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April 06, 2009 [Issue 2809] New: Wrong code for unsigned shift | ||||
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http://d.puremagic.com/issues/show_bug.cgi?id=2809 Summary: Wrong code for unsigned shift Product: D Version: 2.027 Platform: PC URL: http://www.digitalmars.com/webnews/newsgroups.php?art_gr oup=digitalmars.D.learn&article_id=16107 OS/Version: Windows Status: NEW Keywords: wrong-code Severity: normal Priority: P2 Component: DMD AssignedTo: bugzilla@digitalmars.com ReportedBy: maxmo@pochta.ru --- const short s=-1; static assert(s>>>1==0x7fff); //fail --- Influenced by error messages, where compiler transforms a>>>b to cast(int)a>>>b. Here compiler complains about conversion to return type: --- short a(short b) { return b>>>1; } --- When you add it, the code is accepted, but the bug is already triggered. --- short a(short b) { return cast(short)(b>>>1); } --- -- |
January 17, 2010 [Issue 2809] Wrong constant folding for unsigned shift | ||||
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Posted in reply to d-bugmail | http://d.puremagic.com/issues/show_bug.cgi?id=2809 Don <clugdbug@yahoo.com.au> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |clugdbug@yahoo.com.au Version|2.027 |1.00 Summary|Wrong code for unsigned |Wrong constant folding for |shift |unsigned shift --- Comment #1 from Don <clugdbug@yahoo.com.au> 2010-01-16 23:37:20 PST --- Also applies to D1. Seems to be a constant folding issue. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- |
January 17, 2010 [Issue 2809] Wrong constant folding for unsigned shift | ||||
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Posted in reply to d-bugmail | http://d.puremagic.com/issues/show_bug.cgi?id=2809 Don <clugdbug@yahoo.com.au> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |patch --- Comment #2 from Don <clugdbug@yahoo.com.au> 2010-01-17 11:48:08 PST --- Now I'm really confused. In Walter's test suite, this case is explicitly tested! static assert((cast(short)-1 >>> 1) == int.max); There's a wrong statement in the bug description. "Here compiler complains about conversion to return type: --- short a(short b) { return b>>>1; } " the response to this should be: short a(short b) { return b>>>cast(short)1; } So I'm rather confused about whether this is a bug, or intended (but unintuitive) behaviour. If it's a bug, it can be fixed by modifying UshrExp::semantic(Scope *sc) in expression.c (around line 10103): e1 = e1->checkIntegral(); e2 = e2->checkIntegral(); - e1 = e1->integralPromotions(sc); + e = e1->integralPromotions(sc); e2 = e2->castTo(sc, Type::tshiftcnt); - type = e1->type; + type = e->type; } return this; and in constfold.c Ushr(), around line 600, removing two asserts. case Tint8: case Tuns8: - assert(0); // no way to trigger this value = (value & 0xFF) >> count; break; case Tint16: case Tuns16: - assert(0); // no way to trigger this value = (value & 0xFFFF) >> count; break; -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- |
November 15, 2010 [Issue 2809] Wrong constant folding for unsigned shift | ||||
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Posted in reply to d-bugmail | http://d.puremagic.com/issues/show_bug.cgi?id=2809 simon <s.d.hammett@googlemail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |s.d.hammett@googlemail.com --- Comment #3 from simon <s.d.hammett@googlemail.com> 2010-11-15 14:29:19 PST --- Mr Bs test case is wrong: static assert((cast(short)-1 >>> 1) == int.max); should be: static assert((cast(short)-1 >>> 1) == short.max); unsigned right shift is perfectly well defined, though giving it it's own operator seems like overkill. I think it would be better as a function in std.intrinsic. You aren't going to use unsigned shift unless you know what you doing and care about performance. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- |
November 15, 2010 [Issue 2809] Wrong constant folding for unsigned shift | ||||
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Posted in reply to d-bugmail | http://d.puremagic.com/issues/show_bug.cgi?id=2809 --- Comment #4 from Don <clugdbug@yahoo.com.au> 2010-11-15 15:06:34 PST --- (In reply to comment #3) > Mr Bs test case is wrong: > > static assert((cast(short)-1 >>> 1) == int.max); > > should be: > > static assert((cast(short)-1 >>> 1) == short.max); Not so. You might be thinking of this, which _is_ true: static assert((cast(short)-1 >>> cast(short)1) == short.max); The problem is that >>> interacts badly with implicit type conversions. With every other operator, typeof(short OP int) == int. Possible solutions are: (a) special case for >>> (b) disallow >>> for types smaller than int (c) drop it from the language Personally I think (c) is the only option that makes sense. > unsigned right shift is perfectly well defined, > though giving it it's own operator seems like overkill. > > I think it would be better as a function in std.intrinsic. You don't need it at all. Just cast to unsigned, then >>. >>> is a ridiculous operator. > You aren't going to use unsigned shift unless you know what you doing and care about performance. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- |
November 16, 2010 [Issue 2809] Wrong constant folding for unsigned shift | ||||
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Posted in reply to d-bugmail | http://d.puremagic.com/issues/show_bug.cgi?id=2809 --- Comment #5 from Sobirari Muhomori <dfj1esp02@sneakemail.com> 2010-11-16 11:53:02 PST --- >short a(short b) { return b>>>cast(short)1; } Shouldn't number literals work as smallest possible type and promoted as needed? Like here: --- byte a=1; --- -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- |
November 16, 2010 [Issue 2809] Wrong constant folding for unsigned shift | ||||
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Posted in reply to d-bugmail | http://d.puremagic.com/issues/show_bug.cgi?id=2809 --- Comment #6 from Sobirari Muhomori <dfj1esp02@sneakemail.com> 2010-11-16 11:59:34 PST --- Number literals are polysemous, right? So binary ops should work like this: opBinary(l,r) { if(is(typeof(r)==polysemous)) { opBinary(l,implicit_cast(typeof(l))r); } } or something like that. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- |
November 16, 2010 [Issue 2809] Wrong constant folding for unsigned shift | ||||
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Posted in reply to d-bugmail | http://d.puremagic.com/issues/show_bug.cgi?id=2809 --- Comment #7 from Sobirari Muhomori <dfj1esp02@sneakemail.com> 2010-11-16 12:34:12 PST --- > You don't need it at all. Just cast to unsigned, then >>. > >>> is a ridiculous operator. See bug 5225. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- |
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