It looks like both the ippsSqrt_32f and ippsSqrt_32f_I return +Inf for a positive denormal number.
See example in https://gist.github.com/yairchu/730ee5fa0368758c7fe8050447c43016 - the output is
This happens with both the latest 2018 Update 3 and in 2017 Update 4.
Looks like a bug unless I'm misunderstanding something.
Thank you for discovering this bug - I've managed to reproduce it.
We'll fix it in the one of the nearest releases, for the current moment I recommend you to use a workaround - ippsSqrt_32f_A24(src, dst, len) function from the ippVM domain (#include ippvm.h).