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二维码的生成细节及原理 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...数字分成三组: 012 345 67
2. 把他们转成二进制: 012 转成 0000001100； 345 转成 0101011001； 67 转成 1000011。
3. 把这三个二进制串起来: 0000001100 0101011001 1000011
4. 把数字的个数转成二进制 (version 1-H是10 bits ): 8个数字的二进制是 000000100...
What are the file limits in Git (number and size)?
...s a practical limit, though. I have a repository that's ~8GB with >880,000 files and git gc takes a while. The working tree is rather large so operations that inspect the entire working directory take quite a while. This repo is only used for data storage, though, so it's just a bunch of autom...
What is a rune?
...
With the recent Unicode 6.3, there are over 110,000 symbols defined. This requires at least 21-bit representation of each code point, so a rune is like int32 and has plenty of bits.
– Rick-777
Oct 12 '13 at 12:08
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SQL query to find record with ID not in another table
...
When i have 20 datas, It works, but when i have 20000 datas, it not work, Iam confuse now.
– Frank
Nov 2 '16 at 3:25
1
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Replacing NAs with latest non-NA value
...'a',NA,NA,NA,NA,NA,NA,NA,NA,'b','c','d',NA,NA,NA,NA,NA,'e')
xx = rep(x, 1000000)
system.time({ yzoo = na.locf(xx,na.rm=F)})
## user system elapsed
## 2.754 0.667 3.406
system.time({ yrep = repeat.before(xx)})
## user system elapsed
## 0.597 0.199 0.793
Edit
As this b...
Why is \r a newline for Vim?
...a <Nul> with a search pattern you can just enter CTRL-@ or
"CTRL-V 000". This is probably just what you expect. Internally the
character is replaced with a <NL> in the search pattern. What is unusual is
that typing CTRL-V CTRL-J also inserts a <NL>, thus also searches for ...
Condition within JOIN or WHERE
...ws their SQL benchmarking and they've executed both versions of a sproc 50,000 times at midnight on the dev server and compare the average times.
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What is Double Brace initialization in Java?
...n't take much initialisation time if you do it once. But if you do this 20'000 times throughout your enterprise application... all that heap memory just for a bit of "syntax sugar"?
2. You're potentially creating a memory leak!
If you take the above code and return that map from a method, callers ...
Remap values in pandas column with a dict
...: "G", 8: "H" }
df = pd.DataFrame({ 'col1': np.random.choice( range(1,9), 100000 ) })
and testing with %timeit, it appears that map is approximately 10x faster than replace.
Note that your speedup with map will vary with your data. The largest speedup appears to be with large dictionaries and ...
What makes JNI calls slow?
...st can be linear in the size of the array. I measured JNI copying of a 100,000 array to average about 75 microseconds on my Windows desktop, and 82 microseconds on Mac. Fortunately, direct access may be obtained via GetPrimitiveArrayCritical or NewDirectByteBuffer.
If the method is passed an object,...