On Thursday, 11 May 2017 at 10:22:29 UTC, Dominikus Dittes
Scherkl wrote:
On Thursday, 11 May 2017 at 10:07:32 UTC, Joakim wrote:
On Thursday, 11 May 2017 at 02:05:11 UTC, Nikolay wrote:
I am porting LDC to NetBSD amd64, and I ask advice how to
handle real type. NetBSD has limited support for this type.
What is long double on NetBSD/amd64, 64-bit or full 80-bit?
We were talking about this when I was porting to Android/x86,
where long double is 64-bit but the FPU should support 80-bit.
Iain suggested just sticking to the ABI, ie using 64-bit if
that's how long double is defined (see next three comments
after linked comment):
https://github.com/dlang/phobos/pull/2150#issuecomment-42731651
This type exists, but standard library does not provide full
set of math functions for it (e.g. sinus, cosinus, and etc).
Currently I just forward all function calls to 64 bits
version counterparts, but in this case a set of unit tests
are failing. I see following approaches to handle this issue:
- Totally remove 80 bit real type from NetBSD port (make
real==double)
- Change tests and skip asserts for NetBSD
There is one additional approach: implement these functions
in druntime, but it is too big/massive work for me.
I wouldn't worry about it too much. If someone really needs
this, they will have to chip in. Dmd uses compiler intrinsics
for those trig functions, and I notice that they seem to just
call the native x86 asm instructions:
I hate it if D doesn't fully support the hardware just to be
compatible to some bad designed C library.
This is not just "some... C library," we're talking about the
system ABI here!
Hey, it's a system language! I want to be able to use the
hardware I have to its fullest!
You can: I left real as 80-bit there, but it's irrelevant as
Android/x86 is basically dead since Intel exited the mobile
market.
And for calling C functions you always have to fing the fitting
D-type by checking "mantdig" and map accordingly. Thats really
not so difficult.
The problem is that std.math depends on some basic C math
functions for the native long double type, ie the D "real"
equivalent, and if your system ABI defines long double to be less
precise than what the hardware supports, those more precise math
functions may not exist. Hell, as Nikolay just said, they may
not exist even if your ABI uses the same precision as the
hardware!
In that case, where your platform doesn't provide such precise C
math functions, it's tough for me to care. If you really need
the precision, roll up your sleeves and add it, whether in C or D.
On Thursday, 11 May 2017 at 10:33:21 UTC, Nikolay wrote:
What is long double on NetBSD/amd64, 64-bit or full 80-bit?
80 bit
but function set is not full e.g.
acos supports long double
http://netbsd.gw.com/cgi-bin/man-cgi?acos+3+NetBSD-7.0
cos does not support long double
http://netbsd.gw.com/cgi-bin/man-cgi?cos+3+NetBSD-7.0
In that case, defining real as 80-bit and modifying some tests
for NetBSD seems the way to go. You may want to look at my last
Phobos patch for Android/x86, from a couple years ago:
https://gist.github.com/joakim-noah/5d399fdcd5e484d6aaa2
On Thursday, 11 May 2017 at 10:07:32 UTC, Joakim wrote:
Dmd uses compiler intrinsics for those trig functions, and I
notice that they seem to just call the native x86 asm
instructions:
https://github.com/dlang/dmd/blob/master/src/ddmd/root/longdouble.c#L428
As I know native x87 implementation of many math functions is
terrible, and it is rarely used in real world.
Well, if you don't like what's available and NetBSD doesn't
provide them... up to you to decide where that leads.
