Re: Interval Arithmetic

[ponce via Digitalmars-d-learn]

On Thursday, 1 October 2015 at 21:13:30 UTC, Marco Leise wrote:


Nice to have in Phobos. I assume you have to set the correct 
control word depending on whether you perform math on the FPU 
or via SSE (as is standard for x86_64)? And I assume further 
that DMD always uses FPU math and other compilers provide flags 
to switch between FPU and SSE?


I don't know which compiler use which. On x86_64, a compiler is 
in practice free to mix-and-match FPU and SSE, the instructions 
are still there and working.

Re: Interval Arithmetic

[Marco Leise via Digitalmars-d-learn]

Am Tue, 29 Sep 2015 21:04:00 +
schrieb Wulfrick <arm.p...@gmail.com>:

> Is there an interval arithmetic library in D? I couldn’t find one.
> 
> In case I had to write my own, I understand that the IEEE 
> standard floating point arithmetic provides operations for 
> rounding up or down certain operations like summing, subtracting, 
> etc. (thus overriding the default behavior of rounding to nearest 
> representable).
> 
> How do I access this functionality in D? At first I thought that 
> std.math.nextDown and nextUp is what I needed, but not so. 
> Apparently these functions return the previous or next 
> representable *after* the calculation has been done.
> 
> For example, I would like the value of x+y rounded in the 
> arithmetic towards -\infty, which may or may not be nextDown(x+y).
> 
> Any luck?
> Thanks for reading!

Yes, Phobos provides you with this thing:
http://dlang.org/phobos/std_math.html#.FloatingPointControl
Read the help carefully. End of the scope generally means "}".

You can also use the C standard library from D and use:
http://www.cplusplus.com/reference/cfenv/fesetround/

  import core.stdc.fenv;
  fesetround( FE_DOWNWARD );
  auto z = x + y;

And if all that still isn't enough you can write it in inline
assembler using the `fldcw` mnemonic.

Note that the FP control word is per thread and any external
code you call or even buggy interrupt handlers could change or
reset it to defaults. Known cases include a faulty printer
driver and Delphi's runtime, which enables FP exceptions to
throw exceptions on division by 0. Just saying this so if it
ever happens you have it in the back of your mind. Against
interrupt handlers you probably cannot protect, but when
calling other people's code it would be best not depend on
what the FP control word is set to on return.
`FloatingPointControl` is nice here, because you can
temporarily set the rounding mode directly for a block of FP
instructions where no external libraries are involved.

-- 
Marco

Re: Interval Arithmetic

[ponce via Digitalmars-d-learn]

On Thursday, 1 October 2015 at 11:40:28 UTC, Marco Leise wrote:


Note that the FP control word is per thread and any external 
code you call or even buggy interrupt handlers could change or 
reset it to defaults. Known cases include a faulty printer 
driver and Delphi's runtime, which enables FP exceptions to 
throw exceptions on division by 0. Just saying this so if it 
ever happens you have it in the back of your mind. Against 
interrupt handlers you probably cannot protect, but when 
calling other people's code it would be best not depend on what 
the FP control word is set to on return. `FloatingPointControl` 
is nice here, because you can temporarily set the rounding mode 
directly for a block of FP instructions where no external 
libraries are involved.


I have a RAII struct to save/restore the FP control word.
It also handle the SSE control word which unfortunately exist.

https://github.com/p0nce/dplug/blob/master/plugin/dplug/plugin/fpcontrol.d

Re: Interval Arithmetic

[Marco Leise via Digitalmars-d-learn]

Am Thu, 01 Oct 2015 12:03:10 +
schrieb ponce :

> I have a RAII struct to save/restore the FP control word.
> It also handle the SSE control word which unfortunately exist.
> 
> https://github.com/p0nce/dplug/blob/master/plugin/dplug/plugin/fpcontrol.d

Nice to have in Phobos. I assume you have to set the correct
control word depending on whether you perform math on the FPU
or via SSE (as is standard for x86_64)? And I assume further
that DMD always uses FPU math and other compilers provide
flags to switch between FPU and SSE?

-- 
Marco

Re: Interval Arithmetic

[anonymous via Digitalmars-d-learn]

On Tuesday, 29 September 2015 at 21:04:06 UTC, Wulfrick wrote:
Is there an interval arithmetic library in D? I couldn’t find 
one.

None I am aware of.


In case I had to write my own, I understand that the IEEE 
standard floating point arithmetic provides operations for 
rounding up or down certain operations like summing, 
subtracting, etc. (thus overriding the default behavior of 
rounding to nearest representable).


How do I access this functionality in D? At first I thought 
that std.math.nextDown and nextUp is what I needed, but not so. 
Apparently these functions return the previous or next 
representable *after* the calculation has been done.


For example, I would like the value of x+y rounded in the 
arithmetic towards -\infty, which may or may not be 
nextDown(x+y).


Any luck?
Thanks for reading!


fencv.h  [1] + a few extern(C) declarations could work - changes 
the rounding mode.

Maybe there is an inline ASM solution, too.

I have never tried to use that from D. The FENV_ACCESS pragma 
could cause problems - don't know how to pass that info to a D 
compiler (never tried to figure it out).


It may be easier to generate an binding for an existing C/C++ 
lib, e.g. [2] (page is in German, but the downloadable tar.gz 
("komprimierte (gzipped) tar-Datei") contains an English readme. 
Boost also contains an interval arithmetic lib [3], but the use 
of C++ templates will most likely force you to write some glue 
code in C++...



[1] http://www.cplusplus.com/reference/cfenv/
[2] http://www.ti3.tuhh.de/keil/profil/ (GPL)
[3] 
http://www.boost.org/doc/libs/1_58_0/libs/numeric/interval/doc/interval.htm

Interval Arithmetic

[Wulfrick via Digitalmars-d-learn]

Is there an interval arithmetic library in D? I couldn’t find one.

In case I had to write my own, I understand that the IEEE 
standard floating point arithmetic provides operations for 
rounding up or down certain operations like summing, subtracting, 
etc. (thus overriding the default behavior of rounding to nearest 
representable).


How do I access this functionality in D? At first I thought that 
std.math.nextDown and nextUp is what I needed, but not so. 
Apparently these functions return the previous or next 
representable *after* the calculation has been done.


For example, I would like the value of x+y rounded in the 
arithmetic towards -\infty, which may or may not be nextDown(x+y).


Any luck?
Thanks for reading!