def pack(fmt, *values):
tfmt, fmt = __get_type(fmt)
if not fmt:
return ()
if tfmt != '.':
raise ValueError('Only variable-length encoding is currently supported')
result = empty_pack
i = 0
for offset, havesize, size, f, val in __pack_iter_fmt(fmt, values):
if f == 'x':
if not havesize:
result += x00
else:
result += x00 * size
# Note: no value, don't increment i
elif f in 'SsUu':
if f == 'S' and '\0' in val:
l = val.find('\0')
else:
l = len(val)
if havesize or f == 's':
if l > size:
l = size
elif (f == 'u' and offset != len(fmt) - 1) or f == 'U':
result += pack_int(l)
if _is_string(val) and f in 'Ss':
result += str(val[:l]).encode()
else:
result += val[:l].encode()
if f == 'S' and not havesize:
result += x00
elif size > l and havesize:
result += x00 * (size - l)
elif f in 't':
# bit type, size is number of bits
if not havesize:
size = 1
if size > 8:
raise ValueError("bit count cannot be greater than 8 for 't' encoding")
mask = (1 << size) - 1
if (mask & val) != val:
raise ValueError("value out of range for 't' encoding")
result += _chr(val)
elif f in 'Bb':
# byte type
if not havesize:
size = 1
for i in range(size):
if f == 'B':
v = val
else:
# Translate to maintain ordering with the sign bit.
v = val + 0x80
if v > 255 or v < 0:
raise ValueError("value out of range for 'B' encoding")
result += _chr(v)
else:
# integral type
result += pack_int(val)
return result
def pack_int(x):
if x < NEG_2BYTE_MIN:
packed = struct.pack('>Q', x & UINT64_MASK)
while packed and packed[0] == xff_entry:
packed = packed[1:]
return _chr(NEG_MULTI_MARKER | getbits(8 - len(packed), 4)) + packed
elif x < NEG_1BYTE_MIN:
x -= NEG_2BYTE_MIN
return _chr(NEG_2BYTE_MARKER | getbits(x, 13, 8), getbits(x, 8))
elif x < 0:
x -= NEG_1BYTE_MIN
return _chr(NEG_1BYTE_MARKER | getbits(x, 6))
elif x <= POS_1BYTE_MAX:
return _chr(POS_1BYTE_MARKER | getbits(x, 6))
elif x <= POS_2BYTE_MAX:
x -= (POS_1BYTE_MAX + 1)
return _chr(POS_2BYTE_MARKER | getbits(x, 13, 8), getbits(x, 8))
elif x == POS_2BYTE_MAX + 1:
# This is a special case where we could store the value with
# just a single byte, but we append a zero byte so that the
# encoding doesn't get shorter for this one value.
return _chr(POS_MULTI_MARKER | 0x1, 0)
else:
packed = struct.pack('>Q', x - (POS_2BYTE_MAX + 1))
while packed and packed[0] == x00_entry:
packed = packed[1:]
return _chr(POS_MULTI_MARKER | getbits(len(packed), 4)) + packed
