хоне ё хӯне خانه یا خونه ؟؟

Hello:)

Farsi like every other language ,has a feature of informal /formal language .

what is the rule of Farsi conversion of "aa" into "u" in these examples ,

naan (bread) >>>noon

xaane (home) >>>xoone

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shaah (king) >>>shah

raah (road) >>>rah

kootaah(short) >>kootah

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what is the phonological even behind this phenomenon?any example in other languages?

Thanks in advance.