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Improved implementation of some generators thanks to Vincent Demange (http://lita.sciences.univ-metz.fr/~demange/).

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cedricbonhomme 2011-12-30 09:30:15 +01:00
parent 1c568f6095
commit f830226cf8
1 changed files with 16 additions and 18 deletions
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34
stegano/generators.py
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@ -39,19 +39,19 @@ def fermat():
""" """
Generate the n-th Fermat Number. Generate the n-th Fermat Number.
""" """
n = 0 y = 5
while True: while True:
n += 1 yield y
yield pow(2, pow(2, n)) + 1 y = pow(y-1,2)+1
def mersenne(): def mersenne():
""" """
Generate 2^n-1. Generate 2^n-1.
""" """
n = 0 y = 1
while True: while True:
n += 1 yield y
yield pow(2, n) - 1 y = 2*y + 1
def eratosthenes(): def eratosthenes():
""" """
@ -107,20 +107,18 @@ def fibonacci():
yield a yield a
a, b = b, a + b a, b = b, a + b
def syracuse(l=15): def syracuse(l=15):
n = 0 """
Generate the sequence of Syracuse.
"""
y = l
while True: while True:
yield syracuse_gen(n, l) yield y
n += 1 q,r = divmod(y,2)
if r == 0:
def syracuse_gen(n, l=15): y = q
if n == 0: else:
return l y = 3*y + 1
if syracuse_gen(n-1) % 2 == 0:
return syracuse_gen(n-1)/2
elif syracuse_gen(n-1) % 2 == 1:
return 3*syracuse_gen(n-1)+1
if __name__ == "__main__": if __name__ == "__main__":