A 32-bit unsigned integer in NSDictionary

I am developing LiveJournal.com client and 开发者_如何学JAVAi have one question. Can u, please, explain what does it mean?

scalar Relevant when security is usemask. A 32-bit unsigned integer representing which of the user's groups of friends are allowed to view this post. Turn bit 0 on to allow any defined friend to read it. Otherwise, turn bit 1-30 on for every friend group that should be allowed to read it. Bit 31 is reserved.

What am i need to add in NSMutableDictionary if i want to see, for example, group with id=6? I don't understand...

The security implementation works by authorizing or no a group of friends to read a journal/text.

This assume there is a maximum of 30 possible groups, as bit-0 is specific, and bit-31 is reserved.

The security is coded on an unsigned int, meaning 32 bits, of which bit0 to bit31 have a special meaning.

• the LSb, bit0, if set to 1 allows any friend the read access.
• if bit0 is 0, it means that the next 30 bits, bit1 to 30, are checked to see if the group i (from bit i) has read access (bit set to 1) or no (bit set to 0).

An unsigned int can be represented as

  bit 31                     bit 0
  v                              v
  bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb

for instance the decimal value of 11 (0...01011, or 8+3) is represented as

  00000000000000000000000000001011

where bit 0, 1 and 3 are set to 1, the others are set to 0.

So, to check if a friend has access to a journal, take the journal access bits, for instance

  11000000000000000000000000001011

you see that the first bit is 1, so all groups (all friends) are authorized.

If the access would be

  11000000000000000000000000001010

the first bit is 0, so you have to check the group number against the access above. Say the group number is 1, you check against the access above

  11000000000000000000000000001010
                                1
                                ^
                        group one

and you see that the group 1 is authorized. If you would have

  11000000000000000000000000001000

the group 1 is not authorized.

For groups 3 and 30, the access is also authorized:

  11000000000000000000000000001000
   *                          *

(The MSb. bit31 is set to 1, but its value is reserved, so you shouldn't bother its value)