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# -*- coding: utf-8 -*-
#
# Copyright 2011 Sybren A. Stüvel <sybren@stuvel.eu>
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Python compatibility wrappers."""
from __future__ import absolute_import
import sys
from struct import pack
try:
MAX_INT = sys.maxsize
except AttributeError:
MAX_INT = sys.maxint
MAX_INT64 = (1 << 63) - 1
MAX_INT32 = (1 << 31) - 1
MAX_INT16 = (1 << 15) - 1
# Determine the word size of the processor.
if MAX_INT == MAX_INT64:
# 64-bit processor.
MACHINE_WORD_SIZE = 64
elif MAX_INT == MAX_INT32:
# 32-bit processor.
MACHINE_WORD_SIZE = 32
else:
# Else we just assume 64-bit processor keeping up with modern times.
MACHINE_WORD_SIZE = 64
try:
# < Python3
unicode_type = unicode
have_python3 = False
except NameError:
# Python3.
unicode_type = str
have_python3 = True
# Fake byte literals.
if str is unicode_type:
def byte_literal(s):
return s.encode('latin1')
else:
def byte_literal(s):
return s
# ``long`` is no more. Do type detection using this instead.
try:
integer_types = (int, long)
except NameError:
integer_types = (int,)
b = byte_literal
try:
# Python 2.6 or higher.
bytes_type = bytes
except NameError:
# Python 2.5
bytes_type = str
# To avoid calling b() multiple times in tight loops.
ZERO_BYTE = b('\x00')
EMPTY_BYTE = b('')
def is_bytes(obj):
"""
Determines whether the given value is a byte string.
:param obj:
The value to test.
:returns:
``True`` if ``value`` is a byte string; ``False`` otherwise.
"""
return isinstance(obj, bytes_type)
def is_integer(obj):
"""
Determines whether the given value is an integer.
:param obj:
The value to test.
:returns:
``True`` if ``value`` is an integer; ``False`` otherwise.
"""
return isinstance(obj, integer_types)
def byte(num):
"""
Converts a number between 0 and 255 (both inclusive) to a base-256 (byte)
representation.
Use it as a replacement for ``chr`` where you are expecting a byte
because this will work on all current versions of Python::
:param num:
An unsigned integer between 0 and 255 (both inclusive).
:returns:
A single byte.
"""
return pack("B", num)
def get_word_alignment(num, force_arch=64,
_machine_word_size=MACHINE_WORD_SIZE):
"""
Returns alignment details for the given number based on the platform
Python is running on.
:param num:
Unsigned integral number.
:param force_arch:
If you don't want to use 64-bit unsigned chunks, set this to
anything other than 64. 32-bit chunks will be preferred then.
Default 64 will be used when on a 64-bit machine.
:param _machine_word_size:
(Internal) The machine word size used for alignment.
:returns:
4-tuple::
(word_bits, word_bytes,
max_uint, packing_format_type)
"""
max_uint64 = 0xffffffffffffffff
max_uint32 = 0xffffffff
max_uint16 = 0xffff
max_uint8 = 0xff
if force_arch == 64 and _machine_word_size >= 64 and num > max_uint32:
# 64-bit unsigned integer.
return 64, 8, max_uint64, "Q"
elif num > max_uint16:
# 32-bit unsigned integer
return 32, 4, max_uint32, "L"
elif num > max_uint8:
# 16-bit unsigned integer.
return 16, 2, max_uint16, "H"
else:
# 8-bit unsigned integer.
return 8, 1, max_uint8, "B"
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