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Efficient Algorithm for Bit Reversal (from MSB->LSB to LSB->MSB) in C
... Bit Twiddling Hacks page:
Fastest (lookup table):
static const unsigned char BitReverseTable256[] =
{
0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0, 0x10, 0x90, 0x50, 0xD0, 0x30, 0xB0, 0x70, 0xF0,
0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8, 0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF...
Is the “struct hack” technically undefined behavior?
...sed as an array. It's passed to strcpy, in which case it decays to a plain char *, which happens to point to an object which can legally be interpreted as char [100]; inside the allocated object.
– R.. GitHub STOP HELPING ICE
Sep 14 '10 at 23:34
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List columns with indexes in PostgreSQL
...constraint uk_test3ab unique (a, b));
List indexes and columns indexed:
select
t.relname as table_name,
i.relname as index_name,
a.attname as column_name
from
pg_class t,
pg_class i,
pg_index ix,
pg_attribute a
where
t.oid = ix.indrelid
and i.oid = ix.indexreli...
How to keep one variable constant with other one changing with row in excel
...out that you can toggle relative addressing for a formula in the currently selected cells with these keyboard shortcuts:
Windows: f4
Mac: CommandT
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How do I count the number of occurrences of a char in a String?
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Guava equivalent: int count = CharMatcher.is('.').countIn("a.b.c.d"); ...As answered by dogbane in a duplicate question.
– Jonik
Aug 12 '13 at 17:00
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Way to get all alphabetic chars in an array in PHP?
Is there a way to get all alphabetic chars (A-Z) in an array in PHP so I can loop through them and display them?
14 Answers...
Python, remove all non-alphabet chars from string
... MapReduce word count program. Problem is that there are many non-alphabet chars strewn about in the data, I have found this post Stripping everything but alphanumeric chars from a string in Python which shows a nice solution using regex, but I am not sure how to implement it
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Best practices/performance: mixing StringBuilder.append with String.concat
...end(sN).toString();
concat()
String s = s1.concat(s2);
String creates char[] array that can fit both s1 and s2. Copies s1 and s2 contents to this new array. Actually requires less work then + operator.
StringBuilder.append()
Maintains an internal char[] array that grows when needed. No extra ...
Check if a string contains one of 10 characters
I'm using C# and I want to check if a string contains one of ten characters, *, &, # etc etc.
6 Answers
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If strings are immutable in .NET, then why does Substring take O(n) time?
... typically use "substring" to extract a short string -- say, ten or twenty characters -- out of a somewhat longer string -- maybe a couple hundred characters. You have a line of text in a comma-separated file and you want to extract the third field, which is a last name. The line will be maybe a cou...