54 lines
1.5 KiB
Python
54 lines
1.5 KiB
Python
import struct
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# Stolen from PyCypto (Public Domain)
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def b(s):
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return s.encode("latin-1") # utf-8 would cause some side-effects we don't want
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def long_to_bytes(n, blocksize=0):
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"""long_to_bytes(n:long, blocksize:int) : string
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Convert a long integer to a byte string.
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If optional blocksize is given and greater than zero, pad the front of the
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byte string with binary zeros so that the length is a multiple of
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blocksize.
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"""
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# after much testing, this algorithm was deemed to be the fastest
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s = b('')
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pack = struct.pack
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while n > 0:
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s = pack('>I', n & 0xffffffff) + s
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n = n >> 32
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# strip off leading zeros
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for i in range(len(s)):
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if s[i] != b('\000')[0]:
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break
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else:
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# only happens when n == 0
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s = b('\000')
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i = 0
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s = s[i:]
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# add back some pad bytes. this could be done more efficiently w.r.t. the
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# de-padding being done above, but sigh...
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if blocksize > 0 and len(s) % blocksize:
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s = (blocksize - len(s) % blocksize) * b('\000') + s
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return s
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def bytes_to_long(s):
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"""bytes_to_long(string) : long
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Convert a byte string to a long integer.
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This is (essentially) the inverse of long_to_bytes().
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"""
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acc = 0
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unpack = struct.unpack
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length = len(s)
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if length % 4:
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extra = (4 - length % 4)
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s = b('\000') * extra + s
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length = length + extra
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for i in range(0, length, 4):
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acc = (acc << 32) + unpack('>I', s[i:i+4])[0]
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return acc
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