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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 data type to use for hashed password field and what length?
...le numerical value, others have more parameters there (for example to tune CPU usage and RAM usage separately).
The salt. Since the salt must be globally unique, it has to be stored for each account. The salt should be generated randomly on each password change.
The hash proper, i.e. the output of t...
内存优化总结:ptmalloc、tcmalloc和jemalloc - 操作系统(内核) - 清泛网 - ...
...内存到CentralCache里。 解决了ptmalloc2中arena之间不能迁移的问题。
Tcmalloc占用更少的额外空间。例如，分配N个8字节对象可能要使用大约8N * 1.01字节的空间。即，多用百分之一的空间。Ptmalloc2使用最少8字节描述一个chunk。
更快。...
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...
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 ...
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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How much faster is C++ than C#?
...ter will be competing with your code for instruction and data cache in the CPU. We know that cache dominates when it comes to performance and native languages like C++ do not have this type of contention, by definition.
a run-time optimizer's time budget is necessarily much more constrained than th...
Android destroying activities, killing processes
... persistent data, stop animations and other things that may be
consuming CPU, etc. Implementations of this method must be very quick
because the next activity will not be resumed until this method
returns. Followed by either onResume() if the activity returns back to
the front, or onStop() i...
OS detecting makefile
...commended or ideal; they're just what the project to which I was adding OS/CPU auto-detection happened to be using.
ifeq ($(OS),Windows_NT)
CCFLAGS += -D WIN32
ifeq ($(PROCESSOR_ARCHITEW6432),AMD64)
CCFLAGS += -D AMD64
else
ifeq ($(PROCESSOR_ARCHITECTURE),AMD64)
...