Set data for each bit in NSData iOS

Question

I created NSData of length 2 bytes (16 bits) and I want to set first 12 bits as binary value of (int)120 and 13th bit as 0 or 1(bit), 14th bit as 0 or 1 (bit) and 15th bit as 0 or 1(bit).

    This is what I want to do:
             0000 0111 1000 --> 12 bits as 120 (int)
             1 <-- 13th bit 
             0 <-- 14th bit
             1 <-- 15th bit
             1 <-- 16th bit

Expected output => 0000 0111 1000 1011 : final binary and convert it to NSData.

How can I do that? Please give me some advice. Thanks all.

Answer 1

This is the exact code you might need:

uint16_t x= 120; //2 byte unsigned int (0000 0000 0111 1000)
//You need 13th bit to be 1
x<<=1; //Shift bits to left .(x= 0000 0000 1111 0000)
x|=1; //OR with 1 (x= 0000 0000 1111 0001)
//14th bit to be 0.
x<<=1; // (x=0000 0001 1110 0010)
//15th bit to be 1
x<<=1; //x= 0000 0011 1100 0100
x|=1;  //x= 0000 0011 1100 0101
//16th bit to be 1
x<<=1; //x= 0000 0111 1000 1010
x|=1;  //x= 0000 0111 1000 1011

//Now convert x into NSData
/** **** Replace this for Big Endian ***************/
NSMutableData *data = [[NSMutableData alloc] init];
int MSB = x/256;
int LSB = x%256;
[data appendBytes:&MSB length:1];
[data appendBytes:&LSB length:1];

/** **** Replace upto here.. :) ***************/
//replace with : 
//NSMutableData *data = [[NSMutableData alloc] initWithBytes:&x length:sizeof(x)];
NSLog(@"%@",[data description]);

Output: <078b> //x= 0000 0111 1000 1011 //for Big Endian : <8b07> x= 1000 1011 0000 0111