Commodore PET - USR

Byte:
3 4
5
6
7
Number Exponent
±MSB
Fraction LSB
1E+38 255
22
118 153
83
1E+10
162
21 2
249
0
1000
138
122 0 0 0
1 129
0
0
00
.01
122
35
215
10
62
1E-4
115
81 183 23 90
lE
62
60
229
8
101
1E-39
0
32 0 0 0
0
0
0
0 0 0
-1
129
128 0 0 0
-1000 138
250 0
0
0
-lE+10
162
149
2
249
0
-1E+38 255
150
118 153
83
The following short program allows you to examine floating point
representations for any numbers.
Line 10 inputs a number that vou enter from
the keyboard. terminating
with a RETURN key. Line 20 points to the beginning of
variables +2 to go pa st the two-byte variable name. Line 30 prints the number
that was input. followed by the five bytes PEEKed from the variable table. The pro-
gram
is continuous; to end. enter a null line (RETURN key only).
10lNPUTA
20 X=PEEK(43)*256+PEEK(42)+2
30 PRINT A;" =" ;PEEK(X) ;PEEK(X+l);PEEK(X+2) ;PEEK(X+3) ;PEEK(X+4)
40 GOTO 10
Integer Variable Format
76
5
4
32
2nd
char
+128
or 128
15t
char
+128
Byte:
r---"T"""':o:--:"-r--"""--
Byte 1 contains the first character of the variable name shifted (+1281.
Byte 2 contains the second character of the variable name shifted (+128), or
if there is no second character, byte 2 contains 128. An integer variable is
denoted by variable names having ASCII values of 176 or higher. The % nota-
tion is dropped from the variable name. Bytes 3 and 4 contain the value of
the integer
in high-byte, low-byte order. (Note that this value is not an address
and does not conform to the reverse standard for
pointers). The value is stored in
twos complement format 50 that the high-order bit (bit 7 of byte 3) represents
the sign. O=positive. and 1=negative.
The remaining three bytes are not used
and are
set to zeros.
The following are sorne examples
of integer representations stored in
the Variable Area. You can use the same
4-line program to look at integer
number representations
after changing A to A% in Iines 10 and 30.
319