Set data for each bit in NSData iOS - 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

0000011110001011 in bit is 0x07 0x8b in byte.
unsigned char a[2] ;
a[0] = 0x07 ;
a[1] = 0x8b ;
NSData * d = [NSData dataWithBytes:a length:2] ;

Answer 2

Recently i wrote this code for my own project.. Check if this can be helpful to you.
//Create a NSMutableData with particular num of data bytes
NSMutableData *dataBytes= [[NSMutableData alloc] initWithLength:numberOfDataBytes];
//get the byte in which you want to change bit.
char x;
[dataBytes getBytes:&x range:NSMakeRange(bytePos,1)];
//change the bit here by shift operation
x |= 1<< (bitNum%8);
//put byte back in NSMutableData
[dataBytes replaceBytesInRange:NSMakeRange(bytePos,1) withBytes:&x length:1];
Let me know if you need more help ..:)
For changing 13th bit based on string equality
if([myString isEqualTo:#"hello"])
{
char x;
[dataBytes getBytes:&x range:NSMakeRange(0,1)];
//change the bit here by shift operation
x |= 1<< (4%8); // x |=1<<4;
//put byte back in NSMutableData
[dataBytes replaceBytesInRange:NSMakeRange(0,1) withBytes:&x length:1];
}

Answer 3

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