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Feature #3429 ยป integer_pow.rb

Eregon (Benoit Daloze), 06/11/2010 10:36 PM

 
power = 7830457
puts power == 105817 * 37 * 2 - 1

def show_last_10_digits(n)
return (puts n) if Float === n and n.infinite? # n == Float::INFINITY or n.infinite? hangs if n is a (big I suppose) Bignum
puts 10.times.map { |i|
n, rest = n.divmod(10)
rest
}.reverse.join # => 8739992577
end

n = 2**power
show_last_10_digits(n)

n = (((2 ** 105817) ** 37) ** 2) / 2
show_last_10_digits(n)

require "prime"
class Integer
def pow(power)
add = 0
until (primes_divisors = Prime.prime_division(power)).size > 1 or prime_division.any? { |prime, pow| pow > 1 }
power += 1
add += 1
end
primes_divisors = primes_divisors.reverse.inject([]) { |pd, (prime, p_pow)| pd + [prime]*p_pow }
n = primes_divisors.inject(self) { |n, prime| n ** prime }
n /= 2**add
n
end
end

n = 2.pow(power)
show_last_10_digits(n)

require "test/unit"
class TestPow < Test::Unit::TestCase
def test_pow
assert_equal 8, 2.pow(3)
assert_equal 16, 2.pow(4)
assert_equal 16, 4.pow(2)
assert_equal 1024**2, 1024.pow(2)
assert_equal 2**1024, 2.pow(1024)
b, p = rand(1000), rand(1000)
p([b,p])
assert_equal b**p, b.pow(p) # sometimes failing, I suppose my Integer#pow is not correct (by example 617**617)
end
end
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