====== Vroom=====

^Published By^Date^Version^Knowledge Level^Keywords^
|Sprezzatura Ltd|01 APR 1990|1.16+|EXPERT|VROOM, INDEX, SELECT, BASIC, PERFORM, SPEED, FIELD|

As promised, the first in an occasional series with hints on getting the
most from Advanced Revelation. Whilst it is generally more cost effective to
put in faster hardware than spend weeks optimising software, an awareness of
possible improvements is still useful. Some of the hints included here may
seem obvious, but all are taken from hints delivered to experienced REV/AREV
programmers recently.

==== Testing For a Value ====

It is frequently necessary when eliciting user response to ensure that the
information returned is valid.  This can be done in the following manner
(the code is by way of example only, obviously it can be improved in other
ways, popups, collectors, @LOWER.CASE etc).

<code>
    VALID = 0
    ANS = ""
    LOOP
       CALL MSG("Y/N","RC",ANS,"")
       IF ANS="Y" OR ANS="y" OR ANS="N" OR ANS="n" THEN
          VALID = 1
       END
    UNTIL VALID
    REPEAT
</code>

however, it can be accomplished more efficiently with the construct

<code>
    VALID = 0
    ANS = ""
    LOOP
       CALL MSG("Y/N","R",ANS,"")
       IF INDEX("YyNn",ANS,1) THEN VALID = 1
    UNTIL VALID
    REPEAT
</code>

This construct also has the advantage that its performance hardly degrades
as the amount of comparisons increase unlike the former method. In the table
below, the same comparisons were performed multiple times to evaluate the
times taken for each. From this it can be seen that INDEX is quicker even if
testing for a single value. (This benchmark was performed on 2.0)

<code>
    Comparisons ³  1    ³  2    ³  3    ³  4    ³  10
    ÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄ
    INDEX       ³  2.03 ³  2.08 ³  2.09 ³  2.11 ³   2.36
    IF n OR n   ³  2.25 ³  3.35 ³  4.45 ³  5.60 ³  12.14
</code>

==== Extracting Parts of Keys ====

When dealing with a two part key (or similar) it is quicker to use the FIELD
function (EG PART1 = FIELD(KEY,"*",1)) than to use the [ ] syntax (EG PART1
= KEY[1,"*"]).

==== Selecting Records From File ====

When selecting records from file for subsequent processing AND THE FIELDS
FORMING THE SELECTION CRITERIA ARE NOT INDEXED it is quicker to extract the
required records by reading in all records and doing the required comparison
in BASIC than by PERFORMing a select. I have seen the latter done at several
sites visited lately and speed improvements of upto 100% have been gained by
adopting the former method (depending on the complexity of he comparison
criteria).


(Volume 1, Issue 10, Pages 8,9)