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<p><font size="2" face="sans-serif">In addition to trapping, the PowerPC architecture allows compilers to detect any exceptions including underflow by using a slightly different opcode then a conditional branch. If trapping on exceptions was already turned on then doing it this way requires turning it off for the duration.</font><br>
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<font size="2" face="sans-serif">- Ian McIntosh IBM Canada Lab Compiler Back End Support and Development<br>
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<img width="16" height="16" src="cid:1__=0ABBF67EDFFD5DDC8f9e8a93df938@ca.ibm.com" border="0" alt="Inactive hide details for Jim Thomas ---2014-06-04 03:33:20 PM---So 754-2008 does not explicitly recommendation a means to dete"><font size="2" color="#424282" face="sans-serif">Jim Thomas ---2014-06-04 03:33:20 PM---So 754-2008 does not explicitly recommendation a means to detect underflow exceptions, but its recom</font><br>
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<font size="1" face="sans-serif">Jim Thomas <jaswthomas@sbcglobal.net></font></td></tr>
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<font size="1" face="sans-serif">CFP <cfp-interest@ucbtest.org>, </font></td></tr>
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<font size="1" face="sans-serif">2014-06-04 03:33 PM</font></td></tr>
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<ul style="padding-left: 4pt"><font size="1" color="#5F5F5F" face="sans-serif">Subject:</font></ul>
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<font size="1" face="sans-serif">Re: [Cfp-interest] exceptions and flags</font></td></tr>
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<font size="1" face="sans-serif">cfp-interest-bounces@oakapple.net</font></td></tr>
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<tt><font size="2">So 754-2008 does not explicitly recommendation a means to detect underflow exceptions, but its recommendation that languages provide alternate exception handling entails detecting underflow exceptions. Maybe Part 5 could leave detection of tiny exact underflow cases as a recommended option, which would allow the simpler slower implementation using flags.<br>
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-Jim<br>
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On Jun 3, 2014, at 9:32 PM, David Hough CFP <pcfp@oakapple.net> wrote:<br>
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>> Does all HW provide a way for SW to detect an underflow exception?<br>
> <br>
> The only way I know is to enable the underflow trap. If the trap works<br>
> as recommended by 754-1985, then that suffices.<br>
> <br>
> But 754-1985 chapter 8 only recommends traps (to implementations) while<br>
> 754-2008 chapter 8 only recommends alternate exception handling (to languages).<br>
> Alternate exception handling replaces traps as far as programming environments<br>
> go, but the traps are still a very likely implementation mechanism.<br>
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