WOW Walter, it's 4 times faster than the routine I sent! I wonder whether we can use this routine to find the next unknown prime number!
>Hoi peter, Nadya
>
>>
>>create cursor prime ( primenumber i )
>>insert into prime value ( 3 )
>>
>>MaxRange = 100000
>>
>>t = seconds()
>>for i = 5 to MaxRange step 2
>> if IsPrime(i)
>> insert into prime value ( i )
>> endif
>>next
>>? seconds() - t
>>
>>func isprime
>> lpar i
>> local n
>> scan
>> n = prime.primenumber
>> if int( i / n ) = i / n
>> return .f.
>> endif
>> if n^2 > i
>> exit
>> endif
>> endscan
>> return .t.
>>
>
>What about
>
>
>CREATE CURSOR Prime (primenumber i)
>INSERT INTO Prime VALUES (3)
>
>FOR I = 5 TO 100000 STEP 2
> nSQRT = SQRT(i)
> GO TOP
> LOCATE WHILE prime.primenumber =< nSQRT FOR I % prime.primenumber = 0
> IF !FOUND()
> INSERT INTO Prime VALUES ( i )
> ENDIF
>ENDFOR
>
>
>Long live the fast local data engine !! I wonder if VB can do this as fast as VFP.
>So the whole routine Nadya requested can look like the following:
>
>
>SET TALK OFF
>SELECT Numbers
>GO BOTTOM
>MaxRange = Numbers.Num
>
>** Generate Prime numbers
>
>CREATE CURSOR Prime (primenumber i)
>INSERT INTO Prime VALUES (3)
>
>FOR I = 5 TO MaxRange STEP 2
> nSQRT = SQRT(i)
> GO TOP
> LOCATE WHILE prime.primenumber =< nSQRT FOR I % prime.primenumber = 0
> IF !FOUND()
> INSERT INTO Prime VALUES ( i )
> ENDIF
>ENDFOR
>INDEX ON PrimeNumber TAG Prime
>
>** Determine the missing primenumbers in the gaps in the Numtable
>
>CREATE CURSOR Invert (un I)
>SELECT Numbers
>GO TOP
>
>nLow = Num
>SCAN
> FOR nT = nLow+1 TO Num-1
> IF KEYMATCH(nT,1,"Prime")
> INSERT INTO Invert VALUES (nT)
> ENDIF
> ENDFOR
> nLow=Num
>ENDSCAN
>
>
>Walter,
Groet,
Peter de Valença
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