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#!/usr/bin/python
# Copyright (C) 2013 Google, Inc.
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Library General Public
# License as published by the Free Software Foundation; either
# version 2 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Library General Public License for more details.
#
# You should have received a copy of the GNU Library General Public License
# along with this library; see the file COPYING.LIB. If not, write to
# the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
# Boston, MA 02110-1301, USA.
# This implementaiton of SuperFastHash is based on the Python implementation
# by Victor Perron at <https://github.com/vperron/python-superfasthash>.
# We've modified Victor's version to output hash values that match WTFString,
# which involves using a specific seed and some different constants.
class uint32_t(long):
def __rshift__(self, other):
return uint32_t(long.__rshift__(self, other) & ((1L << 32) - 1))
def __lshift__(self, other):
return uint32_t(long.__lshift__(self, other) & ((1L << 32) - 1))
def __add__(self, other):
return uint32_t(long.__add__(self, other) & ((1L << 32) - 1))
def __xor__(self, other):
return uint32_t(long.__xor__(self, other) & ((1L << 32) - 1))
def hash(string):
"""
Stream-adapted SuperFastHash algorithm from Paul Hsieh,
http://www.azillionmonkeys.com/qed/hash.html
LGPLv2.1
Python version with no dependencies.
Victor Perron <victor@iso3103.net>
"""
if not string:
return 0
result = uint32_t(0x9E3779B9L)
length = len(string)
remainder = length & 1
length >>= 1
i = 0
while length > 0:
length -= 1
result += ord(string[i])
temp = (ord(string[i + 1]) << 11) ^ result
result = (result << 16) ^ temp
i += 2
result += (result >> 11)
if remainder == 1:
result += ord(string[i])
result ^= (result << 11)
result += (result >> 17)
# Force "avalanching" of final 127 bits
result ^= (result << 3)
result += (result >> 5)
result ^= (result << 2)
result += (result >> 15)
result ^= (result << 10)
# Save 8 bits for StringImpl to use as flags.
result &= 0xffffff
# This avoids ever returning a hash code of 0, since that is used to
# signal "hash not computed yet".
assert result != 0
return result
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