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Alignment calculation or something like that

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/** alignment is a power of 2, it is passed in as a hard coded int **/

1. void*p1,**p2

2. int offset = alignment - 1 + sizeof(void*);

3. p2 = (void**)(((size_t)(p1) + offset) & ~(alignment - 1));

4. p2[-1] = p1;


I am trying to understand what/how lines 2 and 3 are doing/calculated.
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Alignment calculation or something like that vijk <vijayx@gmail.com> - 2011-02-01 16:29 -0600
  Re: Alignment calculation or something like that Andreas <a.k.k@nospam.org> - 2011-02-04 12:46 -0600

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