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| Date | 2011-10-19 10:37 +0200 |
|---|---|
| From | Terje Mathisen <"terje.mathisen at tmsw.no"> |
| Newsgroups | comp.arch |
| Subject | Re: Infinity + Infinity (or NegInfinity - NegInfinity) |
| References | <89f27$4e8f9f40$5419acc3$12829@cache4.tilbu1.nb.home.nl> <9s70n8-krv2.ln1@ntp6.tmsw.no> <j7jrkp$iib$1@gosset.csi.cam.ac.uk> <6lj0n8-2903.ln1@ntp6.tmsw.no> <j7kapu$lb9$1@gosset.csi.cam.ac.uk> |
| Message-ID | <ase2n8-151.ln1@ntp6.tmsw.no> (permalink) |
nmm1@cam.ac.uk wrote:
> In article<6lj0n8-2903.ln1@ntp6.tmsw.no>,
> Terje Mathisen<"terje.mathisen at tmsw.no"> wrote:
>>
>>>> You could do this by taking the result, masking away all mantissa bits
>>>> and saving it as temp1, then set the ulp bit and save as temp2.
>>>
>>> Er, you have to ADD one ULP, not just force the bit!
>>>
>>>> Finally you use your random generator/stream to select either temp1 or
>>>> temp2 to be added and then subtract temp1 afterwards.
>>>>
>>>> Does that seem OK?
>>>
>>> With my corrections, yes.
>>
>> Please re-read:
>>
>> The forced ulp bit is randomly added or not.
>
> Aargh! You were assuming a hidden bit and I was assume that there
> wasn't one! If you don't have one, there is no point in all that
> faffing around with temp1.
First of all: Both float and double does have hidden bits...
Second, I really don't get how you would like your code to work, here is
my version:
/* Rounding mode is set globally to -Inf */
double fmul(double a, double b)
{
double prod = a*b;
int64_t temp[2];
/* Keep sign and exponent, clear mantissa (except for hidden bit):
This is the same as the integer binary log
*/
temp[0] = (*(int64_t *) &prod) & 0xfff0000000000000;
/* Same as temp[0] but rounded up to the next ulp value */
temp[1] = temp[0] | 1;
/* Generate the randomly rounded product by adding either
temp[0] or the successor temp[1], then subtract temp[0]
*/
prod += ((double *) temp)[get_random_bit()];
prod -= ((double *) temp)[0];
return prod;
}
The timing is as follows:
Generate prod, store to local stack location: 5-6 cycles
Load as int64_t, mask and save: 3 cycles
Increment and save: 2 cycles
Load either first or second element as double: 1 cycle +
get_random_bit() overhead, but that can be overlapped with all the
previous calculations, so I'll assume it is free.
FADD + FSUB: 8 cycles
I.e the total is about 20 cycles, or 5 times more than a plain FMUL.
Terje
--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"
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Infinity + Infinity (or NegInfinity - NegInfinity) "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-10-08 02:54 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Robert Myers <rbmyersusa@gmail.com> - 2011-10-07 18:40 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) James Kuyper <jameskuyper@verizon.net> - 2011-10-07 22:39 -0400
Re: Infinity + Infinity (or NegInfinity - NegInfinity) William Elliot <marsh@rdrop.com> - 2011-10-07 19:56 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Jasen Betts <jasen@xnet.co.nz> - 2011-10-08 06:45 +0000
Re: Infinity + Infinity (or NegInfinity - NegInfinity) gordonb.eug6r@burditt.org (Gordon Burditt) - 2011-10-08 02:37 -0500
Re: Infinity + Infinity (or NegInfinity - NegInfinity) William Elliot <marsh@rdrop.com> - 2011-10-08 21:40 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Kaba <kaba@nowhere.com> - 2011-10-09 12:17 +0300
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Jasen Betts <jasen@xnet.co.nz> - 2011-10-08 06:33 +0000
Re: Infinity + Infinity (or NegInfinity - NegInfinity) "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-10-08 16:41 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) kenney@cix.compulink.co.uk - 2011-10-09 04:01 -0500
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Kaba <kaba@nowhere.com> - 2011-10-08 17:43 +0300
Re: Infinity + Infinity (or NegInfinity - NegInfinity) "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2011-10-08 10:20 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Kaba <kaba@nowhere.com> - 2011-10-08 22:35 +0300
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-08 18:55 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Kaba <kaba@nowhere.com> - 2011-10-08 23:03 +0300
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-08 21:27 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) James Kuyper <jameskuyper@verizon.net> - 2011-10-08 17:28 -0400
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Robert Myers <rbmyersusa@gmail.com> - 2011-10-08 18:15 -0400
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-08 23:23 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) James Kuyper <jameskuyper@verizon.net> - 2011-10-08 21:29 -0400
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-09 10:01 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Al Grant <algrant@myrealbox.com> - 2011-10-12 06:14 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-12 15:25 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) James Kuyper <jameskuyper@verizon.net> - 2011-10-12 12:10 -0400
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-12 18:41 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) James Kuyper <jameskuyper@verizon.net> - 2011-10-12 15:32 -0400
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-12 20:44 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Robert Myers <rbmyersusa@gmail.com> - 2011-10-12 18:11 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Andrew Reilly <areilly---@bigpond.net.au> - 2011-10-13 03:48 +0000
Re: Infinity + Infinity (or NegInfinity - NegInfinity) "Paul A. Clayton" <paaronclayton@gmail.com> - 2011-10-12 23:15 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-13 09:12 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) "Paul A. Clayton" <paaronclayton@gmail.com> - 2011-10-13 00:49 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-13 10:37 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) EricP <ThatWouldBeTelling@thevillage.com> - 2011-10-13 11:04 -0400
Re: Infinity + Infinity (or NegInfinity - NegInfinity) EricP <ThatWouldBeTelling@thevillage.com> - 2011-10-13 17:15 -0400
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-14 09:22 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) EricP <ThatWouldBeTelling@thevillage.com> - 2011-10-14 13:37 -0400
Re: Infinity + Infinity (or NegInfinity - NegInfinity) "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-10-13 11:11 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Al Grant <algrant@myrealbox.com> - 2011-10-14 01:04 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-13 09:07 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Al Grant <algrant@myrealbox.com> - 2011-10-13 07:00 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Robert Myers <rbmyersusa@gmail.com> - 2011-10-14 10:54 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Andrew Reilly <areilly---@bigpond.net.au> - 2011-10-14 22:36 +0000
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-15 09:26 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) "Paul A. Clayton" <paaronclayton@gmail.com> - 2011-10-15 05:39 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-15 14:56 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-17 08:37 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-17 12:03 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-17 11:13 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-17 22:30 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) "Paul A. Clayton" <paaronclayton@gmail.com> - 2011-10-17 14:47 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-18 11:33 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-18 10:21 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-18 08:16 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-18 14:26 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-18 13:32 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-18 17:47 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-18 17:51 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-19 10:37 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-19 09:36 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-19 11:46 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-19 10:45 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-19 13:11 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-19 12:12 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-19 16:22 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-19 15:16 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Andrew Reilly <areilly---@bigpond.net.au> - 2011-10-15 20:16 +0000
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Robert Myers <rbmyersusa@gmail.com> - 2011-10-15 16:26 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-17 08:14 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) nmm1@cam.ac.uk - 2011-10-17 08:22 +0100
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-17 11:39 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) rpw3@rpw3.org (Rob Warnock) - 2011-10-17 21:00 -0500
Re: Infinity + Infinity (or NegInfinity - NegInfinity) "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-10-18 05:44 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-10-17 21:35 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Jasen Betts <jasen@xnet.co.nz> - 2011-10-24 02:40 +0000
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-10-27 00:32 +0300
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-27 10:41 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-10-27 13:10 +0300
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-27 13:53 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Keith Thompson <kst-u@mib.org> - 2011-10-12 12:34 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Al Grant <algrant@myrealbox.com> - 2011-10-13 06:39 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) James Kuyper <jameskuyper@verizon.net> - 2011-10-13 10:34 -0400
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Al Grant <algrant@myrealbox.com> - 2011-10-14 00:54 -0700
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Larry Hewitt <larryhwtt@comporium.net> - 2011-10-09 21:35 -0400
Re: Infinity + Infinity (or NegInfinity - NegInfinity) "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-10-10 04:37 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Larry Hewitt <larryhwtt@comporium.net> - 2011-10-10 13:58 -0400
Re: Infinity + Infinity (or NegInfinity - NegInfinity) "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-10-13 20:17 +0200
Re: Infinity + Infinity (or NegInfinity - NegInfinity) Arivald <arivald_@AT_interia_DOT_.pl> - 2011-10-13 12:10 +0200
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