[Issue 3171] % not implemented correctly for floats
https://issues.dlang.org/show_bug.cgi?id=3171 Andrei Alexandrescu and...@erdani.com changed: What|Removed |Added Version|unspecified |D2 --
[Issue 3171] % not implemented correctly for floats
http://d.puremagic.com/issues/show_bug.cgi?id=3171 Walter Bright bugzi...@digitalmars.com changed: What|Removed |Added Status|NEW |RESOLVED Resolution||FIXED --- Comment #6 from Walter Bright bugzi...@digitalmars.com 2009-12-06 00:46:11 PST --- Fixed dmd 1.053 and 2.037 -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email --- You are receiving this mail because: ---
[Issue 3171] % not implemented correctly for floats
http://d.puremagic.com/issues/show_bug.cgi?id=3171 Don clugd...@yahoo.com.au changed: What|Removed |Added CC||clugd...@yahoo.com.au --- Comment #2 from Don clugd...@yahoo.com.au 2009-07-14 01:49:30 PDT --- (In reply to comment #1) As to why the code generator doesn't use FPREM1 instead of FPREM, there's the following comment: We don't use fprem1 because for some inexplicable reason we get -5 when we do _modulo(15, 10) This could be a bug in older CPUs. It isn't a bug. That's what the IEEE remainder specifies. Note that C's fmod is NOT the same as IEEE remainder. 15/10 = 1.5, so there's a choice of n == 1 or n==2. The standard specifies even n in such cases, so r == a - b*n == 15 - 2*10 == -5. That's kind of... weird, highly non-intuitive, and not terribly useful. I'm pretty sure that that behaviour would be unpopular. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email --- You are receiving this mail because: ---
[Issue 3171] % not implemented correctly for floats
http://d.puremagic.com/issues/show_bug.cgi?id=3171 --- Comment #4 from Don clugd...@yahoo.com.au 2009-07-14 04:03:19 PDT --- (In reply to comment #3) Thanks for the explanation. At least I know why that happens, now. What do you suggest, then? Staying with FPREM or going with FPREM1 ? It's hard to justify including a primitive built-in operator that differs from IEEE. But it may be justifiable when it's the only way to avoid a major break from C and intuition. int x = 15 % 10; int y = cast(int)((cast(float)15) % 10); // Are we really comfortable with these being completely different? You know, all this time I was thinking that the behaviour of % for negative integers was because it needed to be consistent with floating-point modulus... Now it just seems to be wrong. But I think I have the answer. In IEEE, the preferred conversion from float to int uses round-to-nearest. IEEE remainder makes sense in that context. Since in cast(int), D has inherited 'chop' rounding from C, D needs to also inherit C's fmod behaviour. So D should stay with FPREM. But we need to document it properly. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email --- You are receiving this mail because: ---
