pozar@well.UUCP (01/28/87)
Volume 4, Number 4 26 January 1987
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| _ |
| / \ |
| /|oo \ |
| - FidoNews - (_| /_) |
| _`@/_ \ _ |
| International | | \ \\ |
| FidoNet Association | (*) | \ )) |
| Newsletter ______ |__U__| / \// |
| / FIDO \ _//|| _\ / |
| (________) (_/(_|(____/ |
| (jm) |
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Editor in Chief: Thom Henderson
Chief Procrastinator Emeritus: Tom Jennings
FidoNews is the official newsletter of the International FidoNet
Association, and is published weekly by SEAdog Leader, node 1/1.
You are encouraged to submit articles for publication in
FidoNews. Article submission standards are contained in the file
ARTSPEC.DOC, available from node 1/1.
Copyright (C) 1987, by the International FidoNet Association.
All rights reserved. Duplication and/or distribution permitted
for noncommercial purposes only. For use in other circumstances,
please contact IFNA.
Table of Contents
1. ARTICLES
The Logical Technologies VS. Hoard Feil Story
The IBM View of the Universe
Topical TechMail Files
WARNING: System Crashed by User
2. COLUMNS
CRC Calculations
3. NOTICES
The Vote is In!
The Interrupt Stack
Fidonews Page 2 26 Jan 1987
=================================================================
ARTICLES
=================================================================
Brian Walsh, 109/640
Howard Feil
VS
Logical Technologies & Brian Walsh
Recently I finally got the time to catch up on my reading of
Fidonews and while reading Fidonews Volume 3 Number 45 I noticed
an article written by a teenage boy by the name of Howard Feil.
After reading the article I was not the happiest person in the
world.I was also extremely surprised to see it because this child
was logged by my sysop log, AT&T, & My local telephone Company
(C&P telephone) to have been the person who was attempting to
"crash" my Bulletin Board System. My attorney swiftly contacted
his parents regarding the severity of his actions and was offered
a notarized letter stating that his actions against myself & my
company (Logical Technologies) would cease immediately. I
accepted this and dropped all charges and informed AT&T that I
would not prosecute in this matter. After receiving his parents
letter I noticed that I was being Bothered no more and assumed
that the matter was over. I now know I was incorrect. I'm sure
that all of you are wondering what REALLY went on in that
situation that Howard told in Fidonews so I will now tell the
WHOLE Story. Incidentally please keep in mind that I WILL supply
ANYONE who submits a requests with the written evidence proving
that what I am about to write on these electronically generated
pages is the complete truthful story.
On May 19th, 1986 I was Hired to the position of Service
manager to ComputerLand of Howard County in Columbia, MD. While
under there employ in early August I submitted a request to "set-
up" a computer operated Bulletin Board System (BBS) operating
under the fido-net BBS software and to be linked int the Fido-net
electronic mail system in Net 109. My request was approved and I
did so and received the "node number" of 109/640. I then noticed
that the BBS was lacking information that was available for
download and knew that the company would not approve my calling
other BBSs while on company time and my wife wouldn't like my
spending our money to get the information for my employer so I
submitted a request to run a contest in which the first person to
submit 100 different NON-Copyrighted files would receive a Hayes-
Compatible internal Hayes Compatible Modem. That request was also
approved with the Condition that the contest was held with the
knowledge that Brian Walsh was running the contest and that only
He was liable for it. They also stated that I would be able to
purchase the modem at ComputerLand's Cost for the contest. I
accepted those terms and proceeded to "set-up" the contest
information and did supply the information that I was running it
and NOT ComputerLand. At that point the contest started to take
off and I was receiving many good files and Howard Feil (Howard)
was in second place when the problem occurred. First the BBS
Fidonews Page 3 26 Jan 1987
system crashed & I lost everything ( the store would supply the
software to operate the Tape back-up installed in the machine ).
I reconstructed as much as I could and had also kept a written
tally of the contest so I still knew the status of that. I then
found out that the company had entered Chapter 11 and I submitted
my resignation, two weeks notice and a letter stating that I was
removing the BBS from operation when I left because there was no
one working there at that point except for myself. I then placed
a notice on the BBS stating that The system would not be run from
ComputerLand in 2 weeks but from my home and after the move the
contest would continue. All went well with the move and My net
Coordinator, Kurt Reisler, was very understanding and made the
change in the nodelist VERY Quickly. Then I resumed the contest
and it wasn't going very quickly when within one saturday evening
from 11:30pm to 3:00am the next morning I received 47 files from
Howard putting his tally at 107 and placed notice to the public
on the BBS and to him personally. I know now what I did was
premature. While waiting for Howard to log on and see what he had
won I started my own Computer company Logical Technologies. After
He had seen the message and called me by voice and ask if he was
really the winner and I stated to him, "You are the winner and
will be receiving the prize as soon as the files can be verified
to be valid under the rules of the contest." He then said that
that was fine and would be awaiting me to contact him to
"formerly" announce him as the winner. I then check the file and
found them to be in reality approximately 15 different file that
where not Copyrighted, a pirated copy of SideTalk ( a Memory-
resident telecommunications package from Lattice) and a few
trojan programs. The rest were duplicates of the original files
with different file names. I then notified him of this in an
online chat and he replied with, "...well I think you'd BETTER
give my the modem if you want users and a BBS...." I then set his
user level to twit and attempted to continue with the contest but
the interest had died off. I later noticed many users that would
call once and leave a message like "This BBS eats S**T" and so on
and strange enough the user always had a users name of "Howard
Feil." with the rest being some numeric amount. I twitted each
user and after the third user like that I contacted AT&T and C &
P telephone to ask them to put a "Call Log" on my BBS line. they
did and then I noticed that both the users that were using the
name of "Howard Feil."... and the new person attempting to crash
the BBS using the bugs that were in versions prior to 11w (thanks
Tom) were all calling from the same telephone number and that
number was registered to be located in the dwelling where Howard
Feil resided. I then contacted my Attorney and he acted swiftly.
I then was contacted with Howard's parents request to submit a
letter stating that they would guarantee that these actions would
cease. I accepted the offer while thinking of the thing that I
did at his age and knowing the horrors of being "just a kid".
Then All ceased for a bit and then I noticed the article in
fidonews that prompted my present actions including this article.
I am now informing AT&T, C&P telephone and my attorney the I
want this child to "learn a very hard lesson" from his actions.
The charge I am bringing up at present are Slander,Slander with
intent to harm, harassment, & loss of business. AT&T & C&P
Fidonews Page 4 26 Jan 1987
telephone, to the best of my knowledge, are charging him with
Toll Freud and using Federal Communication lines to commit a
crime. Please note that I do not enjoy nor make a habit of doing
this and hope that this article will at least clear my and My
companies name with you the readers of Fidonews. Thanks You.
Sincerely,
Brian Walsh Jr.
President, Logical Technologies
Sysop, Fido 109/640
-----------------------------------------------------------------
Fidonews Page 5 26 Jan 1987
The IBM View of the Universe
In the beginning, there was chaos and the Universe was
without form and void. The Lord looked upon His domain and
decided to declare His presence. "I be" he said, then to correct
his grammar added "am."
If the Lord had decided to work on irregular verb
conjugation first, this wouldn't have happened. God would later
curse the English language for its part, but in that moment IBM
came into being.
The Lord looked out upon the IBM He had created and said
"This is good." That's what He said, but He shook his head,
wondered what the boys at the User Group would say, split the
light from the dark and went to bed. Thus passed the Beginning
and the end of the first day.
On the second day, the Lord summoned IBM unto His presence.
"There is chaos out there, and the Universe is without form and
void. I must correct this and I can use your help. Is there
anything you can do for me?"
"I can take care of form," IBM replied. "Put me in charge of
computers and I will take care of form for you."
The Lord thought that this was good and said "Let there be
computers. Let IBM have my powers of creation that pertain to
computers and form." Thus saying, the Lord went off to His second
day's work while IBM created the 1401.
On the third day, while the Lord was out, IBM decided to
subdivide the assgined task. "Let there be systems that make the
computer work and let them be called Operating Systems. Let
there also be systems that make use of the computer and let them
be called Application Systems." Thus, there came into being both
Operating Systems and Application Systems, but there were no pro-
grammers.
The next morning IBM had to give the Lord a status report.
"What did you do yesterday?" the Lord asked.
"I invented the operating system" IBM replied.
"You did?" the Lord shuddered. "Oh dear."
"Yes I did," IBM confirmed, "but I find I need something you
alone can provide."
"And what is that?"
"I need programmers to use my computers, to operate my
operation system and to apply my applications."
Fidonews Page 6 26 Jan 1987
"That can't be done now," said the Lord. "This is only the
fourth day and there won't be people until the sixth day."
"I need programmers and I need them now. If they can't be
people they can't be people, but we have to work this out today."
"Give me some specifications and I'll see what I can do."
IBM hastily worked up specs for programmers (are specs ever
anything other than hasty) and the Lord reviewed them.
The Lord knew the specs weren't sufficient but followed them
anyway. He also made some programmers that did just what
programmers were supposed to do, just to spite IBM. The
programmers and IBM spent the rest of the day creating the
Assembler and FORTRAN. On the morning of the fifth day, IBM re-
ported to the Lord once again.
"The programmers you created for me have a problem. They
want a programming language that is easy to use and similar to
English. I told them you had cursed English, though I still
don't know why. They wanted me to ask your indulgence on this."
The Lord had cursed English for good reason, but didn't want
to explain this to IBM. He said "let there be COBOL" and that was
that.
On the status report of the next day IBM announced that
computers had gone forth and multiplied. Unfortunately, the
computers still weren't big enough or fast enough to do what the
programmers wanted. The Lord liked the idea of going forth
multiplying, and used the line Himself later on that day. This
sixth day being particularly busy, He declared "Let there be MVS"
and there was MVS.
On the seventh day God had finished creation and computers
had COBOL and MVS. The Lord and IBM took the day off to go
fishing. IBM hung a sign on the door to help programmers in his
absence.
IF AT FIRST YOU DON'T SUCCEED, TRY, TRY AGAIN - AND HAVE THE
FOLLOWING READY BEFORE CALLING IBM.
On the start of the second week the programmers went over
IBM's cathode ray tube directly to God.
"We have a horrible problem," they complained. "Our users
want systems that perform according to their expectations."
"USERS!" the Lord bellowed. "Who said that you should have
users! Users are the difference between good and bad
applications, a function I have reserved unto myself! Who
authorized you to have users?"
"Well, IBM..."
"IBM!! You!! You did this to my programmers! You gave them
Fidonews Page 7 26 Jan 1987
the knowledge of good and evil. For that you shall suffer through
eternity!
"Let there be competition. Let it be called Anacom, and
Burroughs, and CDC."
The Lord went through the alphabet several times. "With all
this competition you shall still suffer the pain of antitrust
legislation all the days of your existence."
This was the start of the second week, and it seems an
appropriate place to conclude our report. In case you missed
something, a summary of key points follows:
1. Users and their needs are and always have been a subject of
dispute. Nobody can learn English because it is cursed by
God. IBM manuals are doubly cursed and therefore twice as hard
to understand. Of the programming languages, only COBOL can
claim divine origin. People are people, but programmers are
something else.
2. Computers may be a gift from heaven, but there's no divine
help in getting them to work. Because of IBM's initial
assignment, there are more forms than anyone knows what to do
with. Finally, chaos was part of the original state of the
Universe and not a product of the data processing industry.
-----------------------------------------------------------------
Fidonews Page 8 26 Jan 1987
Ken McVay, 340/20
Topical EchoMail Files in ASCII Format
Many users have found themselves frustrated when trying to keep
up with the message base in some of the large continental
echomail conferences. With incoming mail increasing that message
base at the rate of perhaps 75-100 messages per day, seven days a
week, it takes real dedication of wade through them!
TECH, one of the popular "continentals," is a case in point. When
I joined the conference, I quickly discovered that no matter how
long the users spent reading the mail, they invariably fell
behind. Quite often, if they missed a span of several days, and
then checked again, they discovered that RENUM had been there
first and clobbered half the mail. Running RENUM on a weekly
basis was a mandatory chore for me, as storage space demanded
that the message base be maintained at under 1MByte.
Another common problem was that TECH contained hundreds of
messages that were of little or no interest to my users. They
were, for instance, concerned with hard drive and DOS-related
issues, and cared little for 80386 vrs. 80286 technical
discussions, or the infamous AMIGA vrs. VAX wars...at first they
tried using the "Inquire" option, but quickly learned that not
only could it not find all the topics they were looking for, but
that it also took a great deal of time searching through the
mail.
When a question related to the DOS PATH command generated dozens
(they are STILL coming it, 6 weeks later!) of replies, I decided
to port them into a text file so users interested in improving
their knowledge of DOS could find all the mail in one place.
Thanks to Rick Duff, the SysOp of the Zanzibar Hotel (Fido
340/11) in Victoria, B.C., who provided me with a delightful
utility (PRINTMSG.COM) for converting FidoMail to ASCII format, I
found it easy to convert the DOS messages, sort them into
chronological order, and group them into a text file. I could
then edit the text file, delete all the SEEN-BY lines, etc. to
reduce storage space, and tuck the resulting files into my DOS
file area, where they could be downloaded or read with the TYPE
command.
To make a long tale less so: There are now several topical text
archives available on my system (some of the un-arc'd ones are
listed below), and more are added as the need arises. The file
names indicate which month's messages are within the file, and
the nature of the topic. Some of these files have grown to over
70K in the course of a month, while others remain quite small. In
particular, both the fixed drive and DOS archives have grown to
the point where they are now mini-encyclopaedias.
My system is a semi-private one, and I have created a "generic"
user to eliminate access delays which often run-up log distance
rates. Those of you who are interested in obtaining these files
Fidonews Page 9 26 Jan 1987
should log on as TECH USER, password TECH. The archives are
stored in file area 16.
3861286 MSG 80386/P-DOS
AUTOCAD MSG CAD/CAM
COMM1186.MSG COMMUNICATIONS
DOS0187 MSG MS-DOS
DPUB0187 MSG DESKTOP PUBLISHING/LASER PRINTERS
FIRM1286 MSG GRAPHICS AND MISC. FIRMWARE
HD1186 MSG FIXED DRIVES
LANTECH MSG LANS
MULT1286 MSG MULTITASKING
PRNT0187 MSG PRINTERS
SEADOG MSG SEADOG
TANDY MSG TANDY 1000PC
V20TECH MSG NEC V-20 CPU
I will be happy to transfer any or all of these files to diskette
for anyone who wants them - the archives presently total 2.25MB,
so you'll need about 7 diskettes to be sure of getting them all.
Please include a decent mailer and return postage - the diskettes
will be returned to you the same day they arrive here.
Ken McVay, 1B Systems Management
1602B Northfield Road, Nanaimo, British Columbia, CANADA V9S 3A7
(VOICE) 604-758-4137 (FIDO) 604-758-4137 (1200 Baud)
-----------------------------------------------------------------
Fidonews Page 10 26 Jan 1987
Sysop, 11/301
WARNING
System Crashed by User
I am the system operator of Fido 11/301. The following sequence
of event occured on January 14, 1987, beginning at 13:30. A Dave
Maxwell logged on, for the first time, according to the log. He
made two attempts to download USER.BBS. The log shows ERROR on
both attempts. He was on for 10 minutes and used the password
ANA. City and State were Asdf Saf. He was on for 10 minutes.
At 13:42 SYSOP successfully logged on. SYSOP is me, of course.
No, I did not do the logging on. Someone had acquired my
password. The user attempted to download *.dog, after changing
the file designation for an area to the fido root directory. He
apparently had a problem and was on for only 5 minutes. Whoever
this was came on again at 13:48, again as SYSOP, and uploaded
ARC.COM to my net mail area. (ARC is an EXE, I think). Anyway,
he then exited to DOS and started to build and ARC file of
somesort in the root directory. I entered the room and saw the
constant disk activity and switched to the bbs partition of
DoubleDos. You can imagine my astonishment to see WatchDog
activated. I then booted the system immediately. The end result
was some problem with cross linked files, possibly caused by the
intruders actions, possibly not. The bottom line is this.
Someone obtained user.bbs. Someone exited to Dos, someone messed
up some files. I have since removed the exit to DOS switch from
runbbs.
Take this as you will. I am making no accusations against
anyone, just repeating what appeared in SYSOP.LOG and what CHKDSK
revealed.
-----------------------------------------------------------------
Fidonews Page 11 26 Jan 1987
=================================================================
COLUMNS
=================================================================
Orv Stoll, 103/531
Sixteen Bit CRC Calculations
Cyclic Redundancy Check or CRC is one of the best error
detection methods available. It is used primarily for serial data
transfers such as disk, tape, and error free serial transfer
protocols. Concentrating on uses found in bulletin boards, CRC's
are used to detect errors in 8 bit data streams such as XMODEM,
KERMIT, and 8 bit data files that are commonly transferred which
could use extra error detection, namely those found in the ARC
program.
There are two common types of CRC calculations used with 8
bit data types. XMODEM and KERMIT use what is called CRC-CCITT
while ARC uses CRC-16. The difference is the polynomial used in
generating the check values. In each of these two methods there
are two different ways that data can be fed through the CRC
generator. The classical method which the CRC instructions and
CRC hardware chips often use is to feed data from each byte least
significant bit first. This is due to the fact that serial data
is sent that way.
The CRC process is defined by polynomial division. The
message is seen as defining a polynomial. As an example consider
a single byte message 01100101, the polynomial this represents is
x^6+x^5+x^2+1. The right most bit is x^0 (or 1) and each bit
left of this is powers 1, 2, and so on. Taking a 128 byte
message such as is found in an XMODEM block, the polynomial it
represents could have powers as high as x^1023. The message
polynomial M(x) is divided by the CRC generating polynomial G(x).
The CRC check sum is the remainder of the division of M(x) * x^16
/ G(x). The G(x) for the CCITT CRC is x^16+x^12+x^5+1 while the
CRC-16 G(x) is x^16+x^15+x^3+1. The idea is that by adding the
remainder to the original message the resultant message when run
through the CRC generator will have a remainder of zero. The
reason for multiplying the message by x^16 is so that the
remainder (which will have an order of x^15 or less) will not
alter the data bits in the message (multiplying M(x) by x^16
simply adds 16 zero bits to the end of the data). Both 16 bit
CRC's have a generating polynomial with x^16 powers in them in
order to yield a 16 bit remainder (CRC check) which can be sent
as exactly two bytes. A G(x) with a power of x^24 would yield 3
bytes and so on. An example using a smaller CRC polynomial and a
short message appears below.
Take a 6 bit message 101101 which would represent the
polynomial x^5 + x^3 + x^2 + 1 and use the generating polynomial
x^4 + x^3 + x. The remainder will be at most a cubic equation
which can be represented by a 4 bit number. The total message
length would be 10 bits. To start the 6 bit message M(x) is
Fidonews Page 12 26 Jan 1987
multiplied by x^4 to allow the remainder to be added to the 6 bit
message without altering its' six bits. The new polynomial to be
divided would be:
x^9 + x^7 + x^6 + x^4 reduced by g(x) * x^5 leaves
-x^8 + x^7 + x^4 reduced by g(x) * -x^4 leaves
2x^7 + x^5 + x^4 reduced by g(x)* 2x^3 leaves
-2x^6 + x^5 - x^4 reduced by g(x)* -2x^2 leaves
3x^5 - x^4 + 2x^3 reduced by g(x)* 3x leaves
-4x^4 + 2x^3 -3x^2 reduced by g(x)* -4 leaves
6x^3 - 3x^2 + 4x.
In columnar form this division looks like:
1 -1 2 -2 3 -4
1 1 0 1 0 | 1 0 1 1 0 1 0 0 0 0
1 1 0 1 0
-1 1 0 0 1
-1 -1 0 -1 0
2 0 1 1 0
2 2 0 2 0
-2 1 -1 0 0
-2 -2 0 -2 0
3 -1 2 0 0
3 3 0 3 0
-4 2 -3 0 0
-4 -4 0 -4 0
6 -3 4 0
If this remainder is added to the original message polynomial
then the remainder should be zero:
1 -1 2 -2 3 -4
1 1 0 1 0| 1 0 1 1 0 1 -6 3 -4 0
1 1 0 1 0
-1 1 0 0 1
-1 -1 0 -1 0
2 0 1 1 -6
2 2 0 2 0
-2 1 -1 -6 3
-2 -2 0 -2 0
3 -1 -4 3 -4
3 3 0 3 0
-4 -4 0 -4 0
-4 -4 0 -4 0
0 0 0 0 0
The new message polynomial is x^9+x^7+x^6+x^4-6x^3+3x^2-4x which
in binary is 101101???0. The problem is how can multiples of a
power that is not zero or one be represented by a single bit,
they can't. For CRC calculations the polynomial division method
is redefined such that negative powers are made positive. Since
remainders in each step will be entirely positive, the remainder
in the next step will only have powers with multipliers 0 or 1.
Fidonews Page 13 26 Jan 1987
The above problem in columnar form now looks like this:
1 1 0 0 1 0
1 1 0 1 0| 1 0 1 1 0 1 0 0 0 0
1 1 0 1 0
1 1 0 0 1
1 1 0 1 0
1 1 0 0 0
1 1 0 1 0
1 0 0
The remainder is simply x^2 which when added will result in the
division:
1 1 0 0 1 0
1 1 0 1 0| 1 0 1 1 0 1 0 1 0 0
1 1 0 1 0
1 1 0 0 1 < note these results
1 1 0 1 0
1 1 0 1 0 <
1 1 0 1 0
0 0 0 0
The result of each subtraction being forced to be positive
results in a bit wise operation that is simply an exclusive or.
In 8088 assembly language the CRC values can be calculated
two ways depending on whether the data is to be taken least or
most significant bit first (for each byte). XMODEM takes the
most significant bit while KERMIT the least. The methods are
both called CRC-CCITT but yield different results and can't be
mixed.
;
; CRC-CCITT accumulator using most significant bit first
; crcval should be set to zero before the first call of this
; routine. AL is sent in having the next character to add
;
crcadd proc near
mov bx,crcval
mov cx,8
crclop: shl al,1
shl bx,1
jnc crcnxt
eor bx,1021h ;or use 8005h for CRC-16
crcnxt: loop crclop
mov crcval,bx
ret
crcadd endp
The above routine could generate CRC-16 values by changing the
eor instruction to:
eor bx,8005h
To generate CRC values with the data shifted in LSBit first the
Fidonews Page 14 26 Jan 1987
body of the routine would look like this:
crcadd proc near
mov bx,crcval
mov cx,8
crclop: shr al,1
shr bx,1
jnc crcnxt
eor 8408h ;for CRC-16 use A001h
crcnxt: loop crclop
mov crcval,bx
ret
When using each of the above routines for generating CRC values,
two bytes of zeros must be fed through crcadd after the message
is sent through but before the crcval is transmitted. On
reception the received CRC bytes should be run through crcadd
after which crcval will be zero if there were no errors. For
example the message "THE" would be run through:
mov crcval,0
mov al,'T'
call send
call crcadd
mov al,'H'
call send
call crcadd
mov al,'E'
call send
call crcadd
mov al,0
call crcadd
mov al,0
call crcadd
mov al,crcval+1 ;send MSB first
call send
mov al,crcval ;then LSB
call send
With a slight change in the CRC accumulator "crcval" will
have a value that includes two zero bytes. This means that they
would not have to be added at the end to finish the CRC
calculation.
crcadd mov cx,8
mov bx,crcval
crclop: shl al,1
jnc nobit
eor bh,80h
nobit: shl bx,1
jnc noeor
eor bx,1021h ;or 8005h for CRC-16
noeor: loop crclop
mov crcval,bx
Fidonews Page 15 26 Jan 1987
ret
When shifting data in LSBit:
crcadd mov cx,8
mov bx,crcval
crclop: shr al,1
jnc nobit
eor bl,1
shr bx,1
jnc noeor
eor bx,8408h ;or a001 for CRC-16
noeor: loop crclop
mov crcval,bx
ret
Although these methods automatically multiply the message by x^16
the loop is slower. The message "THE" using the LSBit routine
above would be sent:
mov al,'T'
call send
call crcadd
mov al,'H'
call send
call crcadd
mov al,'E'
call send
call crcadd
mov al,crcval ;send LSB first
call send
mov al,crcval+1 ;then MSB
call send
The receiver would receive it:
mov crcval,0
call receive
call crcadd
call receive
call crcadd
call receive
call crcadd
call receive
call crcadd
call receive
call crcadd
cmp crcval,0
jnz error
CRC calculations are unusual in that they are more easily
done in assembly than in any high level language (excepting ones
with a CRC function). The process of polynomial division, which
sounds like trouble, turns out to be a snap in assembly, in Basic
though it is trouble. MS Basic won't do "eor"s with anything but
Fidonews Page 16 26 Jan 1987
integer values. They can be in a floating point number but must
be less than 32768. The CRC accumulator uses all bits in an
integer so that the value often gets above 32767 where the EOR
operator will give an overflow error. To get around this the CRC
accumulator needs to be split into two parts. The shift operation
turns into a multiply by 2 operation. Again an overflow will
result if the top bit is remembered and then stripped before the
multiply. If you must code a CRC in Basic be prepared for a very
slow process. The best way is to use the CALL statement and put
the CRC calculator in assembly. It isn't all that hard since the
assembly portion needs no storage for itself. For XMODEM a verbal
procedure would be:
1. Set crcval to zero.
2. For each byte in the block do eight times:
1. Shift the bits of the byte left one position.
2. Shift crcval left one position.
3. If a bit is shifted left of bit 7 in step 2.1 add 1 to
crcval
4. If a bit is shifted left of bit 15 in step 2.2
exclusive or crcval with 0001000000100001 or 1021H
3. If transmitting the block:
1. Repeat 2.1-2.4 with two zero bytes
2. Send block, the upper 8 bits of crcval, then the lower
eight bits of crcval.
4. If receiving the block:
1. crcval should now be zero if there were no errors.
2. The last two bytes of the block should be discarded.
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Fidonews Page 17 26 Jan 1987
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NOTICES
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The Vote is In!
We have not yet received the written report from the CPA, but
we've been told by phone that the results of the bylaws vote are
as follows:
Votes received: 148
Votes in favor: 127
Votes against: 16
Votes disqualified: 5
I am told that the five disqualified votes were disqualified
because the voters were not listed in node list #311, but that
all five were in favor of the proposed bylaws.
In other words, the bylaws were passed by almost eight to one.
We extend our thanks to everyone who took the time out to express
an opinion.
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The Interrupt Stack
17 May 1987
Metro-Fire Fido's Second Birthday BlowOut and Floppy Disk
Throwing Tournament! All Fido Sysops and Families Invited!
Contact Christopher Baker at 135/14 for more information.
24 Aug 1989
Voyager 2 passes Neptune.
If you have something which you would like to see on this
calendar, please send a message to FidoNet node 1/1.
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