1. Prime Numbers
Do you happen to need to know all the prime numbers between, say,
8,123,456,789,000,000 and 8,123,456,790,000,000?
Or maybe you'd just like to say for sure if 6,000,000,016,333,021 is a prime
Can you figure this out with dBASE or FoxPro?
The answer is yes, no problemo.
Okay, here's the story: I was cleaning house the other day and I ran across a
bench marking program I wrote back in my QA engineer days at Borland (I updated
it slightly a couple of years ago when I got my CD writer). I never published
this program and it is certainly obsolete but I thought someone might find it
interesting. It's tricky. I store all the primes within a range of 30 numbers
in a single byte. So, the primes within a range of 1 million numbers gets
stored in a table of only 34 k.
This code runs without modification under dBASE IV 2.0, dBASE 5, or FoxPro v
2.5 (it probably runs under other DOS versions but these are the ones I tested
with). It writes a log file with elapsed times for each range of 1 million.
So, I found it useful for speed benchmarking--comparing xBase versiions and
also comparing hardware setups.
The program uses a table of primes (all primes under 100 million) to facilitate
finding larger primes. If the program doesn't find this table then it
generates it. This will take a long time (perhaps overnight or even days on
slow systems). If you want to skip this step, you could dowload this starter
set of primes. The file is called
http://www.go2zero.com/1st100ml.dbf (it's about 3.3 megabytes)
Once you have the first 100 million table, it takes only about 10 seconds on a
fast system to find all the primes in a range of one million (for smallish
primes, say under 100 billion). The quadrillions take longer of course.
Here's the code:
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