<html><head><base href="x-msg://274/"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">I want to implement the <cstdatomic.h> soon-to-be standard. That is defined as fetch_and_op.<div><br><div>
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"><div><font class="Apple-style-span" color="#0000FF"><font class="Apple-style-span" face="Gill Sans"><span class="Apple-style-span" style="color: rgb(0, 0, 255); font-family: 'Gill Sans'; "><span class="Apple-style-span" style="color: rgb(0, 0, 255); font-family: 'Gill Sans'; ">Antony Hosking</span></span></font></font><font class="Apple-style-span" face="Gill Sans"><span class="Apple-style-span" style="font-family: 'Gill Sans'; "><span class="Apple-style-span" style="font-family: 'Gill Sans'; "><span class="Apple-converted-space"> </span>|<span class="Apple-converted-space"> </span></span></span><span class="Apple-style-span" style="font-family: 'Gill Sans'; "><span class="Apple-style-span" style="font-family: 'Gill Sans'; ">Associate Professor</span></span><span class="Apple-style-span" style="font-family: 'Gill Sans'; "><span class="Apple-style-span" style="font-family: 'Gill Sans'; "> | Computer Science | Purdue University</span></span></font></div><div><font class="Apple-style-span" face="GillSans-Light"><span class="Apple-style-span" style="font-family: GillSans-Light; 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<br><div><div>On 21 Jan 2010, at 08:29, Jay K wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><span class="Apple-style-span" style="border-collapse: separate; font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div class="hmmessage" style="font-size: 10pt; font-family: Verdana; ">(* tmp := Mem [s1.A].t;<br> Mem [s1.A].t := tmp op s0.u;<br> s1.u := tmp; pop *)<br><br><br>Tony, are you sure you want to return the old value, not the new value?<br>That's not great on x86.<br>I believe for "or" and "and", you end up having to do a compare exchange loops.<br> <br> <br>For xor, add, sub, you can compute the old value, ok.<br>But if caller wanted the old value, he can do that himself also.<br>Caller can also write a compare_exchange loop.<br> <br> <br>Therefore, I think it should be:<br> <br>(* tmp := Mem [s1.A].t;<br> Mem [s1.A].t := tmp op s0.u;<br> s1.u := tmp op s0.u; pop *)<br><br>There is of course value in storing the value in mem and stack, since mem<br>can change right away.<br> <br> <br> - Jay<br><br></div></span></blockquote></div><br></div></body></html>