The star hash $($Subsets $1,2,3)$It should also check the star magic number $($first byte$)$ of each star, and emit an error if it is incorrect.

HINT:

space$\_$main.c calls the function check$\_$galaxy in space.c when the $-$C option is specified on the

command line.

Add code to check$\_$galaxy in space.c$.$

Call galaxy$\_$hash to calculate hash values.

Think carefully about the functions you can construct to avoid repeated code.

For example, for every byte you read with fgetc you need to call galaxy$\_$hash to calculate a new hash

value, so write a function that does both. Hint: have the function take a pointer to a hash value which it can

update.

Each star ends with a hash $($sometimes referred to as a digest$)$ which calculated from the other values of the star.

This allows us to detect if any bytes of the galaxy have changed, for example by disk or network errors.

The galaxy$\_$hash$()$ function makes one step of computation of the hash of a sequence of bytes:

Given the hash value of the sequence up to this byte, and the value of this byte it calculates the new halue

If we create a galaxy of a single one$-$byte file, like this:

We can then inspect the galaxy, and see its hash is $015.$

Here's the sequence of calls that calculated that value:

void check$\_$galaxy$($char $*$galaxy$\_$pathname$)\{$

$\}$