About the 'MD5Update()'

[diverger]

Hi, I'm not understand one line in 'MD5Update()' function:

if ((ctx->lo = (saved_lo + size) & 0x1fffffff) < saved_lo)

I compared this line with some others implement, but can't figure out how it works. The 'size' is in bytes right? And the 'saved_lo' is the lower half of the bits counter, right?

Then why here we add a bits counter to a bytes counter?

Thanks