mersenneforum.org  

Go Back   mersenneforum.org > Great Internet Mersenne Prime Search > Hardware

Reply
 
Thread Tools
Old 2011-02-03, 00:14   #1
ixfd64
Bemusing Prompter
 
ixfd64's Avatar
 
"Danny"
Dec 2002
California

1001011110002 Posts
Default translating double to single precision?

I know that it's generally very hard to efficiently convert single to double precision, except in the case of nVidia's high-end Fermi GPUs. But what about the other way around? For example, would 100 GFLOPS of double precision easily convert to 200 GFLOPS of single precision?

Sorry if this is a dumb question.
ixfd64 is offline   Reply With Quote
Old 2011-02-03, 00:28   #2
rogue
 
rogue's Avatar
 
"Mark"
Apr 2003
Between here and the

29×223 Posts
Default

Simply put, no. In other words, An FPU cannot do twice as much SP work in the same amount of time as DP work just because the size of the variables it is working with are half the size. One of the reasons is that the FP registers are 64 bits and can only hold one value. You can't put two 32-bit values in a 64-bit FP register. WRT vector programming, that doesn't apply.

Last fiddled with by rogue on 2011-02-03 at 00:29
rogue is offline   Reply With Quote
Old 2011-02-04, 06:26   #3
ixfd64
Bemusing Prompter
 
ixfd64's Avatar
 
"Danny"
Dec 2002
California

23·3·101 Posts
Default

Yeah, I was thinking of vector processing. I do know that Intel's "Sandy Bridge" chips are supposed to be up to twice as fast as those of the previous generation due to the use of 256-bit registers. Strangely, the FLOPS numbers of the newly released chips do not reflect this, but then again, FLOPS are not the only means of measuring a processor's performance.
ixfd64 is offline   Reply With Quote
Old 2012-09-11, 23:55   #4
ixfd64
Bemusing Prompter
 
ixfd64's Avatar
 
"Danny"
Dec 2002
California

1001011110002 Posts
Default

Sorry for bumping such an old thread, but some of the slides from IDF 2012 show that Intel's newer chips are able to do twice as many SP FLOPS as DP FLOPS per clock cycle. Interesting.

Last fiddled with by ixfd64 on 2012-09-11 at 23:56 Reason: missing "to"
ixfd64 is offline   Reply With Quote
Old 2012-09-12, 01:13   #5
ewmayer
2ω=0
 
ewmayer's Avatar
 
Sep 2002
Rep├║blica de California

101101100111002 Posts
Default

Quote:
Originally Posted by ixfd64 View Post
Sorry for bumping such an old thread, but some of the slides from IDF 2012 show that Intel's newer chips are able to do twice as many SP FLOPS as DP FLOPS per clock cycle. Interesting.
That still makes DP a clear win for bignum-style FFTs, since DP permits more than 2x the number of bits per input word as SP. (In other words a DP FFT can use vectors less than half the length.
ewmayer is offline   Reply With Quote
Old 2012-09-12, 05:10   #6
LaurV
Romulan Interpreter
 
LaurV's Avatar
 
"name field"
Jun 2011
Thailand

24×613 Posts
Default

That for sure. Win for SP would be for (about) 9 to 12 SPFlops per DPFlop. Think about a very simple example: multiplying two DPFloat numbers A*f+B and C*f+D, where f is the size of a SPFloat, you need 4 SPFloats to store them and you need 4 SPFlops to multiply them (or 3 with Karatsuba, with some overload of additions and subtractions). If you can multiply the two DPFloats in a single flop, then you are 4 times faster already. Add this to the ability to store larger numbers (when you do carry propagation) and/or more accurate/higher precision and you see that 2 times (even 4 times) faster SPFlops is not enough to beat DP.

Another example, think to very fast video cards, which can get almost 2 TeraFlops of SP, but only 300-400 GigaFlops of DP (5-6 times less). If "times 4" or "times 5" would be enough, why the manufacturers don't use (micro)programming to do a DPFlop with 4 SPflops?
LaurV is offline   Reply With Quote
Reply

Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
does half-precision have any use for GIMPS? ixfd64 GPU Computing 9 2017-08-05 22:12
Fast double precision Division __HRB__ Programming 21 2012-01-10 02:10
so what GIMPS work can single precision do? ixfd64 Hardware 21 2007-10-16 03:32
Double precision GPUs coming very soon dsouza123 Hardware 4 2007-10-15 02:20
double precision in LL tests drew Software 4 2006-08-08 04:08

All times are UTC. The time now is 15:41.


Fri Dec 3 15:41:11 UTC 2021 up 133 days, 10:10, 0 users, load averages: 1.32, 1.23, 1.25

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.

This forum has received and complied with 0 (zero) government requests for information.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation.
A copy of the license is included in the FAQ.