from hashlib import blake2s
def hash(x): return blake2s(x).digest()[:32]
def values_at_position(n, positions, seed, precompute=False):
values = positions[::]
for round in range(32):
if precompute:
hashvalues = b''.join([
hash(seed + round.to_bytes(1, 'big') + i.to_bytes(4, 'big'))
for i in range((n + 255) // 256)
])
pivot = int.from_bytes(hash(seed + round.to_bytes(1, 'big')), 'big') % n
if precompute:
def permute(pos):
flip = (pivot - pos) % n
maxpos = max(pos, flip)
bit = (hashvalues[maxpos // 8] >> (maxpos % 8)) % 2
return flip if bit else pos
else:
def permute(pos):
flip = (pivot - pos) % n
maxpos = max(pos, flip)
h = hash(seed + round.to_bytes(1, 'big') + (maxpos // 256).to_bytes(4, 'big'))
byte = h[(maxpos % 256) // 8]
bit = (byte >> (maxpos % 8)) % 2
return flip if bit else pos
values = [permute(v) for v in values]
return values
def swap_or_not_shuffle(values, seed):
return [values[i] for i in values_at_position(len(values), list(range(len(values))), seed, True)]
def swap_or_not_shuffle_partial(values, seed, count):
return [values[i] for i in values_at_position(len(values), list(range(count)), seed, False)]
