@related: [[C]] [[byte]] [[java]] [[algo]] [[bit.fr]] [[bit.en]] [[limit]]

  * http://www-graphics.stanford.edu/~seander/bithacks.html
  * http://publications.gbdirect.co.uk/c_book/chapter6/bitfields.html


==== ENDIANS ====

  #define IS_BIG_ENDIAN (*(uint16_t *)"\0\xff" < 0x100)

  * http://msdn.microsoft.com/en-us/library/ms819743.aspx
  * http://stackoverflow.com/questions/2100331/c-macro-definition-to-determine-big-endian-or-little-endian-machine


==== bit shifting ====

<code>
/// emulate's java's unsigned shift : '>>>'
#define MACRO_BITSHIFT_TYPE(type, value, offset)                             \
  (((offset) > 0) ?                                                     \
  ((((value) >> 1)                                                   \
    & (~(((type)1) << ((sizeof(value) << 3) - 1)))) >> ((offset) - 1)) \
   : ((offset) == 0 ) ? (value) :  ((value)<<(offset))            \
   )

#define BITSHIFT(value, offset)                      \
 MACRO_BITSHIFT_TYPE(typeof(value), value, offset)
</code>


==== power of 2 ====

  * http://www.catch22.net/tuts/c-c-tricks

  #define ISPOW2(x)  (x && !(x & (x-1)))


  /// O(1)
  #define ISPOW2(x) (((-x)&(x))==(x))

  template <typename T> inline bool ISPOW2(const T &a)  { return (a) > 0 && ((a) & ((a)-1)) == 0;  }


  /// O(32)
  #include <stdio.h>
  int isPower2(unsigned int n) {
    if ( ! n ) return n; /* n=0 in register */
    for(;;(n>>=1)) { if ( n & 0x1 ) { return ( !  (n>>=1) ); } }
  }
  int main (int argc, char** argv) {
   int r;
   unsigned int i=0;
   if ( argc >1 )  i = atoi(argv[1]);
   r = isPower2( i );
   printf("# %d is %sa power of 2\n", i , ( r ) ? "" : "not " );
   return r;
  }

Endian: 4 char to uint32 : 

<code>
  u32<<=8;
  u32|=( buff[i+3] &0xFF);
  u32<<=8;
  u32|=( buff[i+2] &0xFF);
  u32<<=8;
  u32|=( buff[i+1] &0xFF);
  u32<<=8;
  u32|=( buff[i+0] &0xFF);
</code>


==== MorE ====

{{http://i.huffpost.com/gadgets/slideshows/246711/slide_246711_1426175_free.jpg}}