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Interview Question for Software Engineer at Google:
Jun 25, 2011
You have a 64bit interger counter set to 0. How long it will take to overflow the counter given that you are incrementing it at 4Ghz speed.
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2 of 3 people found this helpful
Jul 2, 2011
If we were to keep it simple and not consider every increment to be a load, increment, store then we basically need 2^64 increments to make the long overflow.
4GHz means 4*(2^30) instructions per second.. which is 2^32
effectively it is (2^64)/(2^32) = 2^32 seconds.. or roughly 136years.
4GHz means 4*(2^30) instructions per second.. which is 2^32
effectively it is (2^64)/(2^32) = 2^32 seconds.. or roughly 136years.
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0 of 1 people found this helpful
Jul 18, 2011
total increments before overflow (tibo) = 2^64
increment speed(is) = 1 second / (4*10^9) increments | 4Ghz = 1x10^9 Hz
total seconds (ts) = 2^64 increments * (1 second /(4*10^9) increments)
ts = 4.611 * 10^9 seconds
total years = ts/(60*60*24*52) = 146.2 years
increment speed(is) = 1 second / (4*10^9) increments | 4Ghz = 1x10^9 Hz
total seconds (ts) = 2^64 increments * (1 second /(4*10^9) increments)
ts = 4.611 * 10^9 seconds
total years = ts/(60*60*24*52) = 146.2 years
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0 of 1 people found this helpful
Jul 18, 2011
total years = ts/(60*60*24*7*52) = 146.2 years
and 4ghz = 4*10^9 Hz
and 4ghz = 4*10^9 Hz
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Jul 22, 2011
Please read the question carefully, it says counter is incrementing at the rate of 4GHz.
i.e, 4GB per second. Not incrementing every second.
So after elapsing first second, counter is at 4GB. After elapsing 2nd second, it is 4 + 4 = 8GB.
64 bit integer is, 2^64 = 2^32 * 2^32. Which is roughly 4GB * 4GB = 16GB.
So per second counter incremented to 4GB, so for 16GB it takes 4 seconds.
i.e, 4GB per second. Not incrementing every second.
So after elapsing first second, counter is at 4GB. After elapsing 2nd second, it is 4 + 4 = 8GB.
64 bit integer is, 2^64 = 2^32 * 2^32. Which is roughly 4GB * 4GB = 16GB.
So per second counter incremented to 4GB, so for 16GB it takes 4 seconds.
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1 of 1 people found this helpful
Sep 17, 2011
Anonymous: 4GB * 4GB != 16 GB. You're ignoring the units!
To be accurate, the answer is 4G * 4G = 16 G^2 = 16 * 2^30 * 2^30.
To be accurate, the answer is 4G * 4G = 16 G^2 = 16 * 2^30 * 2^30.
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