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From: "npr1 at suomi24 dot fi" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/16607] Incorrect FP code generated in member data initialization Date: Mon, 19 Jul 2004 14:40:00 -0000 [thread overview] Message-ID: <20040719143958.30085.qmail@sourceware.org> (raw) In-Reply-To: <20040717172049.16607.npr1@suomi24.fi> ------- Additional Comments From npr1 at suomi24 dot fi 2004-07-19 14:39 ------- Personally, I don't mind floats being imprecise in the last few bits, or doubles being imprecise in their last few bits. What I do mind is that after assigning float * float to double, that double value can have "simultaneously" two values that differ in almost half of their last bits. If this is allowed, one can never count on double having any more practical precision than float, especially with the duality being carried over [inlined] function calls. I'm sure many programs rely on this but, since it's broken so rarely it's not noticed until with a new compiler or a small non-related change in code structure. (Ouch!) The "double = float * float" case could be fixed without performance issues, too. The compiler could well generate code that always uses the value with extra precision (that of double, or more). As I noted, the compiler already does this in all cases but the one. At least in my example, using two forms (single and double precision) of the result generates an unnecessary instruction, so actually there would be a performance increase. I suppose a compiler patch could be too laborious compared to the gains, especially as it mustn't affect non-x86 compilations. My personal fix will be converting all uses of float to double, but obviously this is not good for all programs. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16607
prev parent reply other threads:[~2004-07-19 14:40 UTC|newest] Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2004-07-17 17:20 [Bug c++/16607] New: " npr1 at suomi24 dot fi 2004-07-17 17:40 ` [Bug c++/16607] " pinskia at gcc dot gnu dot org 2004-07-17 20:41 ` npr1 at suomi24 dot fi 2004-07-17 22:29 ` pinskia at gcc dot gnu dot org 2004-07-18 0:38 ` npr1 at suomi24 dot fi 2004-07-19 2:01 ` npr1 at suomi24 dot fi 2004-07-19 2:58 ` npr1 at suomi24 dot fi 2004-07-19 3:22 ` zack at gcc dot gnu dot org 2004-07-19 14:40 ` npr1 at suomi24 dot fi [this message]
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