Hi Venkatram,
On Sun, Oct 3, 2010 at 7:28 PM, Venkatram Tummala
<venkatram867@xxxxxxxxx> wrote:
> Hi All,
>
> Can somebody explain the macro pmd_addr_end(addr, end)
>
> #define pmd_addr_end(addr, end) \
> ({ unsigned long __boundary = ((addr) + PMD_SIZE) & PMD_MASK; \
> (__boundary - 1 < (end) - 1)? __boundary: (end); \
> })
>
> I know that this macro rounds the addr value to next higher multiple
> of PMD_SIZE. If this "ceiling" is greater than end, then the value is
> end. What i dont understand is why is "boundary - 1 < end -1" used
> instead of just boundary < end.
When the address happens to fall in the range of the highest PMD
that's addressable, then end wraps to zero (~0 + 1 == 0). end -1 winds
up being ~0. By adding -1 for both boundary and end you don't need to
add special logic to deal with that particular case.
--
Dave Hylands
Shuswap, BC, Canada
http://www.DaveHylands.com/
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