This issue tracker has been migrated to GitHub, and is currently read-only.
For more information, see the GitHub FAQs in the Python's Developer Guide.

Author trevp
Date 2004-03-26.03:17:02
SpamBayes Score
Marked as misclassified
Sometimes you want to turn a long into a byte-string, 
or vice-versa.  This is useful in cryptographic protocols, 
and probably other network protocols where you need 
to exchange large integers.

In 2.4, you can handle unsigned longs with this:

def stringToLong(s):
    return long(binascii.hexlify(s), 16)

def longToString(n):
    return binascii.unhexlify("%x" % n)

However, these functions are slower than they need to 
be, they're kinda kludgey, and they don't handle 
negative values.

So here's a proposal:

def stringToLong(s):
    return long(s, 256)

def longToString(n):
    return n.tostring()

These functions operate on big-endian, 2's-complement 
byte-strings.  If the value is positive but has its most-
significant-bit set, an extra zero-byte will be 
prepended.  This is the same way OpenSSL and (I think) 
GMP handle signed numbers.

These functions are ~5x faster than the earlier ones, 
they're cleaner, and they work with negative numbers.  

If you only want to deal with unsigned positive numbers, 
you'll have to do some adjustments:

def stringToLong(s):
    return long('\0'+s, 256)

def longToString(n):
    s = n.tostring()
    if s[0] == '\0' and s != '\0':
        s = s[1:]
    return s

That's not ideal, but it seems better than any interface 
change I could think of.

Anyways, the patch adds this to longs.  It should be 
added to ints too, and I guess it needs tests etc..  I 
can help with that, if the basic idea is acceptable.

Date User Action Args
2007-08-23 15:36:54adminlinkissue923643 messages
2007-08-23 15:36:54admincreate