Shamira Changeset - c6815615a077

Changeset - c6815615a077

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Laman - 4 years ago 2020-12-18 12:07:10

gfmul caching

1 file changed with 2 insertions and 1 deletions:

src/shamira/gf256.py

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src/shamira/gf256.py

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 # GNU GPLv3, see LICENSE
 """Arithmetic operations on Galois Field 2**8. See https://en.wikipedia.org/wiki/Finite_field_arithmetic"""
 from functools import reduce
+from functools import reduce, cache
 import operator
 def _gfmul(a, b):
 	"""Basic multiplication. Russian peasant algorithm."""
 	res = 0
@@ @@ -26,12 +26,13 @@ for i in range(256): @@
 	L[acc] = i
 	acc = _gfmul(acc, g)
 L[1] = 0
 INV = [E[255-L[i]] if i!=0 else None for i in range(256)]  # multiplicative inverse
 @cache
 def gfmul(a, b):
 	"""Fast multiplication. Basic multiplication is expensive. a*b==g**(log(a)+log(b))"""
 	assert 0<=a<=255, 0<=b<=255
 	if a==0 or b==0: return 0
 	t = L[a]+L[b]
 	if t>255: t -= 255

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