Re: [PATCH] document optimizing macro for translating PROT_ to VM_ bits

[Jamie Lokier]

Muli Ben-Yehuda wrote:
> -/* Optimisation macro. */
> +/* Optimisation macro, used to be defined as: */
> +/* ((bit1 == bit2) ? (x & bit1) : (x & bit1) ? bit2 : 0) */ 
> +/* but this version is faster */ 
> +/* "check if bit1 is on in 'x'. If it is, return bit2" */ 
>  #define _calc_vm_trans(x,bit1,bit2) \
>    ((bit1) <= (bit2) ? ((x) & (bit1)) * ((bit2) / (bit1)) \
>     : ((x) & (bit1)) / ((bit1) / (bit2)))

I agree with the intent of that comment, but the code in it is
unnecessarily complex.  See if you like this, and if you do feel free
to submit it as a patch:

/* Optimisation macro.  It is equivalent to:
      (x & bit1) ? bit2 : 0
   but this version is faster.  ("bit1" and "bit2" must be single bits). */

cheers,
-- Jamie
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