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From: Uncle Steve <stevet810@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: Malloc Query
Date: Sat, 21 May 2011 11:13:12 -0400
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On Sat, May 21, 2011 at 02:30:39PM +1200, Ian Collins wrote:
> On 05/20/11 10:34 AM, Uncle Steve wrote:
> 
> A couple of comments on the code:
> 
> <snip>
> 
> >arena_head * arena_creat(size_t s, int n)
> >{
> >    arena_head * h;
> >    int i;
> >
> >    h = malloc(sizeof(arena_head));
> >    if(h == NULL) {
> >       perror("malloc()");
> >       exit(1);
> >    }
> >
> >    h->obj_size = s;
> >    h->arena_size = n;
> >    h->free = n;
> >
> >    h->arena = malloc(s * n);
> >    if(h->arena == NULL) {
> >       perror("malloc()");
> >       exit(1);
> >    }
> >
> >    h->free_list = 0;
> >
> >    for(i = 0; i<  n; i++)
> >       *((int *) arena_obj_addr(h, i)) = i + 1;
> >
> >    *((int *) arena_obj_addr(h, i)) = -1;
> 
> This writes past the end of the allocated block.

Ha, you're right.  The original code this is based on doesn't have
that problem.  The for(;;) comparison should be i < (n - 1).  Since I
wrote it in less than an hour, there ought to be several good bugs in
there.
 
> >    return(h); 
> >}
> >
> >
> >typedef unsigned long long int T64;
> >
> >#define processcputime(p)                                                  
> >\
> 
> Why go the the trouble of declaring this as a messy macro?

I'm not all that interested in nanosecond resolution for timing
things, so I scaled the resolution down to microseconds and turned it
into a 64-bit quantity so arithmetic calculations would be more
convenient.  I suppose it could be a function call, but inline it
probably generates ten or so instructions.  Insulating the actual
system function call also makes porting a little easier.



Regards,

Uncle Steve

-- 
Should a professional politician be charged with molestation if he
kisses babies while attending political rallies?