Lucas-Lehmer Test (Was Classic programming)
Jerome H. Fine
jhfinedp3k at compsys.to
Fri Aug 7 20:37:12 CDT 2015
>>Quite recently, I have a requirement to square very large unsigned
>>integers up to one billion bits [...]
>Are you aware of faster-than-n^2 multiplication algorithms like
Actually, when the algorithm is to square a value, the difficulty
reduces to ONLY
( n^2 + n ) / 2 which is effectively half of the multiply instructions
required when two
different numbers are multiplied. Unfortunately, as you point out, that
until half way to the heat-death of the universe.
IN ADDITION, it is the Lucas-Lehmer primality test:
that I wish to implement (so I can understand the details along with
being able to enjoy the challenge). So the series of one billion bit
multiplications must be repeated (one billion - 2) times.
>Karatsuba, Toom-Cook, or Schönhage-Strassen? If not, you might want to
I have already done that for all three:
Karatsuba algorithm - n1.585
Toom-Cook multiplication - n1.465
One aspect of the Toom-3 algorithm that needs to be solved
is the requirement to divide by 3. There are a number of other
possible Toom-Cook algorithms which divide the initial value
into three or more parts which may also be even faster and might
not require division, but only a shift.
I understand both the Karatsuba and Toom-Cook algorithms
sufficiently to EVENTUALLY implement both at this point.
However, if I use RT-11 under Ersatz-11 as the starting point,
it is highly probable that it will be necessary to use a DLL that
is written in x86 assembler for the actual implementation of
the subroutine to square, subtract two, then take the modulus.
If I can perform each squaring operation in just one second,
it should take only about 5 years to perform the squaring one
One possible improvement might be to activate a second DLL
which executes as a 64-bit program which is called by the
32-bit DLL. Since I expect to have a 64-bit Win7 system
some time this month which I hope to be able to use to run
Ersatz-11 in 32-bit mode, that MIGHT be possible. Can
anyone who reads this comment on IF it is possible to have
an additional thread spawned by a 32-bit DLL running under
64-bit Win7 which will execute as a 64-bit DLL? Since
there is a single 32-bit value which needs to be passed to the
64-bit DLL and a single YES / NO result passed back, that
might be a possible solution which might reduce the execution
time by a factor of four.
Unfortunately, the Schönhage-Strassen algorithm is still beyond
my capability. However, I hope to master it eventually and
implement the code.
>look into them; if you're working with numbers that large, such things
>can make the difference between "practical" and "might finish before
>the heat-death of the universe if we're lucky"...though, admittedly,
>for just simple squaring it's probably not all _that_ bad.
If anyone can comment on my question regarding the
spawning of a 64-bit DLL from a 32-bit DLL running
under a 64-bit Win7, that would be appreciated!!!!!!
Also, a link to information about how to implement the
Schönhage-Strassen algorithm would also be very
More information about the cctalk