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It's Official: for LONG1/LONG4, a "byte count" of 0 is taken as a

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shortcut meaning 0L.  This allows LONG1 to encode 0L in two bytes
total.
This commit is contained in:
Tim Peters 2003-01-31 16:43:39 +00:00
parent 757246c189
commit 4b23f2b44b
2 changed files with 25 additions and 9 deletions
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23
Lib/pickle.py
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@ -1291,6 +1291,11 @@ import binascii as _binascii
def encode_long(x):
r"""Encode a long to a two's complement little-endian binary string.
Note that 0L is a special case, returning an empty string, to save a
byte in the LONG1 pickling context.
>>> encode_long(0L)
''
>>> encode_long(255L)
'\xff\x00'
>>> encode_long(32767L)
@ -1307,7 +1312,7 @@ def encode_long(x):
"""
if x == 0:
return '\x00'
return ''
if x > 0:
ashex = hex(x)
assert ashex.startswith("0x")
@ -1316,7 +1321,7 @@ def encode_long(x):
if nibbles & 1:
# need an even # of nibbles for unhexlify
ashex = "0x0" + ashex[2:]
elif ashex[2] >= '8':
elif int(ashex[2], 16) >= 8:
# "looks negative", so need a byte of sign bits
ashex = "0x00" + ashex[2:]
else:
@ -1330,11 +1335,11 @@ def encode_long(x):
if nibbles & 1:
# need an even # of nibbles for unhexlify
nibbles += 1
nbytes = nibbles >> 1
x += 1L << (nbytes * 8)
nbits = nibbles * 4
x += 1L << nbits
assert x > 0
ashex = hex(x)
if x >> (nbytes * 8 - 1) == 0:
if x >> (nbits - 1) == 0:
# "looks positive", so need a byte of sign bits
ashex = "0xff" + x[2:]
@ -1348,6 +1353,9 @@ def encode_long(x):
def decode_long(data):
r"""Decode a long from a two's complement little-endian binary string.
>>> decode_long('')
0L
>>> decode_long("\xff\x00")
255L
>>> decode_long("\xff\x7f")
@ -1362,10 +1370,13 @@ def decode_long(data):
127L
"""
nbytes = len(data)
if nbytes == 0:
return 0L
ashex = _binascii.hexlify(data[::-1])
n = long(ashex, 16)
if data[-1] >= '\x80':
n -= 1L << (len(data) * 8)
n -= 1L << (nbytes * 8)
return n
# Shorthands