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lexical #3/19, attach and instantly remove a NULL wl_word here 

this modification is faithful iff cw != NULL  and  cw->wl_next == NULL
  cw != NULL because we have just survived an update of cw->wl_word
  cw->wl_next == NULL is witnessed by:
    1) cw either NULL or pointing to a wl_cons(,NULL)
    2) cw not being modified, and no wl_next being modified
    3) check of all function invocations with wlist/cw argument
         not to modify any wl_next slot
which are:
  1) cp_ccom(wlist, ...)
  2) wl_free() always followed by goto nloop, which does a cw = wl_cons(,NULL)

and cp_ccom() doesn't modify any wl_next slot

the first part of the patch is intentionally similar to newword
`i' and `buf' can be modified here, because we will inevitably `goto done'
attach and instantly remove a NULL wl_word here
This commit is contained in:
rlar 2012-07-31 20:39:03 +02:00
parent ddebb63425
commit 80191f3d44
1 changed files with 12 additions and 0 deletions
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12
src/frontend/parser/lexical.c
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@ -185,6 +185,18 @@ gotchar:
if (i) {
buf[i] = '\0';
cw->wl_word = copy(buf);
// assumption: cw != NULL and cw->wl_next == NULL
cw->wl_next = wl_cons(NULL, NULL);
cw->wl_next->wl_prev = cw;
cw = cw->wl_next;
// note: we can overwrite buf and i here
// they won't be accessed any more (see `goto done')
bzero(buf, NEW_BSIZE_SP);
i = 0;
// cw->wl_prev is the recent cw
// thus this wl_next has been NULL per assumtion vrom above
cw->wl_prev->wl_next = NULL;
tfree(cw);
} else {
if (cw->wl_prev) {
cw->wl_prev->wl_next = NULL;