But here's one random idea: add a successor[] array and an lp_valid[]
array. In the first loop, set lp_valid[offset] = true if it passes the
check_lp() checks, and set successor[A] = B if A redirects to B or has
a CTID link to B, without matching xmin/xmax. Then, in a second loop,
iterate over the successor[] array. If successor[A] = B && lp_valid[A]
&& lp_valid[B], then check whether A.xmax = B.xmin; if so, then
complain if predecessor[B] is already set, else set predecessor[B] =
A. Then, in the third loop, iterate over the predecessor array just as
you're doing now. Then it's clear that we do the lp_valid checks
exactly once for every offset that might need them, and in order. And
it's also clear that the predecessor-based checks can never happen
unless the lp_valid checks passed for both of the offsets involved.
Approach of introducing a successor array is good but I see one overhead with having both successor and predecessor array, that is, we will traverse each offset on page thrice(one more for original loop on offset) and with each offset we have to retrieve
/reach an ItemID(PageGetItemId) and Item(PageGetItem) itself. This is not much overhead as they are all preprocessors but there will be some overhead.
How about having new array(initialised with LP_NOT_CHECKED) of enum LPStatus as below
typedef enum LPStatus
{
LP_NOT_CHECKED,
LP_VALID,
LP_NOT_VALID
}LPStatus;
and validating and setting with proper status at three places
1) while validating Redirect Tuple
2) while validating populating predecessor array and
3) at original place of "sanity check"
something like:
" if (lpStatus[rdoffnum] == LP_NOT_CHECKED)
{
ctx.offnum = rdoffnum;
if (!check_lp(&ctx, ItemIdGetLength(rditem), ItemIdGetOffset(rditem)))
{
lpStatus[rdoffnum] = LP_NOT_VALID;
continue;
}
lpStatus[rdoffnum] = LP_VALID;
}
else if (lpStatus[rdoffnum] == LP_NOT_VALID)
continue;
"
thoughts?
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