#!/usr/bin/ruby
#
# The Great Computer Language Shootout
#
http://shootout.alioth.debian.org/#
# Contributed by Glenn Parker, March 2005
def sieve(m)
flags = "\x1" * m
count = 0
pmax = m - 1
2.step(pmax, 1) do |p|
if flags[p] == 1
count += 1
p.step(pmax, p) do |mult|
flags[mult] = 0
end
end
end
count
end
n = (ARGV[0] || 2).to_i
n.step(n - 2, -1) do |exponent|
break if exponent < 0
m = 2 ** exponent * 10_000
count = sieve(m)
printf "Primes up to %8d %8d\n", m, count
end
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