Documentation

i2osp converts a positive integer into a byte string

first byte is MSB (most significant byte), last byte is the LSB (least significant byte)

os2ip converts a byte string into a positive integer

just like i2osp, but take an extra parameter for size. if the number is too big to fit in len bytes, nothing is returned otherwise the number is padded with 0 to fit the len required.

just like i2ospOf except that it doesn't expect a failure: i.e. an integer larger than the number of output bytes requested

for example if you just took a modulo of the number that represent the size (example the RSA modulo n).