integer.py
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#
# This file is part of pyasn1 software.
#
# Copyright (c) 2005-2019, Ilya Etingof <etingof@gmail.com>
# License: http://snmplabs.com/pyasn1/license.html
#
import sys
try:
import platform
implementation = platform.python_implementation()
except (ImportError, AttributeError):
implementation = 'CPython'
from pyasn1.compat.octets import oct2int, null, ensureString
if sys.version_info[0:2] < (3, 2) or implementation != 'CPython':
from binascii import a2b_hex, b2a_hex
if sys.version_info[0] > 2:
long = int
def from_bytes(octets, signed=False):
if not octets:
return 0
value = long(b2a_hex(ensureString(octets)), 16)
if signed and oct2int(octets[0]) & 0x80:
return value - (1 << len(octets) * 8)
return value
def to_bytes(value, signed=False, length=0):
if value < 0:
if signed:
bits = bitLength(value)
# two's complement form
maxValue = 1 << bits
valueToEncode = (value + maxValue) % maxValue
else:
raise OverflowError('can\'t convert negative int to unsigned')
elif value == 0 and length == 0:
return null
else:
bits = 0
valueToEncode = value
hexValue = hex(valueToEncode)[2:]
if hexValue.endswith('L'):
hexValue = hexValue[:-1]
if len(hexValue) & 1:
hexValue = '0' + hexValue
# padding may be needed for two's complement encoding
if value != valueToEncode or length:
hexLength = len(hexValue) * 4
padLength = max(length, bits)
if padLength > hexLength:
hexValue = '00' * ((padLength - hexLength - 1) // 8 + 1) + hexValue
elif length and hexLength - length > 7:
raise OverflowError('int too big to convert')
firstOctet = int(hexValue[:2], 16)
if signed:
if firstOctet & 0x80:
if value >= 0:
hexValue = '00' + hexValue
elif value < 0:
hexValue = 'ff' + hexValue
octets_value = a2b_hex(hexValue)
return octets_value
def bitLength(number):
# bits in unsigned number
hexValue = hex(abs(number))
bits = len(hexValue) - 2
if hexValue.endswith('L'):
bits -= 1
if bits & 1:
bits += 1
bits *= 4
# TODO: strip lhs zeros
return bits
else:
def from_bytes(octets, signed=False):
return int.from_bytes(bytes(octets), 'big', signed=signed)
def to_bytes(value, signed=False, length=0):
length = max(value.bit_length(), length)
if signed and length % 8 == 0:
length += 1
return value.to_bytes(length // 8 + (length % 8 and 1 or 0), 'big', signed=signed)
def bitLength(number):
return int(number).bit_length()