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Added comments to the sort_info_t macros, including the scary pointer

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arithmetic that makes ipos() tick.
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pjcreath
2005-10-17 20:56:51 +00:00
parent 6bcd6c5609
commit ae34187757
1 changed files with 40 additions and 1 deletions
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41
lib/paranoia/isort.h
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@@ -1,5 +1,5 @@
/*
$Id: isort.h,v 1.4 2005/10/15 03:18:42 rocky Exp $
$Id: isort.h,v 1.5 2005/10/17 20:56:51 pjcreath Exp $
Copyright (C) 2004, 2005 Rocky Bernstein <rocky@panix.com>
Copyright (C) 1998 Monty xiphmont@mit.edu
@@ -113,10 +113,49 @@ extern sort_link_t *sort_getmatch(sort_info_t *i, long post, long overlap,
*/
extern sort_link_t *sort_nextmatch(sort_info_t *i, sort_link_t *prev);
/* ===========================================================================
* is()
*
* This macro returns the size of the vector indexed by the given sort_info_t.
*/
#define is(i) (i->size)
/* ===========================================================================
* ib()
*
* This macro returns the absolute position of the first sample in the vector
* indexed by the given sort_info_t.
*/
#define ib(i) (*i->abspos)
/* ===========================================================================
* ie()
*
* This macro returns the absolute position of the sample after the last
* sample in the vector indexed by the given sort_info_t.
*/
#define ie(i) (i->size+*i->abspos)
/* ===========================================================================
* iv()
*
* This macro returns the vector indexed by the given sort_info_t.
*/
#define iv(i) (i->vector)
/* ===========================================================================
* ipos()
*
* This macro returns the relative position (offset) within the indexed vector
* at which the given match was found.
*
* It uses a little-known and frightening aspect of C pointer arithmetic:
* subtracting a pointer is not an arithmetic subtraction, but rather the
* additive inverse. In other words, since
* q = p + n returns a pointer to the nth object in p,
* q - p = p + n - p, and
* q - p = n, not the difference of the two addresses.
*/
#define ipos(i,l) (l-i->revindex)
#endif /* _ISORT_H_ */