<html><head><base href="x-msg://1648/"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><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; 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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><span class="Apple-style-span" style="font-size: medium; ">On 12 Jan 2010, at 04:23, Jay K wrote:</span></div></span></span></span></span></span></span></span></span></div></span></span></div><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; ">I propose that integer signed overflow always raise an immediate exception.<br>Word.T should either raise an exception for unsigned overflow, or maybe no exceptions at all.<br>For folks that want silent wraparound, maybe a separate interface like UnsafeInt.<br></div></span></blockquote><div><br></div><div>That is going to pose a performance issue (that many C programmers may baulk at!).</div><br><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; ">I propose that FloatMode's integer features not be the way forward.<br></div></span></blockquote><div><br></div><div>Why not?</div><br><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; ">There are two implementation strategies.<br> <br> <br> - "check the carry flag"<br> A processor-specific thing, but possibly something easy for the gcc backend to do.<br> And very likely easy for the integrated backend.<br> Probably very efficient.<br></div></span></blockquote><div><br></div><div>Yes, doable.</div><br><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; "> - internally generate function calls for every arithmetic operation<br> like how sets are implemented<br></div></span></blockquote><div><br></div><div>Very bad for performance. We should rely on the processor support for arithmetic traps or condition variables.</div><div><br></div><br><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; "> Implementing most such functions is easy enough in portable C.<br> Or maybe using Modula-3 and interface Word.<br></div></span></blockquote><div><br></div><div>Not the best way going forward...</div><div><br></div><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; "> e.g.<br> void add(int a, int b, int* c, int* overflow)<br> {<br> int d = (a + b);<br> /* overflow if input signs are equal and output sign is different;<br> if input signs are unequal, overflow is not possible<br> positive + positive: expect positive, else overflow<br> negative + negative: expect negative, else overflow<br> positive + negative: overflow not possible */<br> *overflow = ((a < 0) == (b < 0) && (d < 0) != (a < 0));<br> *c = d;<br> }<br> <br> <br> void sub(int a, int b, int* c, int* overflow)<br> {<br> int d = (a - b);<br> /* overflow if input signs are unequal and output sign is different than first input;<br> if input signs are equal, overflow is not possible;<br> positive - negative: expect positive, overflow if negative<br> negative - positive: expect negative, overflow if positive<br> positive - positive, negative - negative: overflow not possible */<br> *overflow = ((a < 0) != (b < 0) && (d < 0) != (a < 0));<br> *c = d;<br> }<br> <br>#include <limits.h><br> <br> void mult(int a, int b, int* c, int* overflow)<br> {<br> /* do operation in higher precision and check if it fits */<br> int64 d = (a * (int64)b);<br> *c = (int)d;<br> *overflow = (d >= INT_MIN && d <= INT_MAX);<br> }<br> <br>/* for interface Word */<br> typedef unsigned uint;<br> <br> void addu(uint a, uint b, uint* c, int* overflow)<br> {<br> uint d = (a + b);<br> /* overflow if output less than either input */<br> *overflow = (d < a);<br> *c = d;<br> }<br> <br> void subu(uint a, uint b, uint* c, int* overflow)<br> {<br> uint d = (a - b);<br> /* overflow if output greater than first input */<br> *overflow = (d > a);<br> *c = d;<br> }<br> <br> void multu(uint a, uint b, uint* c, int* overflow)<br> {<br> /* operate at higher precision and see if it fits */<br> uint64 d = (a * (uint64)b);<br> *overflow = (d <= UINT_MAX);<br> *c = (uint)d;<br> }<br> <br> void multLU(uint64 a, uint64 b, uint64* c, int* overflow)<br> {<br> /* break it down into smaller operations, not shown, but not difficult */<br> }<br> <br> <br>Yes I know this is inefficient, but such is a possible price of portable safety.<br> <br> <br>A hybrid is probably possible if the gcc backend support must be processor specific and we gradually provide the implementations.</div></span></blockquote><div><br></div><div>FloatMode seems a perfectly reasonable way forward doesn't it? It allows both trap-based and (with compiler support) checked condition code implementations.</div><br><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; "> <br> <span class="Apple-converted-space"> </span><br> - Jay<br><br><br><br><br><br></div></span></blockquote></div><br></body></html>