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91 lines
3.2 KiB
Python
91 lines
3.2 KiB
Python
#!/usr/bin/env python
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# -*- python -*-
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#BEGIN_LEGAL
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#
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#Copyright (c) 2016 Intel Corporation
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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#
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#END_LEGAL
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import sys
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import os
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import math
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import xedhash
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class linear_func_t(xedhash.hash_fun_interface_t):
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''' This function is used when the keys are sequential '''
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def __init__(self,k,max_key):
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''' @param k: the lowest key in the range
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@param max_key: the highest key in range
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'''
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self.k = k
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self.max_key = max_key - k #used for range validation
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#total number of keys, used for lu table creation
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self.m = self.max_key + 1
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def kind(self):
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return "linear"
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def get_table_size(self):
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return self.m
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def apply(self, x):
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return x - self.k
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def emit_cexpr(self, key_str='key'):
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return "%s - %d" % (key_str,self.k)
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def need_hash_index_validation(self):
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''' the linear function does not need to do hash index validation since
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it does not do hashing'''
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return False
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def add_key_validation(self,strings_dict):
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hidx_str = strings_dict['hidx_str']
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if self.max_key == 0:
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# 2016-07-28 Added an equality test to remove bogus
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# warnings from klocwork (KW) about negative numbers after
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# subtraction on 1-entry hash tables. Many of the linear
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# hashes have one entry and this removes a bunch of
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# completely inappropriate warnings from the frequently
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# stupid klockwork tool.
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return 'if(%s == %d)' % (hidx_str, self.max_key)
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else:
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# 2016-07-28 klockwork complains about unsigned hidx with
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# hidx < 0. I considered adding adding "&& hidx >= 0" to
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# the test to quiet KW warnings. But that extra clause
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# causes the clang compiler to complain that I did
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# something stupid (with -Wall) since that that expression
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# is always true for unsigned numbers. Stupid KW just does
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# not understand unsigned arithmetic. Someone should make
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# KW smarter...
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return 'if(%s <= %d)' % (hidx_str, self.max_key)
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def __str__(self):
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return 'h(x) = linear(x - %d)' % self.k
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def get_linear_hash_function(keylist, tolerable_sparsity=0.2):
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''' returns phash_t object with a linear_funct_t as the hash function'''
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min_key = min(keylist)
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max_key = max(keylist)
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nelem = len(keylist)
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nslots = max_key - min_key + 1
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# if the array is more than 20% empty (or overridden value), bail.
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if nslots > nelem:
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if (nelem * (1.0 + tolerable_sparsity)) < nslots:
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return None
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hash_f = linear_func_t(min_key,max_key)
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return hash_f
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