Neat idea, but with 2^161 module 2^160 I have a problem. I'll see if I can do something with series.
--Maarten Anton Rolls wrote: > I was helping Oldes with the problem of computing > a long checksum a while back. The code I came up with > is at the bottom. It can give you some ideas maybe. > > Anton. > > >>Hi, >> >>As anybody (efficiently) tackled suntracting two binary! values. I want >>to compute the difference between two 160 bit SHA1 keys, with the >>outcome a new binary. And I also need addition which sould be circular >>in 160bit space. E.g 2^160 + 1 = 1 >> >>Before re-inventing yet another wheel I'd thought I'd ask to see if >>anybody has already written this. >> >>--Maarten > > > ; can use pairs to store integers better and wrap around automatically > ; without math overflow error! :) (Romano's tip) > > sum: 2147483647 > add-val: func [val][ > sum: either error? try [sum + val][ > ; which way did it overflow? (positive/negative) > either positive? sum [ > print "positive" > ; overflowed in positive direction > ; to-integer required because -2147483648 is by default a > decimal > ;print ["(sum + to-integer -2147483648):" (sum + to-integer > -2147483648) > type? (sum + to-integer -2147483648)] > ;print ["(val + to-integer -2147483648):" (val + to-integer > -2147483648) > type? (val + to-integer -2147483648)] > (sum + to-integer -2147483648) + (val + to-integer -2147483648) > ][ > print "negative" > ; overflowed in negative direction > (2147483647 + sum) + (2147483647 + val) + 2 > ] > ][sum + val] ; no error, just add it up > probe type? sum > sum > ] > -- To unsubscribe from this list, just send an email to [EMAIL PROTECTED] with unsubscribe as the subject.
