It depends upon what is in the table or how a set of nested
if-then-else statements were written.
Such code is easy to replace. Consider
mdlfind: procedure(MDLTABp, cyls)
returns(character(6) varying)
reorder ;
/* uses lub-seeking binary search to find the subscript i of the
element MDLTAB.tab.ncyl(i) for which MDLTAB.tab.ncyl >= cyls
is a minimum, i.e.,
min(i | MDLTAB.tab.ncyl >= cyls)
If such a lub is found the return code is set to 0 and the nickname
of the corresponding pseudo-3390 model is returned as the value
of this function. If instead no lub is found the return code is set to
1 and a null string is returned as the value of this function.
*/
/* parameters */
declare (MDLTABp /* -> MDLTAB */
pointer,
cyls /* cylinders */
binary fixed(31,0))
nonassignable ;
/* table template */
declare 1 MDLTAB based(MDLTABp),
2 eye character(8) /* eyecatcher: 'MDLTAB ' */
2 nmd /* number of models */
signed binary fixed(31,0),
2 tab(1 refer(MDLTAB.nmd),
3 ncyl /* number of cylinders */
signed binary fixed(31,0),
3 nick /* nickname */
character(6) varying ;
/* LIFO scratch storage */
declare (lo, mi, hi, retcode)
signed binary fixed(31,0) ;
declare (again, bounded, search_higher)
aligned bit ;
declare nickout character(6) varying ;
/* named constants, BIF used */
declare (F0 initial(0b), F1 initial(1b), F2 initial(10b))
signed binary fixed(31,0) ;
declare pliretc builtin ;
lo = F1 ;
hi = MDLTAB.nmd ;
do again = (lo <= hi) repeat(lo <= hi) while(again) ;
mi = lo + (hi - lo)/F2 ;
search_higher = (cyls < MDLTAB.tab.ncyl) ;
if search_higher then lo = mi + F1 ;
else hi = mi - F1 ;
end ;
bounded = (hi <= MDLTAB.nmd) ;
if bounded then
do ;
retcode = F0 ;
nickout = MDLTAB.tab.nick(hi) ;
end ;
else
do ;
retcode = F1 ;
nickout = '' ;
end ;
call pliretc(retcode) ;
return ;
end mdlfind ;
This is PL/I, but it could serve as a template for another
implementation. One in assembly language would be easy; one in C
would be possible.
The merits of such an approach are that it consistently produces a
least upper bound on a cylinders value and is easily changed/extended
by changing only the external table it uses.
John Gilmore, Ashland, MA 01721 - USA
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