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Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_
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Culprit: False Data Dependency (and the compiler isn't even aware of it)
On Sandy/Ivy Bridge and Haswell processors, the instruction:
popcnt src, dest
appears to have a false dependency on the destination register dest. Even though the instruction only...
Pandas timeseries plot setting x-axis major and minor ticks and labels
I want to be able to set the major and minor xticks and their labels for a time series graph plotted from a Pandas time series object.
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Why is pow(a, d, n) so much faster than a**d % n?
I was trying to implement a Miller-Rabin primality test , and was puzzled why it was taking so long (> 20 seconds) for midsize numbers (~7 digits). I eventually found the following line of code to be the source of the problem:
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How do I tar a directory of files and folders without including the directory itself?
...he job in one line. It works well for hidden files as well. "*" doesn't expand hidden files by path name expansion at least in bash. Below is my experiment:
$ mkdir my_directory
$ touch my_directory/file1
$ touch my_directory/file2
$ touch my_directory/.hiddenfile1
$ touch my_directory/.hiddenfile2...
What algorithms compute directions from point A to point B on a map?
...stead of doing Dijkstra's once from source to dest, you start at each end, and expand both sides until they meet in the middle. This eliminates roughly half the work (2*pi*(r/2)^2 vs pi*r^2).
To avoid exploring the back-alleys of every city between your source and destination, you can have several l...
When to use static classes in C# [duplicate]
...ation of helper methods that would otherwise lie around causing redundancy and maintenance hell. They're very easy to use, no instantiation, no disposal, just fire'n'forget. I guess this was my first unwitting attempt at creating a service-oriented architecture - lots of stateless services that just...
Sell me on const correctness
... be changed,
It protects you from making accidental variable assignments, and
The compiler can optimize it. For instance, you are protected from
if( x = y ) // whoops, meant if( x == y )
At the same time, the compiler can generate more efficient code because it knows exactly what the state of...
Querying DynamoDB by date
I'm coming from a relational database background and trying to work with amazon's DynamoDB
7 Answers
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Way to get number of digits in an int?
...thematically, numbers don't have a length, nor do they have digits. Length and digits are both properties of a physical representation of a number in a specific base, i.e. a String.
A logarithm-based solution does (some of) the same things the String-based one does internally, and probably does so ...
Performance difference for control structures 'for' and 'foreach' in C#
...corlib]System.IDisposable::Dispose()
IL_002f: endfinally
} // end handler
IL_0030: ret
} // end of method Test::IterateOverList
The compiler treats arrays differently, converting a foreach loop basically to a for loop, but not List<T>. Here's the equivalent code for an array:
sta...