<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>If the type were INTEGER instead of CARDINAL then the current implementation *does* allow wrap-around. I've fixed the range check so that overflow does not permit the bits for FIRST(INTEGER) to be stored in the CARDINAL.</div><div><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; 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: 0; "><span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -webkit-text-decorations-in-effect: none; text-indent: 0px; -webkit-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -webkit-text-decorations-in-effect: none; text-indent: 0px; -webkit-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -webkit-text-decorations-in-effect: none; text-indent: 0px; -webkit-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -webkit-text-decorations-in-effect: none; text-indent: 0px; -webkit-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -webkit-text-decorations-in-effect: none; text-indent: 0px; -webkit-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -webkit-text-decorations-in-effect: none; text-indent: 0px; -webkit-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -webkit-text-decorations-in-effect: none; text-indent: 0px; -webkit-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -webkit-text-decorations-in-effect: none; text-indent: 0px; -webkit-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -webkit-text-decorations-in-effect: none; text-indent: 0px; -webkit-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><div><font class="Apple-style-span" color="#0000FF" face="'Gill Sans'"><span class="Apple-style-span" style="font-size: medium;"><br></span></font></div></span></span></span></span></span></span></span></span></div></span></span></div><div><div>On 11 Jan 2010, at 19:25, Rodney M. Bates wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>If the type were INTEGER instead of cardinal, (and assuming no checking for overflows),<br>I think wrapping around to the maximal negative value would be reasonable. Even for<br>CARDINAL, it's reasonable for the arithmetic operation itself (which is really being<br>done in the full INTEGER range). But then the assignment of the result back to the<br>CARDINAL variable really must do a range check. This derives from the assignment<br>x:= ... in the WITH equivalent, not from the + 1 operation.<br><br>Mainly, there is a pervasive principle in the safety of the language that you can<br>never get a bit pattern stored in a variable that does not map back to an abstract<br>value of its type. We really need to preserve this.<br><br>Tony Hosking wrote:<br><blockquote type="cite">Even under the interpretation for INC that yields:<br></blockquote><blockquote type="cite">VAR s: CARDINAL := LAST(INTEGER);<br></blockquote><blockquote type="cite">BEGIN WITH x = s DO x := VAL(ORD(x) + 1, CARDINAL) END; END;<br></blockquote><blockquote type="cite">the compiler currently does not insert a bounds check, because it reasons that the bound for ORD(x) + 1 is [0+1, LAST(INTEGER)], so the result is always assignable to CARDINAL.<br></blockquote><blockquote type="cite">In reality, the compiler should presumably assume that because ORD(x) + 1 might overflow if ORD(x) = LAST(INTEGER) then the bound for the expression ORD(x)+1 is actually the same as INTEGER: [FIRST(INTEGER),LAST(INTEGER)]. So, because this is larger than the range for CARDINAL it really needs to insert a bounds check on the conversion to CARDINAL.<br></blockquote><blockquote type="cite">On 9 Jan 2010, at 23:33, Tony Hosking wrote:<br></blockquote><blockquote type="cite"><blockquote type="cite">So, in my experiments with range checking on integers, I have been playing with the overflow case:<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">VAR s: CARDINAL := LAST(INTEGER);<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">BEGIN INC(s) END;<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">Should this fail at runtime with a range check error?<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">The language definition says that integer overflow may or may not be checked, depending on the implementation. (See FloatMode.i3).<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">If it is not checked, is it reasonable that s takes on the value FIRST(INTEGER)?<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">Antony Hosking | Associate Professor | Computer Science | Purdue University<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">305 N. University Street | West Lafayette | IN 47907 | USA<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">Office +1 765 494 6001 | Mobile +1 765 427 5484<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote></div></blockquote></div><br></body></html>