CODEWITHSUNDEEP
objective-cbit-manipulation
iamkrillin
iamkrillin

Reputation: 6876

Combine Bit Fields

I'm having a difficult time understanding how to get these bits in the right order

my goal:

given the following inputs

char id = 0x02; //in binary => 0010
char somethingElse = 0xF; //in binary => 1111

how can I obtain the following output

char result = ?; //in binary 0010 1111 (id somethingElse)

Upvotes: 1

Views: 1000

Answers (2)

aLevelOfIndirection
aLevelOfIndirection

Reputation: 3522

I would use a simpler shift operation unless the bits are often modified independently (like bits in the header of some format specification). In this case I would use a combination of a union and bit field. Here is a little program to do this

int main (int argc, const char * argv[])
{
    @autoreleasepool {

        union {
            struct {
                unsigned char id:4;
                unsigned char somethingElse:4;
            } split;
            unsigned char combined;
        } value;

        value.split.id = 0x02;
        value.split.somethingElse = 0xF;

        NSLog(@"%02X", value.combined); // Outputs F2
    }
    return 0;
}

You might want to invert the order of id and somethingElse if this is not the order you want.

Upvotes: 0

Werner Kvalem Vesterås
Werner Kvalem Vesterås

Reputation: 10346

char id = 0x02; //in binary => 0010
char somethingElse = 0xF; //in binary => 1111

char result = (id<<4) | somethingElse;

Upvotes: 2

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