This is a very basic implementation of a SHA-256 hash according to the FIPS 180-4 standard in C. I did it for educational purposes, the code is not optimized at all, but (almost) corresponds line by line to the standard.
The algorithm to process a small block of data is quite simple and very well described in the standard. I found that correctly implementing the padding is much harder.
It does not have any dependencies (except for the C standard library of course)
and can be compiled with make. When sha256sum is installed, a short test can
be run with make test.
Usage:
./main <input file>