[Issue 20759] Invalid printf checks for long double on win64

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20759

kinke <kinke at gmx.net> changed:

           What    |Removed                     |Added
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                 CC|                            |kinke at gmx.net

--- Comment #1 from kinke <kinke at gmx.net> ---
This is specific to DMD and should be an issue with -m32mscoff too. As you
said, the MSVC `long double` type is a (for C++, differently mangled than
double) 64-bit double (IIRC, Microsoft outright forbids X87 usage in kernel
code), while DMD goes with 80-bit X87 reals for those targets (so printf and
scanf etc. from the MS runtime cannot be used without converting to lower
precision first). LDC uses 64-bit reals for MSVC targets, so this works.

The deprecation wrt. double is IMO valid, as `%Lg` with a double isn't portable
and just happens to work for targets with 64-bit reals, but this deprecation
should IMO be host-agnostic, i.e., not suddenly popping up when targeting
AArch64 or Posix x86.

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