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http://www.scriptol.org/sieve.php#rebol

Hi, did somebody also notice the speed difference between Vista and 
7 as below?

Benchmark run 27-Aug-2009/16:16:06+2:00. Rebol 2.7.6.3.1
Computer: 100Mega Athlon II X2 250/4G DDR3
OS: Windows Vista 64
Precision: 0.05
Empty block: 104000000.0Hz

Eratosthenes Sieve Prime (size: 8191): 54.0Hz, result: 1899 primes
Four-Banger test (+,-,*,/): 150000.0Hz, result: 10.0

Integral (icount: 10000) of sin(x) 0<=x<=pi/2: 42.7Hz, result: 1.00000000000003

Integral (icount: 10000) of exp(x) 0<=x<=1: 60.2Hz, result: 1.71828182845896
Merge Sort (500 elements): 68.4Hz

Benchmark run 4-Oct-2010/17:00:19+2:00. Rebol 2.7.7.3.1
Computer: 100Mega Athlon II X2 250/4G DDR 3
OS: Windows 7 Professional 64-bit
Precision: 0.05
Empty block: 131000000.0Hz

Eratosthenes Sieve Prime (size: 8191): 69.0Hz, result: 1899 primes
Four-Banger test (+,-,*,/): 188000.0Hz, result: 10.0

Integral (icount: 10000) of sin(x) 0<=x<=pi/2: 49.7Hz, result: 1.00000000000003

Integral (icount: 10000) of exp(x) 0<=x<=1: 74.8Hz, result: 1.71828182845896
Merge Sort (500 elements): 90.4Hz

Benchmark run 4-Oct-2010/17:05:53+2:00. Rebol 2.7.6.3.1
Computer: 100Mega Athlon II 250/4G DDR 3
OS: Windows 7 Professional 64-bit
Precision: 0.05
Empty block: 129000000.0Hz

Eratosthenes Sieve Prime (size: 8191): 71.4Hz, result: 1899 primes
Four-Banger test (+,-,*,/): 188000.0Hz, result: 10.0

Integral (icount: 10000) of sin(x) 0<=x<=pi/2: 51.3Hz, result: 1.00000000000003

Integral (icount: 10000) of exp(x) 0<=x<=1: 75.5Hz, result: 1.71828182845896
Merge Sort (500 elements): 92.5Hz

I'd completely forgotten this group existed :-)

Just as a reminder to anyone else with a sieve-like memory: REBOL.org 
now hosts a mirror of the [web-public] groups in this world too. 
It has (in my opinion) three main improvements over the REBOL.net 
mirror:
1. all posts archived (not just latest 300 per group)

2 (therefore) permanent URLs if you need to point someone to a post
3. áll posts searchable

http://www.rebol.org/cgi-bin/cgiwrap/rebol/aga-groups-index.r?world=r3wp

Using the algorithm: Sieve of Eratosthenes
it's just ligthning fast.
For 50000 max prime, i got those results:

; Eratosthenes 
== 0:00:00.089
; Jerry :-) 
== 0:00:10.099


get-primes: func [n /local primes mul p limit][
	primes: make bitset! n + 1
	p: 2
	limit: square-root n
	for p 2 (to-integer square-root n) 1[
		if p > n [break]
		unless primes/:p [
			mul: p + p
			until [
				primes/:mul: true
				n < mul: mul + p
			]
		]
	]
	primes
]

It returns a bitset. False Bits are prime numbers.

(probably, the real gain comes from using a bitset to store numbers)

box, board, mosaic, matrix, sieve, die, wire, netting, tissue ... 
and the winner is - panel :-)