What is the trick in pAddress & ~(PAGE_SIZE - 1) to get the page's base address

Posted by Dbger on Stack Overflow See other posts from Stack Overflow or by Dbger
Published on 2010-06-11T15:06:21Z Indexed on 2010/06/11 16:52 UTC
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Following function is used to get the page's base address of an address which is inside this page:

void* GetPageAddress(void* pAddress)
{
    return (void*)((ULONG_PTR)pAddress & ~(PAGE_SIZE - 1));
}

But I couldn't quite get it, what is the trick it plays here?

Conclusion:
Personally, I think Amardeep's explanation plus Alex B's example are best answers. As Alex B's answer has already been voted up, I would like to accept Amardeep's answer as the official one to highlight it! Thanks you all.

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