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Fix possible internal overflow in numeric division.

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div_var_fast() postpones propagating carries in the same way as mul_var(),
so it has the same corner-case overflow risk we fixed in 246693e5ae8a36f0,
namely that the size of the carries has to be accounted for when setting
the threshold for executing a carry propagation step.  We've not devised
a test case illustrating the brokenness, but the required fix seems clear
enough.  Like the previous fix, back-patch to all active branches.

Dean Rasheed
This commit is contained in:
Tom Lane 2015-11-17 15:46:47 -05:00
parent c5ec406412
commit 5f10b7a604
1 changed files with 9 additions and 3 deletions
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12
src/backend/utils/adt/numeric.c
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@ -6266,8 +6266,14 @@ div_var_fast(NumericVar *var1, NumericVar *var2, NumericVar *result,
/*
* maxdiv tracks the maximum possible absolute value of any div[] entry;
* when this threatens to exceed INT_MAX, we take the time to propagate
* carries. To avoid overflow in maxdiv itself, it actually represents
* the max possible abs. value divided by NBASE-1.
* carries. Furthermore, we need to ensure that overflow doesn't occur
* during the carry propagation passes either. The carry values may have
* an absolute value as high as INT_MAX/NBASE + 1, so really we must
* normalize when digits threaten to exceed INT_MAX - INT_MAX/NBASE - 1.
*
* To avoid overflow in maxdiv itself, it represents the max absolute
* value divided by NBASE-1, ie, at the top of the loop it is known that
* no div[] entry has an absolute value exceeding maxdiv * (NBASE-1).
*/
maxdiv = 1;
@ -6293,7 +6299,7 @@ div_var_fast(NumericVar *var1, NumericVar *var2, NumericVar *result,
{
/* Do we need to normalize now? */
maxdiv += Abs(qdigit);
if (maxdiv > INT_MAX / (NBASE - 1))
if (maxdiv > (INT_MAX - INT_MAX / NBASE - 1) / (NBASE - 1))
{
/* Yes, do it */
carry = 0;