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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 | b30091890d62 |
children |
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Output Formats</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REL="HOME" TITLE="LW Tool Chain" HREF="index.html"><LINK REL="PREVIOUS" TITLE="Introduction" HREF="c13.html"><LINK REL="NEXT" TITLE="DECB Binaries" HREF="x27.html"></HEAD ><BODY CLASS="CHAPTER" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >LW Tool Chain</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="c13.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="x27.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="CHAPTER" ><H1 ><A NAME="AEN21" ></A >Chapter 2. Output Formats</H1 ><P >The LW tool chain supports multiple output formats. Each format has its advantages and disadvantages. Each format is described below.</P ><DIV CLASS="SECTION" ><H1 CLASS="SECTION" ><A NAME="AEN24" >2.1. Raw Binaries</A ></H1 ><P >A raw binary is simply a string of bytes. There are no headers or other niceties. Both LWLINK and LWASM support generating raw binaries. ORG directives in the source code only serve to set the addresses that will be used for symbols but otherwise have no direct impact on the resulting binary.</P ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="c13.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="x27.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Introduction</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" > </TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >DECB Binaries</TD ></TR ></TABLE ></DIV ></BODY ></HTML >