Is const-correctness paranoia good?

Yes, definitely. Lets see this simple example:

$ cat test.cpp
int test(int x) {
 if (x = 1)
  return 42;
 else
  return 0;
}
$ g++ -c test.cpp
$ g++ -c -Wall test.cpp
int test(int x) {
 if (x = 1)
  return 42;
 else
  return 0;
}

Only when we turn on warnings, compiler tell us about a possible error. Making the parameter const shows us error:

$ cat test2.cpp
int test(int x) {
 if (x = 1)
  return 42;
 else
  return 0;
}
$ g++ -c test.cpp
test2.cpp: In function ‘int test(int)’:
test2.cpp:2:8: error: assignment of read-only parameter ‘x’
  if (x = 1)
        ^

All input parameters should be const, all write-once variables serving as a parameters for some computations should be also const.

Quick and dirty ad-hoc git hosting

Recently I needed to synchronize my local repository with a remote machine, just for full backup. It's really simple if you have standard Linux tools (Cygwin works too, of course).

1. in a working directory run:

$ pwd
/home/foo/project
$ git update-server-info

2. in a parent directory start HTTP server:

$ cd ..
$ pwd
/home/foo
$ python -m SimpleHTTPServer
Serving HTTP on 0.0.0.0 port 8000 ...

3. on a remote machine clone/pull/whatever:

$ git clone http://your_ip:8000/project/.git

Step 1 have to be executed manually when local repository has changed.

Scalar version of SSE move mask instruction

SSE instruction PMOVMSKB gathers all most significant bits from bytes and stores them as a single 16-bit value; similar action is performed by MOVMSKPD and MOVMSKPS.

Such operation could be easily done using scalar multiplication. Read more ...

Asymmetric numeral systems

Very interesting idea: Asymmetric numeral systems: entropy coding combining speed of Huffman coding with compression rate of arithmetic coding.

C++ standard inaccuracy

First we read:

21.4.1 basic_string general requirements [string.require]
[...]
3 No erase() or pop_back() member function shall throw any exceptions.

... few pages later:

21.4.6.5 basic_string::erase [string::erase]
basic_string<charT,traits,

Allocator>& erase(size_type pos = 0, size_type n = npos);
[...]
2 Throws: out_of_range if pos > size().

SIMD-friendly Rabin-Karp modification

Rabin-Karp algorithm uses a weak hash function to locate possible substring positions. This modification uses merely equality of first and last char of searched substring, however equality of chars can be done very fast in parallel, even without SIMD instruction. Read more ...

GCC - asm goto

Starting from GCC 4.5 the asm statement has new form: asm goto. Programmer can use any labels from C/C++ program, however output from this block is not allowed.

Using asm block in old form required more instructions and additional storage:

 uint32_t bit_set;
 asm (
  "bt %2, %%eax  \n"
  "setc %%al  \n"
  "movzx %%al, %%eax \n"
  : "=a" (bit_set)
  : "a" (number), "r" (bit)
  : "cc"
 );

 if (bit_set)
  goto has_bit;

Above code is compiled to:

 80483f6:       0f a3 d8                bt     %ebx,%eax
 80483f9:       0f 92 c0                setb   %al
 80483fc:       0f b6 c0                movzbl %al,%eax
 80483ff:       85 c0                   test   %eax,%eax
 8048401:       74 16                   je     8048419 

With asm goto the same task could be writting shorter and easier:

 asm goto (
  "bt %1, %0 \n"
  "jc %l[has_bit] \n"

  : /* no output */
  : "r" (number), "r" (bit)
  : "cc"
  : has_bit // name of label
 );

Complete demo is available. See also GCC documentation about Extended Asm.