ProbablyPrime() is for when the number is too big to test authoritatively. For numbers smaller than that, there are two schools of thought.
The first is to do what you did, doing a primality test for the number at hand. The second is to use a table of results.The table generally needs to be of size N bits, square root (N) bits, or cube root N bits long depending on how much work you are willing to do for each lookup. The Goldilocks size of sqrt is generally best, so for 2^32 that's 2^16 ==> less than 8k bytes. This is small enough that one might have a static table and just use it for 1-2ns prime tests in 0<N<2^32. Or you can build it. My code takes 25538575ns which is ~1/39th of a second. This is easily done in an init() function. The fastest way is determined by the number of different values that you need to test. On Sun, Mar 4, 2018 at 1:40 AM, Jan Mercl <0xj...@gmail.com> wrote: > On Sun, Mar 4, 2018 at 7:27 AM <ralphdoncas...@gmail.com> wrote: > > > It still has room for optimization, but it is much faster than > ProbablyPrime(0) for 32-bit integers. > > http://nerdralph.blogspot.ca/2018/03/fast-small-prime- > checker-in-golang.html > > You may want to give the primality checking functions of > http://github.com/cznic/mathutil a try. > > Running at a Intel® Core™ i5-4670 CPU @ 3.40GHz × 4 machine: > > ~/src/github.com/cznic/mathutil> go test -v -run @ -bench IsPrime |& tee > log > goos: linux > goarch: amd64 > pkg: github.com/cznic/mathutil > BenchmarkIsPrime-4 20000000 70.2 ns/op > BenchmarkIsPrimeUint64-4 500000 2558 ns/op > BenchmarkIsPrimeUint16-4 2000000000 0.28 ns/op > PASS > ok github.com/cznic/mathutil 23.360s > ~/src/github.com/cznic/mathutil> > > -- > > -j > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- Michael T. Jones michael.jo...@gmail.com -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
