Adjust bit ranges in specified aobs to set these ranges to unsigned decimal numbers.

adjBits.c

#include <stdio.h>
#include <string.h>
#include <stdint.h>
#include <math.h>

void adjBits(unsigned char* aob, unsigned long long nw,size_t st,size_t ed){
	double st_d=(double)st;
	//double ed_d=(double)ed;
	
	size_t bc=(size_t)( ceil((st_d-1)/8.0));
	unsigned char bbit=0;
	
	for(size_t k=st-1;k<ed;k++)
	{
		bbit=(k)%8;
		if(bbit==0){
			bc+=1;
		}
		char bit= (nw >> (k-st+1)) & 1U;
		aob[bc-1]^=(-bit ^ aob[bc-1]) & ( 1UL <<bbit);
		//printf("%d, %d, %d\n",bc-1,bbit,bit);
	}
	//printf("\n");
}

int main(){
  unsigned char aob[]={0x1D,0x80,0x1E,0x0};
  adjBits(aob, 42,1,14); // change to 42: 1st to 14th
	//printf("\n");
	adjBits(aob, 43,15,32); // change to 43: next 18 bits (32-15+1=18)
	//printf("\n");
  for (size_t i = 0; i < sizeof(aob); ++i){
  		// ith byte is aob[i]
  		printf("%02X ", aob[i]);
	}
   return 0;
}