下面是扩展欧几里得算法的实现。我从Java所采取的代码this answer,推广它,使之与模除2 工作,并把它转换到Python:
def multiplicativeInverse(x, modulus):
if modulus <= 0:
raise ValueError("modulus must be positive")
a = abs(x)
b = modulus
sign = -1 if x < 0 else 1
c1 = 1
d1 = 0
c2 = 0
d2 = 1
# Loop invariants:
# c1 * abs(x) + d1 * modulus = a
# c2 * abs(x) + d2 * modulus = b
while b > 0:
q = a/b
r = a % b
# r = a - qb.
c3 = c1 - q*c2
d3 = d1 - q*d2
# Now c3 * abs(x) + d3 * modulus = r, with 0 <= r < b.
c1 = c2
d1 = d2
c2 = c3
d2 = d3
a = b
b = r
if a != 1:
raise ValueError("gcd of %d and %d is %d, so %d has no "
"multiplicative inverse modulo %d"
% (x, modulus, a, x, modulus))
return c1 * sign;
我给扩展欧几里德算法的实现在回答中到一个单独的问题:http://stackoverflow.com/a/11703184 –
嗯@伍德沃尔看起来内向你的函数我只看到输入参数1。为了计算d,我认为有必要知道变量etf和e,因为问题是(d * e == 1%etf)。 – iuri
d = pow(e,etf-2,etf)仅在etf为素数时才起作用。 – phkahler