Hi all,
first of all I beg your pardon if this question has been asked
before, but I was unable to find anything in the past posts.
I have written a piece of code that was supposed to be quite portable,
and uses a lot fp numbers. Everything goes well on PPC cpus, but on
some x86 CPU I get a dramatic loss of performance. After some
investigations I've discovered that the problem is caused by some
numbers becoming subnormal, PPC cpus seems to treat them quietly
without any significant loss of speed whereas on some x86 CPU I get
really very poor results as soon as these "strange" entities begin to
pop out...
Does someone know if there is a way to disable subnormal floating
point numbers, maybe using standard c/c++ libs? I don't need them and
for me it will be just ok to have a small quantity dropped to zero -
in fact, the code is written assuming implicitly that very small
number will eventually become zero.
I hope that there is a simple solution for the problem, apart from
reviewing any very single line of code and putting a lot of
if(issubnormal. ..) or whatever else...
Thanx in advance to everybody that can/will help me...
5  3711 
On May 15, 3:27 pm, ultimatewarrior <ultimatecodewa rr...@yahoo.it>
wrote:
first of all I beg your pardon if this question has been asked
before, but I was unable to find anything in the past posts.
I have written a piece of code that was supposed to be quite portable,
and uses a lot fp numbers. Everything goes well on PPC cpus, but on
some x86 CPU I get a dramatic loss of performance. After some
investigations I've discovered that the problem is caused by some
numbers becoming subnormal, PPC cpus seems to treat them quietly
without any significant loss of speed whereas on some x86 CPU I get
really very poor results as soon as these "strange" entities begin to
pop out...
Does someone know if there is a way to disable subnormal floating
point numbers, maybe using standard c/c++ libs? I don't need them and
for me it will be just ok to have a small quantity dropped to zero -
in fact, the code is written assuming implicitly that very small
number will eventually become zero.
I hope that there is a simple solution for the problem, apart from
reviewing any very single line of code and putting a lot of
if(issubnormal. ..) or whatever else...
I don't believe there is anything standard to effect this. I think
you're looking for a compiler switch (e.g., -fn on Sun C++). You
should ask in a group related to your compiler.
Cheers! --M
ultimatewarrior wrote:
Does someone know if there is a way to disable subnormal floating
point numbers, maybe using standard c/c++ libs?
Just assigning the subnormal to a double variable should force it to 0.
---
Walter Bright
Digital Mars C, C++, D programming language compilers
Walter Bright wrote:
ultimatewarrior wrote:
>Does someone know if there is a way to disable subnormal floating
point numbers, maybe using standard c/c++ libs?
Just assigning the subnormal to a double variable should force it to 0.
If the subnormal doesn't propagate, this wouldn't solve the problem,
would it?
Regards,
Zeppe
On 16 Mag, 11:57, Zeppe <zeppe@.remove. all.this.long.c omment.email.it >
wrote:
Walter Bright wrote:
ultimatewarrior wrote:
Does someone know if there is a way to disable subnormal floating
point numbers, maybe using standard c/c++ libs?
Just assigning the subnormal to a double variable should force it to 0.
If the subnormal doesn't propagate, this wouldn't solve the problem,
would it?
Well, I guess no. And I cannot change every bit of code in order to
replace any assignement from float to double.
I've probably found a workaround, anyway, using SSE instead of
standard FPU you can control (through the MXCSR register) how to deal
with subnormal numbers, you can instruct the CPU to treat them as
zeros (exactly what I need), unfortunately you need SSE because the
x87 FPU has no control over this (ok, SSE is there from PIII and
AthlonXP so I think I'll drop support for older CPUs...)
Has someone any experience with issues regarding the use of SSE for
floats (instead of the standard FPU)?
(BTW, thanx for your kind answers!)
"ultimatewarrio r" <ul************ *****@yahoo.itw rote in message
news:11******** **************@ k79g2000hse.goo glegroups.com.. .
Hi all,
first of all I beg your pardon if this question has been asked
before, but I was unable to find anything in the past posts.
I have written a piece of code that was supposed to be quite portable,
and uses a lot fp numbers. Everything goes well on PPC cpus, but on
some x86 CPU I get a dramatic loss of performance. After some
investigations I've discovered that the problem is caused by some
numbers becoming subnormal, PPC cpus seems to treat them quietly
without any significant loss of speed whereas on some x86 CPU I get
really very poor results as soon as these "strange" entities begin to
pop out...
Does someone know if there is a way to disable subnormal floating
point numbers, maybe using standard c/c++ libs? I don't need them and
for me it will be just ok to have a small quantity dropped to zero -
in fact, the code is written assuming implicitly that very small
number will eventually become zero.
I hope that there is a simple solution for the problem, apart from
reviewing any very single line of code and putting a lot of
if(issubnormal. ..) or whatever else...
Thanx in advance to everybody that can/will help me...
Reading other responses, and your responses to their responses, perhaps you
should use double instead of float. My understanding is that double is
faster than float anyway on (most/all) platforms. It also seems this might
get rid of your subnormal problems. Especially since performance seems to
be an issue it seems like the right thing to do. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
by: Roger Leigh |
last post by:
Hello,
I'm writing a fixed-precision floating point class, based on the ideas
in the example fixed_pt class in the "Practical C++ Programming" book
by Steve Oualline (O' Reilly). This uses a long int to store the
value, and the precision (number of decimal points) is variable (it's
a templated class):
template <size_t _decimal_places = 4>
class FixedFloat {
|
by: Dave |
last post by:
Hi folks,
I am trying to develop a routine that will handle sphere-sphere and
sphere-triangle collisions and interactions. My aim is to develop a
quake style collision engine where a player can interact with a rich
3D environment. Seem to be 90% of the way there! My problems are
related to calculations where the result tends to zero (or another
defined limit.)
Have loads of cases where this kind of interaction occurs but this one
|
by: JS |
last post by:
We have the same floating point intensive C++ program that runs on
Windows on Intel chip and on Sun Solaris on SPARC chips. The program
reads the exactly the same input files on the two platforms. However,
they generate slightly different results for floating point numbers.
Are they really supposed to generate exactly the same results? I
guess so because both platforms are supposed to be IEEE floating point
standard (754?) compliant. ...
|
by: cody |
last post by:
no this is no trollposting and please don't get it wrong but iam very
curious why people still use C instead of other languages especially C++.
i heard people say C++ is slower than C but i can't believe that. in pieces
of the application where speed really matters you can still use "normal"
functions or even static methods which is basically the same.
in C there arent the simplest things present like constants, each struct and
enum...
|
by: Shawn |
last post by:
Hello all,
I apologize as I am sure this has probably been dealth with before...
but I am doing an exercise from "Practical C Programming" and I have
been unable to get it to work perfectly due to problems with floating
point arithmetic and I am looking for a way to solve it. See the code
below...
Given a certain amount of change (below $1.00) the program will tell
you how many of each coin you will need to get that amount. The
program...
| | |
by: Vinoth |
last post by:
I'm working in an ARM (ARM9) system which does not have Floating point
co-processor or Floating point libraries. But it does support long long int
(64 bits).
Can you provide some link that would discuss about ways to emulate floating
point calculations with just long int or long long int. For eg., if i've a
formula X=(1-b)*Y + b*Z in floating point domain, i can calculate X with
just long ints (but, some data may be lost in final division;...
|
by: michael.mcgarry |
last post by:
Hi,
I have a question about floating point precision in C.
What is the minimum distinguishable difference between 2 floating point
numbers? Does this differ for various computers?
Is this the EPSILON? I know in float.h a FLT_EPSILON is defined to be
10^-5. Does this mean that the computer cannot distinguish between 2
numbers that differ by less than this epsilon?
|
by: ma740988 |
last post by:
template <class T> inline bool isEqual( const T& a, const T& b,
const T epsilon = std::numeric_limits<T>::epsilon() )
{
const T diff = a - b;
return ( diff <= epsilon ) && ( diff >= -epsilon );
}
int main()
{
std::deque<double> pt ;
|
by: ultimatewarrior |
last post by:
Hi all,
first of all I beg your pardon if this question has been asked
before, but I was unable to find anything in the past posts.
I have written a piece of code that was supposed to be quite portable,
and uses a lot fp numbers. Everything goes well on PPC cpus, but on
some x86 CPU I get a dramatic loss of performance. After some
investigations I've discovered that the problem is caused by some
numbers becoming subnormal, PPC cpus...
|
by: Hystou |
last post by:
Most computers default to English, but sometimes we require a different language, especially when relocating. Forgot to request a specific language before your computer shipped? No problem! You can effortlessly switch the default language on Windows 10 without reinstalling. I'll walk you through it.
First, let's disable language synchronization. With a Microsoft account, language settings sync across devices. To prevent any complications,...
|
by: Oralloy |
last post by:
Hello folks,
I am unable to find appropriate documentation on the type promotion of bit-fields when using the generalised comparison operator "<=>".
The problem is that using the GNU compilers, it seems that the internal comparison operator "<=>" tries to promote arguments from unsigned to signed.
This is as boiled down as I can make it.
Here is my compilation command:
g++-12 -std=c++20 -Wnarrowing bit_field.cpp
Here is the code in...
| | |
by: jinu1996 |
last post by:
In today's digital age, having a compelling online presence is paramount for businesses aiming to thrive in a competitive landscape. At the heart of this digital strategy lies an intricately woven tapestry of website design and digital marketing. It's not merely about having a website; it's about crafting an immersive digital experience that captivates audiences and drives business growth.
The Art of Business Website Design
Your website is...
|
by: Hystou |
last post by:
Overview:
Windows 11 and 10 have less user interface control over operating system update behaviour than previous versions of Windows. In Windows 11 and 10, there is no way to turn off the Windows Update option using the Control Panel or Settings app; it automatically checks for updates and installs any it finds, whether you like it or not. For most users, this new feature is actually very convenient. If you want to control the update process,...
|
by: agi2029 |
last post by:
Let's talk about the concept of autonomous AI software engineers and no-code agents. These AIs are designed to manage the entire lifecycle of a software development project—planning, coding, testing, and deployment—without human intervention. Imagine an AI that can take a project description, break it down, write the code, debug it, and then launch it, all on its own....
Now, this would greatly impact the work of software developers. The idea...
|
by: conductexam |
last post by:
I have .net C# application in which I am extracting data from word file and save it in database particularly. To store word all data as it is I am converting the whole word file firstly in HTML and then checking html paragraph one by one.
At the time of converting from word file to html my equations which are in the word document file was convert into image.
Globals.ThisAddIn.Application.ActiveDocument.Select();...
|
by: 6302768590 |
last post by:
Hai team
i want code for transfer the data from one system to another through IP address by using C# our system has to for every 5mins then we have to update the data what the data is updated we have to send another system
|
by: muto222 |
last post by:
How can i add a mobile payment intergratation into php mysql website.
| | |
by: bsmnconsultancy |
last post by:
In today's digital era, a well-designed website is crucial for businesses looking to succeed. Whether you're a small business owner or a large corporation in Toronto, having a strong online presence can significantly impact your brand's success. BSMN Consultancy, a leader in Website Development in Toronto offers valuable insights into creating effective websites that not only look great but also perform exceptionally well. In this comprehensive...
| |
