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Bash tool to get nth line from a file
...huge, you'd better exit after reading the required line. This way you save CPU time See time comparison at the end of the answer.
awk 'NR == num_line {print; exit}' file
If you want to give the line number from a bash variable you can use:
awk 'NR == n' n=$num file
awk -v n=$num 'NR == n' file ...
Explain the use of a bit vector for determining if all characters are unique
...cause operations with bits are very low level and can be executed as-is by CPU. BitVector allows writing a little bit less cryptic code instead plus it can store more flags.
For future reference: bit vector is also known as bitSet or bitArray. Here are some links to this data structure for differen...
What is exactly the base pointer and stack pointer? To what do they point?
...egisters stay where they are, only their value is sent to the RAM from the CPU. In the amd64 mode, this gets a bit more complex, but leave that to another question.
– wigy
Jan 20 '17 at 10:42
...
Building and running app via Gradle and Android Studio is slower than via Eclipse
...ject with gradle files and indexing tasks). Measure build time and process CPU with and without antivirus enabled to see if it is related.
Profiling a build
Gradle has built-in support for profiling projects. Different projects are using a different combination of plugins and custom scripts. Usin...
Why does changing 0.1f to 0 slow down performance by 10x?
... sets FTZ (flush to zero) and DAZ (denormal are zero) in the MXCSR, so the CPU never has to take a slow microcode assist for denormals.
– Peter Cordes
Jan 16 '19 at 10:23
add ...
Evaluating a mathematical expression in a string
...rbitrary commands
eval("9**9**9**9**9**9**9**9", {'__builtins__': None}) # CPU, memory
Note: even if you use set __builtins__ to None it still might be possible to break out using introspection:
eval('(1).__class__.__bases__[0].__subclasses__()', {'__builtins__': None})
Evaluate arithmetic expr...
How to append rows to an R data frame
...t(r)
For 1E5 rows (measurements done on Intel(R) Core(TM) i7-4710HQ CPU @ 2.50GHz):
nr function time
4 data.frame 228.251
3 sqlite 133.716
2 data.table 3.059
1 rbindlist 169.998
0 placebo 0.202
It looks like the SQLite-based sulution, although r...
What is the volatile keyword useful for?
...So if Thread A is creating Singleton instance and just after creation, the CPU corrupts etc, all other threads will not be able to see the value of _instance as not null and they will believe it is still assigned null.
Why does this happen? Because reader threads are not doing any locking and unt...
Lua简明教程 - 脚本技术 - 清泛IT论坛，有思想、有深度
...浮点数会慢（除非大于100,000,000,000,000），或是会有精度问题。你可以以如下的方式表示数字，0x开头的16进制和C是很像的。num = 1024
num = 3.0
num = 3.1416
num = 314.16e-2
num = 0.31416E1
num = 0xff
num = 0x56复制代码
字符串你可以用单引号，也...
How can bcrypt have built-in salts?
...ext.
What is more important : There is no hashing in this process, rather CPU expensive encryption - decryption. thus rainbow tables are less relevant here.
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