CODEWITHSUNDEEP
c++cbit-manipulation
nevanom
nevanom

Reputation: 380

packing bits into an integer in C++

I want to pack the lowest two bytes of an integer into another in integer, an stuck at this

for ( int i = 0; i < 8 ; i ++){
         if ((bitmask & ( 1 << i)))
             result |= 1 >> i;
     }

Upvotes: 3

Views: 2452

Answers (2)

4rlekin
4rlekin

Reputation: 758

If i understood you correctly sufficient solution should be this:

another_integer = first_integer & 0xFFFF // which is 65536, which is 2^16 so 0000000011111111 binary (for 4 byte integer)

That way you would assign value of two lower bytes of first_integer to the another_integer by using simple AND mask:

0101110011101010
0000000011111111 AND
----------------
0000000011101010

Upvotes: 1

Lundin
Lundin

Reputation: 213306

Endian-independent solution:

x = ((y >> 0) & 0xFF) |
    ((y >> 8) & 0xFF);

Upvotes: 4

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