c_cpp/readscorr/bitarray.h

   1 // From http://c-faq.com/misc/bitsets.html
   2 // See also /usr/include/X11/extensions/xtrapbits.h
   3 // Added BITTOGGLE, BITCOPY and BITVALUE without ByteInArray from xtrapbits.h, also change to UPPER case.
   4 // by Hu Xuesong
   5
   6 #ifndef __GA_BITARRAY_H
   7 #define __GA_BITARRAY_H "@(#)bitarray.h 0.1 - 20110428"
   8
   9 #include <limits.h>             /* for CHAR_BIT */
  10
  11 #define BITMASK(b) /* Returns the bit mask of a byte */ \
  12     (1 << ((b) % CHAR_BIT))
  13
  14 #define BITSLOT(b) ((b) / CHAR_BIT) // Just the index of char[]
  15
  16 #define BITSET(a, b) /* Set a specific bit to be True */ \
  17     ((a)[BITSLOT(b)] |= BITMASK(b))
  18
  19 #define BITCLEAR(a, b) /* Set a specific bit to be False */ \
  20     ((a)[BITSLOT(b)] &= ~BITMASK(b))
  21
  22 #define BITTOGGLE(a,b)    /* Toggle a specific bit */ \
  23     ((a)[BITSLOT(b)] ^= BITMASK(b))
  24
  25 #define BITTEST(a, b) /* Test to see if a specific bit is True={1,2,4,8} */ \
  26     ((a)[BITSLOT(b)] & BITMASK(b))
  27
  28 #define BITCOPY(dest,src,bit)   /* Copy a specific bit between TWO bit-arrays*/ \
  29     BITTEST((src),(bit)) ? BITSET((dest),(bit)) : BITCLEAR((dest),(bit))
  30
  31 #define BITVALUE(array,bit)     /* Return True=1 or False=0 depending on bit */ \
  32     (BITSET((array),(bit)) ? 1 : 0)
  33
  34 #define BITNSLOTS(nb) ((nb + CHAR_BIT - 1) / CHAR_BIT) // caltulate the length of char[]
  35
  36 /*
  37 (If you don't have <limits.h>, try using 8 for CHAR_BIT.)
  38
  39 Here are some usage examples. To declare an ``array'' of 47 bits:
  40
  41         char bitarray[BITNSLOTS(47)];
  42
  43 To set the 23rd bit:
  44
  45         BITSET(bitarray, 23);
  46
  47 To test the 35th bit:
  48
  49         if(BITTEST(bitarray, 35)) ...
  50
  51 To compute the union of two bit arrays and place it in a third array
  52 (with all three arrays declared as above):
  53
  54         for(i = 0; i < BITNSLOTS(47); i++)
  55                 array3[i] = array1[i] | array2[i];
  56
  57 To compute the intersection, use & instead of |.
  58
  59 As a more realistic example, here is a quick implementation of the Sieve
  60 of Eratosthenes, for computing prime numbers:
  61
  62 #include <stdio.h>
  63 #include <string.h>
  64
  65 #define MAX 10000
  66
  67 int main()
  68 {
  69         char bitarray[BITNSLOTS(MAX)];
  70         int i, j;
  71
  72         memset(bitarray, 0, BITNSLOTS(MAX));
  73
  74         for(i = 2; i < MAX; i++) {
  75                 if(!BITTEST(bitarray, i)) {
  76                         printf("%d\n", i);
  77                         for(j = i + i; j < MAX; j += i)
  78                                 BITSET(bitarray, j);
  79                 }
  80         }
  81         return 0;
  82 }
  83 */
  84 #endif /* __GA_BITARRAY_H */
  85