[Issue 14958] Casting a double to ulong sometimes produces wrong results

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=14958

yebblies <yebblies at gmail.com> changed:

           What    |Removed                     |Added
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             Status|REOPENED                    |RESOLVED
                 CC|                            |yebblies at gmail.com
         Resolution|---                         |INVALID

--- Comment #3 from yebblies <yebblies at gmail.com> ---
This is working to spec.  Please re-open as an enhancement request if you feel
it's necessary.

The way it goes, is that floating-point hardware does not give us the
guarantees you want.  E.g. a 32-bit multiply-and-add instruction might use 36
bit precision internally.

Given this, we have two choices:
1. Avoid floating-point hardware
2. Allow intermediates to use higher precision than operands

1 comes with an obvious performance penalty.
2 causes some confusion.

DMD calculates everything at 80-bit precision at compile time, and the spec
allows it.

Identical floating point calculations can also produce different results thanks
to differing levels of inlining and exact register allocation.

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