When I was involved in testing the Primary Flight Computers of the Boeing 777 a nice story came to us...
The test pilot, John E. Cashman, before doing any flying with the plane did a very smart thing. He yanked out all the circuit breakers for all the power supplies of the various systems on board. Then powered it all up again. Only about 50% of the systems rebooted properly. Naturally he refused to fly the thing until that was fixed.
I have encountered counter rollovers a few times in the video conferencing systems I've worked on. It's one of those issues where a single glitch is seen only after a system had been running for a few days. It's difficult to debug an issue like that until the bug is correlated with the exact time that a system has been up. Many of the systems I worked on had a default mode where the system would reboot automatically every few days in the middle of the night to work around bugs like that.
I recall a leap year bug that bit all customers who had upgraded to the latest OS on the mini I worked on. On 29th February 1976 the phones began to ring. The mini had no inbuilt clock in those days so the operator had to input the date each morning. You guessed it, the programmer didn't allow for leap years and 1976 was the first leap year this version ran into.
A local patch was soon sorted - an easy thing to do in those days, and the customers were up and running. Such a simple thing that is so easily overlooked!
2000 wasn't an issue for leap years, but while I will not be around, I wonder how many programs will go to 29th February 2100. Remember 2100 is NOT a leap year as its not divisible by 400.
In Oz sometime in the 70's we got BankCard. That was our version of Visa/MasterCard/etc. They were sent by mail to almost everyone who had a bank account, including a lot of children - haha.
Anyway, a friend of mine bought something to try it out. I don't recall the numbers so here is an example.
He had a credit limit of $1000. He spent $100. But he quickly paid it off, and not knowing how much interest might accumulate, he paid back $120 to his card.
Do $1000 less $100 less say $5 interest/charges, plus deposit $120 = $1015 available.
Well there was a bug, and the program realised it was overpaid, but rather than giving him $1015 credit, or even restricting him to $1000, the program deducted the extra $10 from the $1000 leaving him $985.
So now take another example...
$1000 available, you spend $900, charges are $20, you repay $1200.
But $1000-$900-$20=$80, then add $1200=$1280, so the computer takes the overpayment of $280 off your credit limit of $1000, so now you have $720 available.
Now the extreme...
$1000 less $900 spend and less $20 charges =$80. Now you pay $2000.
So the computer calculates $2080 available, less the original $1000 available, and says now have -$1080 available !! So you cannot get your money back because the card is blocked. He tried it and it happened until they fixed the problem
BTW He was a programmer and saw the laugh in it!!!
Yeah Micromite quote 200 million years for their 64 bit millisecond counter to rollover. Gonna sue them if it doesn't...my app needs this to work, darn it!
I have to believe that was tongue in cheek from kwinn...
A bit tongue in cheek perhaps, but count on someone using it to count pico or femto second pulses long enough to overflow even a 64 bit counter when it becomes possible to do so.
I have a great deal of confidence in peoples ingenuity.
Am I the only one who initially thought (based on the thread title) that the 787 was doing "classic" barrel rolls, "counter" to the pilot's control input?
Am I the only one who initially thought (based on the thread title) that the 787 was doing "classic" barrel rolls, "counter" to the pilot's control input?
Nope, not the only one. Some of us see and interpret the world as we'd like it to be. While I occasionally get burned, that may have more or less to do with my pyromanic tendencies...
Am I the only one who initially thought (based on the thread title) that the 787 was doing "classic" barrel rolls, "counter" to the pilot's control input?
Being a computer nerd and as this a computer nerd forum the context implies "counter" as in hardware or software counter and "rollover" as overflowing the number representation in use.
Without that nerdy context "counter rollover" could just be a normal rollover but counter to the normal direction. Which makes no sense at all.
But then what is a "classic" counter rollover or even a "classic" rollover for that matter? And why would it be an issue?
Or did the plane rollover the counter in my local store?
Am I the only one who initially thought (based on the thread title) that the 787 was doing "classic" barrel rolls, "counter" to the pilot's control input?
That blog https://betterembsw.blogspot.co.uk does have some other interesting content. e.g. the latest article explores the statistics of the Tesla statement: "This is the first known fatality in just over 130 million miles where Autopilot was activated. Among all vehicles in the US, there is a fatality every 94 million miles. Worldwide, there is a fatality approximately every 60 million miles." Does that imply that autopilot is safer than human drivers?
Mickster
Posts: 2,611
Comments
What they mean: "You gotta jiggle the handle."
The test pilot, John E. Cashman, before doing any flying with the plane did a very smart thing. He yanked out all the circuit breakers for all the power supplies of the various systems on board. Then powered it all up again. Only about 50% of the systems rebooted properly. Naturally he refused to fly the thing until that was fixed.
A local patch was soon sorted - an easy thing to do in those days, and the customers were up and running. Such a simple thing that is so easily overlooked!
2000 wasn't an issue for leap years, but while I will not be around, I wonder how many programs will go to 29th February 2100. Remember 2100 is NOT a leap year as its not divisible by 400.
In Oz sometime in the 70's we got BankCard. That was our version of Visa/MasterCard/etc. They were sent by mail to almost everyone who had a bank account, including a lot of children - haha.
Anyway, a friend of mine bought something to try it out. I don't recall the numbers so here is an example.
He had a credit limit of $1000. He spent $100. But he quickly paid it off, and not knowing how much interest might accumulate, he paid back $120 to his card.
Do $1000 less $100 less say $5 interest/charges, plus deposit $120 = $1015 available.
Well there was a bug, and the program realised it was overpaid, but rather than giving him $1015 credit, or even restricting him to $1000, the program deducted the extra $10 from the $1000 leaving him $985.
So now take another example...
$1000 available, you spend $900, charges are $20, you repay $1200.
But $1000-$900-$20=$80, then add $1200=$1280, so the computer takes the overpayment of $280 off your credit limit of $1000, so now you have $720 available.
Now the extreme...
$1000 less $900 spend and less $20 charges =$80. Now you pay $2000.
So the computer calculates $2080 available, less the original $1000 available, and says now have -$1080 available !! So you cannot get your money back because the card is blocked. He tried it and it happened until they fixed the problem
BTW He was a programmer and saw the laugh in it!!!
Good idea, I could make use of 64 bit counters, but there would still be overflow problems. Might be less frequent though.
A 64 bit counter will roll over at 18446744073709552000
If we are counting 100ths of seconds I make that about 5.8 billion years.
I guess a Boeing 787 is not going to be powered up that long
A bit tongue in cheek perhaps, but count on someone using it to count pico or femto second pulses long enough to overflow even a 64 bit counter when it becomes possible to do so.
I have a great deal of confidence in peoples ingenuity.
https://en.wikipedia.org/wiki/Boeing_367-80#The_barrel_roll
BTW, that was a 1g roll. Despite any visual disorientation passengers might suffer, no drinks would be spilled!
-Phil
Nope, not the only one. Some of us see and interpret the world as we'd like it to be. While I occasionally get burned, that may have more or less to do with my pyromanic tendencies...
1) Tick = Planck time
2) Epoch = Big Bang
You'll need less than 256 bits for that.
No. I thought the same thing.
Being a computer nerd and as this a computer nerd forum the context implies "counter" as in hardware or software counter and "rollover" as overflowing the number representation in use.
Without that nerdy context "counter rollover" could just be a normal rollover but counter to the normal direction. Which makes no sense at all.
But then what is a "classic" counter rollover or even a "classic" rollover for that matter? And why would it be an issue?
Or did the plane rollover the counter in my local store?
OMG, are we back to the jet on the treadmill question again?
http://www.military.com/video/commercial-aviation/civil-aviation/boeing-707-does-barrel-roll-1955/2935290602001