* Re: [gfortran] Exponentiation by integral exponents
[not found] <20040429024944.52618.qmail@web15212.mail.bjs.yahoo.com>
@ 2004-04-29 12:20 ` Tobias Schlüter
2004-04-29 15:50 ` Are BUILT_IN_POWII and BUILT_IN_POWCI necessary? (RE: Exponentiation by integral exponents) Feng Wang
0 siblings, 1 reply; 7+ messages in thread
From: Tobias Schlüter @ 2004-04-29 12:20 UTC (permalink / raw)
To: Feng Wang; +Cc: fortran, gcc
[ forwarding to gcc@gcc.gnu.org so more knowledgeable people can comment
on the point I make in the last paragraph ]
Feng Wang wrote:
> Hi, Tobi, Paul, etc
> I missed the discussion because of my poor modem. But I have implemented this
> and the patch is under test. IMHO, we have to implement the algorithm described
> by Knuth in the FE. BUILT_IN_POW only deals with Real type. How about complex
> type? There are also many problems to consider when an integer is raised to an
> negative integer. The result is just 0, -1, or 1. So it is not correct to
> convert integer to real.
This is a good point that I hadn't thought about.
> I think we should also implement the runtime library
> function powi. When a value is raised to an varible integer, we just call the
> library function. The value may be of integer type, real type or complex type.
Yeah, I thought so as well. I was already looking for an implementation.
> I have done these and in a few days I will give the patch. I didn't port Andy's
> implementation. Andy's vertion only deal with exponent under 100 and don't
> consider (integer ** negative integer). The main algorithm in my implementation
> is from builtins.c and can deal with an arbitrary integer exponent. The
> algorithm in powi library function is from libf77.
If your patch is finished I agree that we should go with your patch, as
mine is far from finished. I chose to port Andy's implementation as this
was my first step in GCC trees, and I didn't want to do something from
scratch :-)
I don't necessarily agree that this should be handled in the FE, though.
There might be other languages that have an "integral exponent" idiom,
so a language independent solution might be preferable.
- Tobi
^ permalink raw reply [flat|nested] 7+ messages in thread
* Are BUILT_IN_POWII and BUILT_IN_POWCI necessary? (RE: Exponentiation by integral exponents)
2004-04-29 12:20 ` [gfortran] Exponentiation by integral exponents Tobias Schlüter
@ 2004-04-29 15:50 ` Feng Wang
0 siblings, 0 replies; 7+ messages in thread
From: Feng Wang @ 2004-04-29 15:50 UTC (permalink / raw)
To: Tobias_Schlüter; +Cc: fortran, gcc
[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset=gb2312, Size: 2443 bytes --]
--- Tobias_Schlüter <tobias.schlueter@physik.uni-muenchen.de> µÄÕýÎÄ£º> [
forwarding to gcc@gcc.gnu.org so more knowledgeable people can comment
> on the point I make in the last paragraph ]
>
> Feng Wang wrote:
> > Hi, Tobi, Paul, etc
> > I missed the discussion because of my poor modem. But I have implemented
> this
> > and the patch is under test. IMHO, we have to implement the algorithm
> described
> > by Knuth in the FE. BUILT_IN_POW only deals with Real type. How about
> complex
> > type? There are also many problems to consider when an integer is raised to
> an
> > negative integer. The result is just 0, -1, or 1. So it is not correct to
> > convert integer to real.
>
> This is a good point that I hadn't thought about.
>
> > I think we should also implement the runtime library
> > function powi. When a value is raised to an varible integer, we just call
> the
> > library function. The value may be of integer type, real type or complex
> type.
>
> Yeah, I thought so as well. I was already looking for an implementation.
>
> > I have done these and in a few days I will give the patch. I didn't port
> Andy's
> > implementation. Andy's vertion only deal with exponent under 100 and don't
> > consider (integer ** negative integer). The main algorithm in my
> implementation
> > is from builtins.c and can deal with an arbitrary integer exponent. The
> > algorithm in powi library function is from libf77.
>
> If your patch is finished I agree that we should go with your patch, as
> mine is far from finished. I chose to port Andy's implementation as this
> was my first step in GCC trees, and I didn't want to do something from
> scratch :-)
>
> I don't necessarily agree that this should be handled in the FE, though.
> There might be other languages that have an "integral exponent" idiom,
> so a language independent solution might be preferable.
To this point it is reasonable. But thus we will have to build and expand
BUILT_IN_POWII (int ** int) and BUILT_IN_POWCI (complex ** int) in the BE. Is
this necessary? Maybe the GCC community can give us some suggestion.
Feng Wang
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^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [gfortran] Exponentiation by integral exponents
2004-04-28 3:05 ` Paul Brook
@ 2004-04-28 3:48 ` Tobias Schlüter
0 siblings, 0 replies; 7+ messages in thread
From: Tobias Schlüter @ 2004-04-28 3:48 UTC (permalink / raw)
To: Paul Brook; +Cc: fortran, Andrew Pinski, gcc@gcc.gnu.org list
Paul Brook wrote:
> On Tuesday 27 April 2004 23:07, Tobias Schlüter wrote:
>
>>Andrew Pinski wrote:
>>
>>>On Apr 27, 2004, at 17:14, Tobias Schlüter wrote:
>>>
>>>>FYI I have ported Andy's code for exponentiation by an integral
>>>>exponent to our tree. This is an implementation of Knuth's algorithm
>>
>>...
>>
>>
>>>You should not need it if you use __builtin_pow and you turn on
>>>flag_unsafe_math_optimizations on. Maybe the best way is to have
>>>another flag
>>>to say expand __builtin_pow always.
>>
>>Does the builtin recognize the case pow(x,(float)i), where i is an
>>integer? Then this sounds like a very good idea.
>
>
> Maybe the way to indicate we always want to expand __builtin_pow would be to
> pass the second parameter with an integer type. It may be easier to add
> __builtin_powi to avoid needing polymorphic builtins.
Definitely.
Anyway, I tried to implement Andrew's suggestion as a quick'n'dirty
hack. Right now I get an ICE. What is the correct way to generate the
equivalent of a typecast in C?
What I tried was this: gfc_conv_power_op has this code:
type = TREE_TYPE (lse.expr);
kind = expr->op1->ts.kind;
switch (expr->op2->ts.type)
{
case BT_INTEGER:
/* Integer powers are expanded inline as multiplications. */
gfc_conv_integer_power (se, lse.expr, rse.expr);
return;
Instead of calling gfc_integer_power and returning, I want to convert
rse.expr to the type of lse.expr. So I tried both of the following
(gfc_conv_expr_type has no explanatory comment, so I'm just guessing
that this might be the function I'm looking for):
gfc_conv_expr_type (&rse, expr->op2, type); // first try
rse.expr = convert (type, rse.expr); // second try
After that I select the function based on the type of lse.expr as in the
real case and continue as if rse.expr had not been int all the time.
What am I missing? I'm still within my first three hours of messing with
gcc trees, so I might well be missing the obvious.
- Tobi
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [gfortran] Exponentiation by integral exponents
2004-04-28 1:38 ` Tobias Schlüter
2004-04-28 2:56 ` Andrew Pinski
@ 2004-04-28 3:05 ` Paul Brook
2004-04-28 3:48 ` Tobias Schlüter
1 sibling, 1 reply; 7+ messages in thread
From: Paul Brook @ 2004-04-28 3:05 UTC (permalink / raw)
To: fortran; +Cc: Tobias Schlüter, Andrew Pinski, gcc@gcc.gnu.org list
On Tuesday 27 April 2004 23:07, Tobias Schlüter wrote:
> Andrew Pinski wrote:
> > On Apr 27, 2004, at 17:14, Tobias Schlüter wrote:
> >> FYI I have ported Andy's code for exponentiation by an integral
> >> exponent to our tree. This is an implementation of Knuth's algorithm
>
> ...
>
> > You should not need it if you use __builtin_pow and you turn on
> > flag_unsafe_math_optimizations on. Maybe the best way is to have
> > another flag
> > to say expand __builtin_pow always.
>
> Does the builtin recognize the case pow(x,(float)i), where i is an
> integer? Then this sounds like a very good idea.
Maybe the way to indicate we always want to expand __builtin_pow would be to
pass the second parameter with an integer type. It may be easier to add
__builtin_powi to avoid needing polymorphic builtins.
Paul
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [gfortran] Exponentiation by integral exponents
2004-04-28 1:38 ` Tobias Schlüter
@ 2004-04-28 2:56 ` Andrew Pinski
2004-04-28 3:05 ` Paul Brook
1 sibling, 0 replies; 7+ messages in thread
From: Andrew Pinski @ 2004-04-28 2:56 UTC (permalink / raw)
To: Tobias Schlüter
Cc: GCC Fortran mailing list, gcc@gcc.gnu.org list, Andrew Pinski
On Apr 27, 2004, at 18:07, Tobias Schlüter wrote:
> Andrew Pinski wrote:
>> On Apr 27, 2004, at 17:14, Tobias Schlüter wrote:
>>>
>>> FYI I have ported Andy's code for exponentiation by an integral
>>> exponent to our tree. This is an implementation of Knuth's algorithm
> ...
>> You should not need it if you use __builtin_pow and you turn on
>> flag_unsafe_math_optimizations on. Maybe the best way is to have
>> another flag
>> to say expand __builtin_pow always.
>
> Does the builtin recognize the case pow(x,(float)i), where i is an
> integer? Then this sounds like a very good idea.
Yes it does except that flag_unsafe_math_optimizations has to be true
but we can
easily change that.
Thanks,
Andrew Pinski
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [gfortran] Exponentiation by integral exponents
2004-04-27 23:09 ` [gfortran] Exponentiation by integral exponents Andrew Pinski
@ 2004-04-28 1:38 ` Tobias Schlüter
2004-04-28 2:56 ` Andrew Pinski
2004-04-28 3:05 ` Paul Brook
0 siblings, 2 replies; 7+ messages in thread
From: Tobias Schlüter @ 2004-04-28 1:38 UTC (permalink / raw)
To: Andrew Pinski; +Cc: GCC Fortran mailing list, gcc@gcc.gnu.org list
Andrew Pinski wrote:
>
> On Apr 27, 2004, at 17:14, Tobias Schlüter wrote:
>
>>
>> FYI I have ported Andy's code for exponentiation by an integral
>> exponent to our tree. This is an implementation of Knuth's algorithm
...
>
> You should not need it if you use __builtin_pow and you turn on
> flag_unsafe_math_optimizations on. Maybe the best way is to have
> another flag
> to say expand __builtin_pow always.
>
Does the builtin recognize the case pow(x,(float)i), where i is an
integer? Then this sounds like a very good idea.
- Tobi
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [gfortran] Exponentiation by integral exponents
[not found] <408ECD52.2090709@physik.uni-muenchen.de>
@ 2004-04-27 23:09 ` Andrew Pinski
2004-04-28 1:38 ` Tobias Schlüter
0 siblings, 1 reply; 7+ messages in thread
From: Andrew Pinski @ 2004-04-27 23:09 UTC (permalink / raw)
To: Tobias Schlüter
Cc: GCC Fortran mailing list, gcc@gcc.gnu.org list, Andrew Pinski
On Apr 27, 2004, at 17:14, Tobias Schlüter wrote:
>
> FYI I have ported Andy's code for exponentiation by an integral
> exponent to our tree. This is an implementation of Knuth's algorithm
> which uses the minimum number of multiplications for exponents < 100.
> As an additional bonus there's no more need to special case an
> exponent of three, the optimal code is generated automatically. I'll
> submit this once my copyright assignment is handled.
>
> Does anybody have any insight on how to write testcases for this?
You should not need it if you use __builtin_pow and you turn on
flag_unsafe_math_optimizations on. Maybe the best way is to have
another flag
to say expand __builtin_pow always.
Thanks,
Andrew Pinski
^ permalink raw reply [flat|nested] 7+ messages in thread
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2004-04-29 12:20 ` [gfortran] Exponentiation by integral exponents Tobias Schlüter
2004-04-29 15:50 ` Are BUILT_IN_POWII and BUILT_IN_POWCI necessary? (RE: Exponentiation by integral exponents) Feng Wang
[not found] <408ECD52.2090709@physik.uni-muenchen.de>
2004-04-27 23:09 ` [gfortran] Exponentiation by integral exponents Andrew Pinski
2004-04-28 1:38 ` Tobias Schlüter
2004-04-28 2:56 ` Andrew Pinski
2004-04-28 3:05 ` Paul Brook
2004-04-28 3:48 ` Tobias Schlüter
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