Re: [PATCH 2/2] Use fixed-size integers for .idx file I/O

> Simon 'corecode' Schubert <corecode@fs.ei.tum.de> wrote:
> > Morten Welinder wrote:
> > >>-                       return ntohl(*((unsigned int *) ((char *) 
> > >>index + (24 * mi))));
> > >>+                       return ntohl(*((uint32_t *)((char *)index + 
> > >>(24 * mi))));
> > >
> > >Is that pointer gymnastics guaranteed to work?  I.e., how do we know
> > >that we can access an uint32_t (or unsigned) at such an address?
> > 
> > if index is always aligned to a 4-byte boundary, this is safe.  apart from 
> > that, the problem already existed.
> 
> Its always 4-byte aligned here.  The index is mmap()'d as one huge
> chunk so the first byte of the index is page aligned.  The index
> starts out with 256 4-byte words, then is composed of 24 byte units
> (20 byte SHA1, 4 byte offset).  So no worries with the current file
> format, or code.
> 
> Yes, we're taking the leap of faith that any currently-used processor
> will work on 32 bit unsigned integers if they are 4 byte aligned in
> memory.