🚀 go-pugleaf

In article <4je1p1$g1s@solutions.solon.com>
schwarz@mips.complang.tuwien.ac.at (Konrad Schwarz) writes:

|> I posted the following suggestion for a ``packed array'' of bits yesterday:

|> |> If you are interested in space, one suggestion is
|> |> 
|> |>   # include   <limits.h>
|> |>   
|> |>   # define    UNSIGNED_BIT    (CHAR_BIT * sizeof (unsigned))
|> |> 
|> |>   struct {
|> |>       unsigned the_bits [UNSIGNED_BIT]: 1;
|> |>   } the_array [800][(800 + UNSIGNED_BIT - 1) / UNSIGNED_BIT];
|> |> 
|> |>   # define    BIT(X, Y)\
|> |>       the_array [Y][(X) / UNSIGNED_BIT].the_bits [(X) % UNSIGNED_BIT]

|> Upon further reflection, I now am more inclined toward the following:

|>  struct {
|>      unsigned b [800][800]:1;
|>  } the_array;

So what does your compiler have to say about it?  According to all of
the documation I've read (including ISO 9899), bit fields must have
integral types.  And an array is not an integral type.

I've generally used the following macros (BM: Bit Map):

    #define BM_SIZE( n )        ((n) / CHAR_BITS + ((n) % CHAR_BITS != 0))
    #define BM_ISSET( b , n )   \
        (((b)[ (n) / CHAR_BITS ] & (1 << ((n) % CHAR_BITS))) != 0)
    #define BM_SET( b , n )     \
        ((b)[ (n) / CHAR_BITS ] |= (1 << ((n) % CHAR_BITS)))
    #define BM_RESET( b , n )   \
        ((b)[ (n) / CHAR_BITS ] &= ~(1 << ((n) % CHAR_BITS)))


    /*  For a bitmap of `unsigned char'                     */
    char                bm[ BM_SIZE( UCHAR_MAX + 1 ) ] ;
    memset( bm , 0 , sizeof( bm ) ) ;
    BM_SET( bm , (unsigned char)( 'a' ) ) ;
    if ( BM_ISSET( bm , (unsigned char)( 'b' ) )
        ...

Care is needed in their use, since they evaluate there arguments several
times, but I've found them quite useful in the past.
-- 
James Kanze           (+33) 88 14 49 00          email: kanze@gabi-soft.fr
GABI Software, Sarl., 8 rue des Francs Bourgeois, 67000 Strasbourg, France
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