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Annotation of coherent/a/usr/man/ALL/bitfields, revision 1.1

1.1     ! root        1: 
        !             2: 
        !             3: bit-fields                  Definition                 bit-fields
        !             4: 
        !             5: 
        !             6: 
        !             7: 
        !             8: A bit-field is  a member of a structure or  union that is defined
        !             9: to be  a cluster of  bits.  It provides  a way to  represent data
        !            10: compactly.  For example, in the following structure
        !            11: 
        !            12: 
        !            13:         struct example {
        !            14:                 int member1;
        !            15:                 long member2;
        !            16:                 unsigned int member3 :5;
        !            17:         }
        !            18: 
        !            19: 
        !            20: member3 is declared to be a bit-field that consists of five bits.
        !            21: A  colon `:'  precedes the integral  constant that  indicates the
        !            22: _w_i_d_t_h, or  the number of  bits in the bit-field.   Also, the bit-
        !            23: field declarator  must include a type, which must  be one of int,
        !            24: signed int, or unsigned int.
        !            25: 
        !            26: A bit-field that  is not given a name may  not be accessed.  Such
        !            27: an object  is useful as  ``padding'' within an object  so that it
        !            28: conforms to a template designed elsewhere.
        !            29: 
        !            30: A bit-field that is unnamed and  has a length of zero can be used
        !            31: to force adjacent bit-fields into separate objects.  For example,
        !            32: in the following structure
        !            33: 
        !            34: 
        !            35:         struct example {
        !            36:                 int member1;
        !            37:                 int member2 :5;
        !            38:                 int :0;
        !            39:                 int member3 :5;
        !            40:         };
        !            41: 
        !            42: 
        !            43: the zero-length bit-field  forces member2 and member3 to be writ-
        !            44: ten into separate objects.
        !            45: 
        !            46: Finally, it is illegal to take the address of a bit-field.
        !            47: 
        !            48: ***** See Also *****
        !            49: 
        !            50: bit, bit map, byte, definitions
        !            51: 
        !            52: ***** Notes *****
        !            53: 
        !            54: Because bit-fields  have many implementation-specific properties,
        !            55: they are  not considered to  be highly portable.   Bit-fields use
        !            56: minimal amounts of  storage, but the amount of computation needed
        !            57: to  manipulate and  access them  may  negate this  benefit.  Bit-
        !            58: fields  must  be  kept  in  integral-sized objects  because  many
        !            59: machines  cannot directly  access a  quantity of  storage smaller
        !            60: than a ``word'' (a word is generally used to store an int).
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        !            62: 
        !            63: 
        !            64: COHERENT Lexicon                                           Page 1
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