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List:       popt-devel
Subject:    Named bit fields ala ancient BSD %b format
From:       Jeff Johnson <n3npq () mac ! com>
Date:       2008-05-01 17:43:17
Message-ID: 09951966-FE5C-4940-A939-A838BEA37758 () mac ! com
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While I'm thinking about popt features, here is another:

The BSD kernel (iirc) devised a means to map bit files to names
using a %b format.

A string was used to map bit# <-> name. E.g. here's an example
from some rpmdb code that I use for output purposes

static const char * dbtFlags =
         "\20\1APPMALLOC\2ISSET\3MALLOC\4PARTIAL\5REALLOC\6USERMEM 
\7DUPOK";

The same technique (of nerdy embedded octal in a string) can be used  
to assign names to bits in a set,
permitting option parsing (using the format string above):

     --option PARTIAL,DUPOK

to save the value 0x48 (i.e. (1 << 3) | (1 << 6)) into the target  
storage.

OTOH, generating the %b format string can be tedious, and perhaps
a more general table like (this from LZMA):

     typedef struct {
         const char *name;
         uint64_t id;
    } name_id_map;

with name = NULL as table end sentinel should be done.

Opinions?

73 De Jeff

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