On Tue, 17 Dec 2019 09:46:52 +1100 Rob Pike <[email protected]> wrote:
> % ivy
> 652342**52342
> 1.85475753442e+304341
>
> )cpu
> 8.291ms
>
> (652342**52342)/34232342
> 9.27378767209e+304340/17116171
>
> )cpu
> 9.217ms
>
> float _
> 5.41814385477e+304333
On plan9/pi4 I get
% ivy
(652342**52342)/34232342
9.27378767209e+304340/17116171
)cpu
181.842ms
Somewhat surprisingly this is better than on linux/pi4:
$ ivy
(652342**52342)/34232342
9.27378767209e+304340/17116171
)cpu
247.783ms
For comparison, gambit-scheme (on linux) takes 126ms.
$ gsi
...
> (time (begin (/ (expt 652342 52342) 34232342) #f))
(time (begin (/ (expt 652342 52342) 34232342) #f))
128 ms real time
126 ms cpu time (116 user, 10 system)
3 collections accounting for 3 ms real time (3 user, 0 system)
545796 bytes allocated
1051 minor faults
1 major fault
#f
But it doesn't have big floats so exact->inexact conversion
returns +inf and takes 15 seconds to do so!
> 50 minutes feels excessive; dc seems to work very hard.
The excessive slow down is dc using nothing fancier than the
grade-school multiplication algorithm that has an O(n^2)
complexity. For large numbers Go's math/big package uses the
Karatsuba algorithm which has is approx. O(n^1.58).
Gambit-Scheme uses the Schönhage–Strassen algorithm for really
large numbers (in addition to Karatsuba where it is better)
but that doesn't matter much for this computation.
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