150
The
VIC
20
User
Guide
Keeping time injiffies is useful for timing program speed. This lets you
test the efficiency
of
a program. Consider the following short program:
10
PRINT":.']III!IIKEYBOARD
T£ST!IE!IE":PRINT
20
FOR
1=32
TO
127
30
PRINT
CHR$(I);
40
NEXT
·1
.5~
FOR
J"161
TO
255
60
PRINT
CHR$(J);
70
NEXT
J
S0
PRINT:PRINT:PRINT"!lEilEEND
TEST!lEiIE"
You can compute execution time for this program as follows:
1.
TI (or TIME)
is
assigned
to
a variable at the start
of
the time test.
2.
TI (or
TIME)
is
checked
at
the end
of
the time test. Subtract the first
value
of
TI
from the new
TI
value. This will give you the amount of
jiffy time it
took
to
process the program in question.
The following listing adds these steps:
10
PRINT":')!!!lEKEYBOARD
TEST!IE!IE":PRINT
.
15
A=TI
20
FOR
1=32
TO
127
30
PRINT
CHRS(I)i
40
NE>:T
50
FOR
J=161
TO
255
60
PRINT
CHR$(J);
70
NEXT
80
PRINT:PRINT:PRINT"!IE!lEEND
TEST*!IE"
10e
PRINT:PRINT"TI
=
";TI-A
As
the program continues, TI increments
60
times every second. Line
100
subtracts the first value
of
TI
(A) from TI's latest value.
It
took
41
jiffies
to
display the keyboard characters. Divide jiffy time
(41
jiffies) by
60
(the
number
of
jiffies in a second).
41/60 = 0.6833
Thus, it took 0.6833 seconds to run the program.
RANDOM
NUMBERS
Random
numbers may be used in games you program on your VIC 20;
they have more practical uses in statistics
and
other areas as well. The VIC
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