4ba7209964
git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@137 014f5005-505e-4b48-8d0a-63407b615a7c
43 lines
1.6 KiB
Python
43 lines
1.6 KiB
Python
# -*- coding: utf-8 -*-
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# Relational
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# Copyright (C) 2009 Salvo "LtWorf" Tomaselli
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#
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# Relation is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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#
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# author Salvo "LtWorf" Tomaselli <tiposchi@tiscali.it>
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'''This module contains functions to perform various optimizations on the expression trees.
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The list general_optimizations contains pointers to general functions, so they can be called
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within a cycle.'''
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import optimizer
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def duplicated_select(n):
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'''This function locates and deletes things like
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σ a ( σ a(C)) and the ones like σ a ( σ b(C))'''
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if n.name=='σ' and n.child.name=='σ':
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if n.prop != n.child.prop: #Nested but different, joining them
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n.prop = n.prop + " and " + n.child.prop
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n.child=n.child.child
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duplicated_select(n)
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#recoursive scan
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if n.kind==optimizer.UNARY:
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duplicated_select(n.child)
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elif n.kind==optimizer.BINARY:
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duplicated_select(n.right)
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duplicated_select(n.left)
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return n
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general_optimizations=[duplicated_select] |