Need metaprogrammed magic to determine the matte length of bit fields without errors

Question

The goal is to control which types of users can perform which operations at the user interface level. This code has been in place for a while; I just want to improve it a bit. The file I'm trying to improve should probably be automatically generated, but it will be too large to modify, so I'm looking for a simpler solution.

The file we will call PermissionBits.hhas the following sequence:

// Here names are mangled; for example XYZ_OP_A is:
// permission to operation A in category/context XYZ
// SCU64 = static const unsigned __int64
// Some namespaces utilize all 64 bits
// The actual values (as long as they are proper bit fields) 
// do not matter - they are always used by name
namespace XYZPermissionBits
{
    SCU64 XYZ_OP_A = 1UI64 <<  0; //    1 = 0x0000000000000001
    SCU64 XYZ_OP_B = 1UI64 <<  1; //    2 = 0x0000000000000002
    SCU64 XYZ_OP_C = 1UI64 <<  2; //    4 = 0x0000000000000004
    SCU64 XYZ_OP_C = 1UI64 <<  3; //    8 = 0x0000000000000008
    SCU64 XYZ_OP_D = 1UI64 <<  4; //   16 = 0x0000000000000010
    SCU64 XYZ_OP_E = 1UI64 <<  5; //   32 = 0x0000000000000020
    SCU64 XYZ_OP_F = 1UI64 <<  6; //   64 = 0x0000000000000040
    SCU64 XYZ_OP_G = 1UI64 <<  7; //  128 = 0x0000000000000080
    SCU64 XYZ_OP_H = 1UI64 <<  8; //  256 = 0x0000000000000100
    SCU64 XYZ_OP_I = 1UI64 <<  9; //  512 = 0x0000000000000200
    SCU64 XYZ_OP_J = 1UI64 << 10; // 1024 = 0x0000000000000400
    SCU64 XYZ_OP_K = 1UI64 << 11; // 2048 = 0x0000000000000800
    SCU64 XYZ_OP_L = 1UI64 << 12; // 4096 = 0x0000000000001000 
}

Even with the 1UI64 << <numBits>;shortcut, there are still problems, because encoders create flags with duplicate values, make typos, etc.

Ideally, I need a macro that can be nicely formatted and looks like this:

BITFIELDS_FOR_NAMESPACE(
    //*************** <<== I want to make the namespace name more vivid
    XYZPermissionBits,
    //*************** <<== somehow if that is possible. It is not a must-have.
    XYZ_OP_A, // Being able to add a comment here would be nice, but not critical
    XYZ_OP_B,
    XYZ_OP_C,
    XYZ_OP_D,
    XYZ_OP_E,
    XYZ_OP_F,
    XYZ_OP_G,
    XYZ_OP_H,
    XYZ_OP_I,
    XYZ_OP_J,
    XYZ_OP_K,
    XYZ_OP_L
)

, 2 65 - namespace name + 64 flags. , , ? ?

Answer 1

Boost.PreProcessor:

#include <boost/preprocessor/seq/for_each_i.hpp>
#include <boost/preprocessor/comparison/greater.hpp>
#include <boost/preprocessor/comparison/less.hpp>
#include <boost/preprocessor/debug/assert.hpp>
#include <boost/preprocessor/seq/size.hpp>

#define CHECK_SIZE(size) \
  BOOST_PP_ASSERT_MSG(BOOST_PP_GREATER(size, 1), "<  2 :(") \
  BOOST_PP_ASSERT_MSG(BOOST_PP_LESS(size, 65),   "> 64 :(") \

#define DO_MAKE_BITFIELDS(a, b, i, elem) \
  SCU64 elem = 1UI64 << i;

#define BITFIELDS_FOR_NAMESPACE(name, seq) \
  CHECK_SIZE(BOOST_PP_SEQ_SIZE(seq)) \
  namespace name { \
    BOOST_PP_SEQ_FOR_EACH_I(DO_MAKE_BITFIELDS, _, seq) \
  }

:

BITFIELDS_FOR_NAMESPACE(
    XYZPermissionBits,
    (XYZ_OP_A)
    (XYZ_OP_B)
    // ...
);

Answer 2

IFAIK, http://www.boost.org/doc/libs/1_43_0/libs/preprocessor/doc/index.html .

Answer 3

, Cog.

Cog python ++ ( ), Cog python , . . python .

cog, :

namespace XYZPermissionBits
{
    /* [[[cog
    import cog
    operations = ["A", "B", "C", "D", 
                  "E", "F", "G", "H",
                  "I", "J", "K", "L"]

    assert 2 <= len(operations) <= 64

    for idx,op in enumerate(operations):
        cog.outl("SCU64 XYZ_OP_%s = 1UI64 << %s;" % (op, idx))

    ]]] */
    SCU64 XYZ_OP_A = 1UI64 << 0;
    SCU64 XYZ_OP_B = 1UI64 << 1;
    SCU64 XYZ_OP_C = 1UI64 << 2;
    SCU64 XYZ_OP_D = 1UI64 << 3;
    SCU64 XYZ_OP_E = 1UI64 << 4;
    SCU64 XYZ_OP_F = 1UI64 << 5;
    SCU64 XYZ_OP_G = 1UI64 << 6;
    SCU64 XYZ_OP_H = 1UI64 << 7;
    SCU64 XYZ_OP_I = 1UI64 << 8;
    SCU64 XYZ_OP_J = 1UI64 << 9;
    SCU64 XYZ_OP_K = 1UI64 << 10;
    SCU64 XYZ_OP_L = 1UI64 << 11;
// [[[end]]]
}

Answer 4

//etc , . . , . , , , "op" A, B, C ( ), D...

Answer 5

- . MAKE_THINGS, :

#define MAKE_THINGS \
  MAKE_THING(NAME1) \
  MAKE_THING(NAME2) \
  MAKE_THING(NAME3) \
  /* Include semantically-blank line after list */

MAKE_THING, , MAKE_THINGS, undefine MAKE_THING. :

:

#define MAKE_THINGS \
  MAKE_THING(HAPPY,"Happy") \
  MAKE_THING(SAD_AND_BLUE,"Sad and blue") \
  MAKE_THING(SLEEPY,"Sleepy") \
  /* Include semantically-blank line after list */

#define MAKE_THING(x,y) NUMBER_##x,
typedef enum {MAKE_THINGS LAST_THING} THING_NUMBER;
#undef MAKE_THING

#define MAKE_THING(x,y) FLAG_##x = (1L << NUMBER##x),
typedef enum {MAKE_THINGS ALL_FLAGS = (1 << LAST_THING)-1} THING_FLAGS;
#undef MAKE_THING

#define MAKE_THING(x,y) const char *MSG_##x = y;
MAKE_THINGS
#undef MAKE_THING

#define MAKE_THING(x,y) MSG_##x,
const char *thing_names[] = {MAKE_THINGS 0};
#undef MAKE_THING

Please note that all ads are automatically saved in parallel. Each thing receives a number (0..N-1), a flag (a bit corresponding to its number), a message line and a place in the array of message lines.