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Fix bug in like terms collection in expression simplification
Like term collection would lose the actual "variable" part of the term if
the second term collected happened to have no coefficient. This would cause
the expression to take the value of the calculated coefficient which is
obviously wrong.
Thanks to hider <stego@satx.rr.com> for reporting the bug and providing a
proper test case.
Observation: this bug has been present since the first pre-release of
lwtools 3.0 when the algebraic expression system was introduced. Apparently
people tend not to create expressions that trigger the like terms handler.
The specific conditions require the symbol to be undefined and the second
operand to the addition has to have no coefficient so it's likely a fairly
rare scenario. Still, it is somewhat surprising that nobody tripped on it
before now.
author | William Astle <lost@l-w.ca> |
---|---|
date | Mon, 23 Jan 2017 22:58:36 -0700 |
parents | 92cabf300986 |
children |
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#!/bin/sh # # # Copyright 2009 by William Astle <lost@l-w.ca> # #This file is part of LWTOOLS. # #LWTOOLS is free software: you can redistribute it and/or modify it under the #terms of the GNU General Public License as published by the Free Software #Foundation, either version 3 of the License, or (at your option) any later #version. # #This program 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 General Public License for #more details. # #You should have received a copy of the GNU General Public License along with #this program. If not, see <http://www.gnu.org/licenses/>. # this was based somewhat on the "ar" script from gcc6809 # This script is a frontend to the lwar library manager, to make it # look more like GNU ar. Not all ar features are supported here. # It basically translates ar style options into lwar format. # Parse and translate command-line options # ar options cheatsheet: # r: insert (with replace) # c: create archive # u: only replace newer files # v: verbose mode # x: extract files from archive options=$1; shift case $options in rc|cru|-rc|-cru) options="--replace --create" ;; rv) options="--replace" ;; x|-x) options="--extract" ;; -C|--cache) exit 0 ;; *) options="--replace --create $options" if [ "$libname" = "" ]; then libname=$options fi ;; esac if [ "x$options" = "x" ]; then echo "ar (m6809): no options given" exit 1 fi # Run the real lwar with translated options. # --nopaths is given to get the proper standard "ar" behaviour # which doesn't store path names exec lwar --nopaths $options $*