reorganize dir

Signed-off-by: Mia Steinkirch <mia.steinkirch@gmail.com>

ebook_src/builtin_structures/primes.py

@@ -0,0 +1,47 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+'''
+find prime factors of a number.
+'''
+
+import math
+import random
+
+def find_prime_factors(n):
+    '''
+    >>> find_prime_factors(14)
+    [2, 7]
+    >>> find_prime_factors(19)
+    []
+    '''
+
+    divisors = [d for d in range(2, n//2 + 1) if n % d == 0]
+    primes = [d for d in divisors if is_prime(d)]
+
+    return primes
+
+
+def is_prime(n):
+    for j in range(2, int(math.sqrt(n))):
+        if (n % j) == 0:
+            return False
+    return True
+
+
+''' return a n-bit prime '''
+def generate_prime(number=3):
+    while 1:
+        p = random.randint(pow(2, number-2), pow(2, number-1)-1)
+        p = 2 * p + 1
+        if find_prime_factors(p):
+            return p
+
+
+
+if __name__ == '__main__':
+    import doctest
+    doctest.testmod()
+