On 27 July 2016 at 07:33, Andrew Borodin <boro...@octonica.com> wrote: >>I think we could do carry every 0x7FFFFFF / 10000 accumulation, couldn't we? > > I feel that I have to elaborate a bit. Probably my calculations are wrong. > > Lets assume we already have accumulated INT_MAX of 9999 digits in > previous-place accumulator. That's almost overflow, but that's not > overflow. Carring that accumulator to currents gives us INT_MAX/10000 > carried sum. > So in current-place accumulator we can accumulate: ( INT_MAX - INT_MAX > / 10000 ) / 9999, where 9999 is max value dropped in current-place > accumulator on each addition. > That is INT_MAX * 9999 / 99990000 or simply INT_MAX / 10000. > > If we use unsigned 32-bit integer that is 429496. Which is 43 times > less frequent carring. > > As a bonus, we get rid of 9999 const in the code (: > > Please correct me if I'm wrong. >

This is basically the same problem that has already been solved in mul_var() and other places in numeric.c, so in this case it could be coded using something like accum->maxdig += NBASE - 1; if (accum->maxdig > (INT_MAX - INT_MAX / NBASE) / (NBASE - 1)) Propagate carries... I agree that the new code should avoid explicitly referring to constants like 9999, and I don't think there is any reason for this new code to assume NBASE=10000. Regards, Dean -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers