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I don't really allow Add/Subtract to overflow.<BR>
In fact I didn't make that change. I removed the overflow in the test case.<BR>
My work is actually finding code that depends on silent overflow.<BR>
<BR>
My usage follows historical usage.<BR>
Even the change I did have, not sure it is still there, returned the correct "false".<BR>
But after possible garbage produced (or the wraparound value))<BR>
<BR>
<BR>
Realize that all my tint/tword code used to use word. There were no checks.<BR>
<BR>
<BR>
Ok, some overflow I'm allowing is like here, so I must have kept a change in ToInt:<BR>
<BR>
IF (NOT TInt.ToInt(imm, ins.imm)) AND (NOT TWord.LE(imm, Target.Word32.max)) THEN<BR> t.Err("immOp1: unable to convert immediate to INTEGER:" & Target.TargetIntToDiagnosticText(imm));<BR> END;<BR><BR>
IF (NOT TInt.ToInt(imm, ins.imm)) AND (NOT TWord.LE(imm, Target.Word32.max)) THEN<BR> t.Err("movImmT: unable to convert immediate to INTEGER:" & Target.TargetIntToDiagnosticText(imm));<BR> END;<BR><BR>
IF (NOT TInt.ToInt(src.imm, ins.imm)) AND (NOT TWord.LE(src.imm, Target.Word32.max)) THEN<BR> t.Err("pushOp: unable to convert immediate to INTEGER:" & Target.TargetIntToDiagnosticText(src.imm));<BR> END;<BR><BR>
It really is around some type ambiguity.<BR>
Is the value signed or unsigned?<BR>
Maybe we need TWord.ToWord(Word.T)?<BR>
I think that is the simple answer really. Overflow checking good, no need to proceed with an answer, as long as we have a variant for conversion to 0..2^n. For now TInt.ToInt is what I use, a bit off.<BR>
<BR>
- Jay<BR><BR> <BR>
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From: hosking@cs.purdue.edu<BR>Date: Wed, 10 Feb 2010 10:18:24 -0500<BR>To: jkrell@elego.de<BR>CC: m3commit@elegosoft.com<BR>Subject: Re: [M3commit] CVS Update: cm3<BR><BR>Jay, I think your usage of TInt and TWord is strongly at odds with its intended use. Certainly, allowing TInt.Add/Subtract to overflow will break large swaths of the front-end. There is a deep contract there that requires that TInt arithmetic not provide bogus results.
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<DIV>On 10 Feb 2010, at 12:58, Jay Krell wrote:</DIV><BR class=ecxApple-interchange-newline>
<BLOCKQUOTE>
<DIV>CVSROOT:<SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span> </SPAN>/usr/cvs<BR>Changes by:<SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span> </SPAN>jkrell@birch.<SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span> </SPAN>10/02/10 12:58:11<BR><BR>Modified files:<BR><SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span></SPAN>cm3/m3-sys/m3back/src/: Stackx86.m3 <BR><BR>Log message:<BR><SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span></SPAN>allow negating FIRST(INTEGER) even though it overflows<BR><SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span></SPAN>allows this test case to compile:<BR><SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span></SPAN>C:\dev2\cm3.2\m3-sys\m3tests\src\p1\p137>cm3<BR><SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span></SPAN>--- building in NT386 ---<BR><SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span></SPAN><BR><SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span></SPAN>new source -> compiling Main.m3<BR><SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span></SPAN>"..\Main.m3", line 35: doneg: Negate overflowed<BR><SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span></SPAN>1 error encountered<BR><SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span></SPAN>compilation failed => not building program "pgm.exe"<BR><SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span></SPAN>Fatal Error: package build failed<BR><SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span></SPAN><BR><SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span></SPAN>tempting to make TInt.Add/Subtract return the value<BR><SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span></SPAN>even if overflow, but for now, no.<BR><SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span></SPAN>This fix assumes two's complement, that is,<BR><SPAN style="WHITE-SPACE: pre" class=ecxApple-tab-span></SPAN>it assumes FIRST(INTEGER) = -FIRST(INTEGER)<BR></DIV></BLOCKQUOTE></DIV><BR></DIV> </body>
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