly,  format editing paramet
had to be redone to match the shifted arrays.

     Two   programming techniques that had been us 
original  pr required  over  For
"character"  data was ca in both real and in  variables 
(  no  way of handling it).   The VAX For 77, 
which  includes th character/string  manipulation  features, 
severely  restr the manipulation and output of character data in a rea 
in vari  Solving this  rewr lines (and at  sect


     The second programming technique that required restructuring 
was lo bit manipulati an assignment state the 
DEC20,  the  assig stat A=B.OR.C is legal with logical, 
  int parameters.    On  the   howe 
parameters  are  not  allow  Furtherm crea inte
parameters  set  equal t need  operation 
would not work; the conversion in executing the instruction would 
destroy the original bit pat   Backup and reworking code  to 
  onl allo types whe logical  assig 
statements were executed had to be done.

     A   format fe figured i conversion  even 
thoug was not troubl AT THIS T  DEC20 Fo 
free  f and "I" format  exa  for
stat  FORMAT(7F)  will allow the correct edi of  up  to 
seven real quant located anywhe the record,  as long as 
there  i leas space between adjacent fields.   The  VAX 
Fortran  does not formally support this free  capabilit 
even me it, so far as I could find).  While experimenting
found tha field formatting would work o VAX if the 
f  were  seperate by commas instead of (o addi to) 
spa  Therefore, with the changed data syntax, the free field 
forma  still functio VAX Fortran,  but since  
formally  supported,  DEC  has no obligati  pre
future editions of VAX Fortran.

     Other  ch  were  necessary,  but    were  "normal" 
conver items,  such  as  different r  number  generator 
syntax and different OPEN statement syntax.

                 DEC20 to IBM 4331/VM CONVERSION

     As  I noted be  I started this conversion with the  VAX 
c rather than the DEC20 code.  The only VAX fe had 
to be "b was the new OPEN statement sy the changes 
neede  DEC20/VAX shift were entirely  replace 
needed IBM changes.  This was the only identifiable "lost" eff
from the VAX converted code.

     Mo the source cod files over to the 4331  
converting them to EBCDI a major proble did not include 
this   as part of my Fortran  conver  how  even  a 
smoothly-running  transfer from one ma to another would need 
some time per program to be performed.  i could not est 
at this time.
     Se  conversion items were found  changing the   to IBM.   The foremost of these was that free-field "I"  and 
"F" ed is not supported,  either for or inform  To 
convert the code, all I/O using this featur shifted to list-
directed  I/O,  a now-standard fortran feature.   The only way to 
make  this  work w a fu chan  entry 
syntax;  in  additio the comma-separation use 
version,  any "character" f on the data input r
enclosed in qu the  record mu terminated by a 


     Ano far less major, conversion item was specifying 
a  hexadec cons in an assignment  statem  Thi 
al DEC2 VAX Fortran, but not on IBM VS For
Fortran  allows  hex  constants  only    dat  parameter 
statem  I  conve the progr  specifying  e hex 
constant used in the program in DATA statement.

     Se  other  "normal"  conversion   were  found  
converted.   One  that was found that could not be converted  was 
specif a fi "readonly" in the Fortran source c  On  4331,  this could only be done in the FILEDEF or JCL, and not 
at the source level.


     During th conversion eff  I kept track of the time 
actually sp included actual code  convers research   learning,  and  dead ends.   After each conversion,  I  also 
estim the time that  be necessary to convert a  si 
program using the lessons gained while doing the first one.

     On the basis of actual time s IBM conve  took 
40%  l  tha VAX conversion.   The IBM conversion   time 
inc  DEC20/VA VAX/IBM conversion   minus  the 
time spend "undoing" the unnecessary VAX changes.

   basis of post-learning curve   I estimate  t IBM conve would be reduc abou  that 
the VAX.


                     VAX/IBM 4331 COMPARISON

DEC20 to VAX                      DEC20 to IBM
------------                      ------------

Accuracy considerations in shift  Same
from 36 bit to 32 bit fullword.

Changing from 5 char/word to      Same
4 char/word for character strings

Logical bit manipulation cannot   Same
be done on real parameters.

Free field "F" and "I" editing:   Free-field "F" and "I" not
a) It is not FORMALLY             supported.  (list-directed
   support on VAX.  However, it   I/O replaced them in this
   works on the edition of the    conversion; this required
   compiler.                      input data syntax changes.)
b) Data fields must be separated
   by commas (not just spaces).

Different random number           Same
generator and syntax

Character mode conversion not     ASCII/EBCDIC conversion must
needed to move files from DEC20   be done to move files from
to VAX.                           DEC20 to IBM.

Hex and Octal constants allowed   Hex constants not allowed in
in assignment statements (same    assignment statement (only in
as DEC20)                         DATA & PARAMETER statements).

"+" and "$" carriage control      "+" and "$" carriage control
suppression allowed (same as      suppression not allowed.

Changes needed to OPEN statement: Changes needed to OPEN statement:
a  option             diff disposition parameter
b) different ACCESS entry         b) "." in file name not allowed
c) no DEVICE option                  (ex: gpc970.DAT)
d) different method of specifying c) No method of specifying
   read-only file                    read-only  in the OPEN

Comments allowed on an            No allowed in IBM VS Fortran
instruction line following "!"
(same as DEC20)

ENCODE and DECODE supported as    ENCODE and DECODE not supported.
extensions to standard FORTRAN    (can be replaced by internal read/


Trailing blanks in a format       Handled differently on IBM--
literal that is continued on      must be converted to yield the
another line. handled same as     same output.

A "tab" in pos. 1 of an intitial  A "tab" in pos. 1 is not allowed
or continuation line is allowed   (VS Fortran has free-form option,
(same as DEC20)                   but this particular item is not
                                  supported in it.)