Raymond Hettinger <[email protected]> added the comment:
def comb64(n, k):
'comb(n, k) in multiplicative group modulo 64-bits'
return (F[n] * Finv[k] * Finv[n-k] & (2**64-1)) << (S[n] - S[k] - S[n - k])
def comb_iterative(n, k):
'Straight multiply and divide when k is small.'
result = 1
for r in range(1, k+1):
result *= n - r + 1
result //= r
return result
def C(n, k):
k = min(k, n - k)
if k == 0: return 1
if k == 1: return n
if k < len(k2n) and n <= k2n[k]: return comb64(n, k) # 64-bit fast case
if k == FixedJ and n <= Jlim: return KnownComb[n] # Precomputed diagonal
if k < 10: return comb_iterative(n, k) # Non-recursive for
small k
j = FixedJ if k > FixedJ and n <= Jlim else k // 2
return C(n, j) * C(n-j, k-j) // C(k, j) # Recursive case
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Python tracker <[email protected]>
<https://bugs.python.org/issue37295>
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