Here is a radically differnt approach to generating primes in pure batch that overperforms everything else I have found . The idea comes from an exercise in Knuth's TAOCP Vol 3 page 617.
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Copy to clipboard1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 | :: prime table using rotating multiples stored in environment
@echo off
setlocal enabledelayedexpansion
mode con cols=90
set @25=-10
set /a num=7,inc1=4,cnt=0,inc2=0,num1=0, maxprime=10000
set lin= 0:
call:line 2 & call:line 3 & call:line 5
:nextnum
if defined @%num% (
for %%i in (!@%num%!) do (
if %%i lss 0 (set /a num1=%num%-%%i,"inc2=-%%i<<1") else (set /a num1=%num%+%%i,"inc2=-(%%i>>1)")
call :aux !num1! !inc2!
)
set @%num%=
) else (
call :line %num%
set /a num1= num * num
if %inc1% equ 4 (set/a "inc2=num<<2") else (set /a "inc2=-(num<<1)")
if !num1! leq %maxprime% set @!num1!=!inc2!
)
set /a num+=inc1, inc1=6-inc1
if %num% lss %maxprime% goto nextnum
echo %lin%
pause & goto:eof
:aux
if %1 leq %maxprime% set @%1=%2 !@%1!
goto:eof
:line formats output in 10 right aligned columns
set num2= %1
set lin=%lin%%num2:~-8%
set /a cnt+=1,res1=(cnt%%10)
if %res1% neq 0 goto:eof
echo %lin%
set cnt1= %cnt%
set lin=%cnt1:~-5%:
goto:eof
|
It's based in keeping a list of multiples of previous found primes around the range we're checking. The numbers not found in the list are primes. For keeping the list I use environment variables of the form @composite=next_increment .It uses a single loop, much faster and degrading slowlier than the nested double loops used in other algorithms. Unforunately a FOR and an auxiliar subroutine are required to overcome the impossiblilty of having repeated keys in environment, as sometimes multiples of different primes clash. Skips multiples of 2 and 3. Outputs primes in lines of 10.
