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This is an old revision of this page, as edited by 82.139.196.68 (talk) at 12:56, 19 February 2012 (→‎Examples: new section). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Article might benefit from outside views of the new standard

The present article is carefully-written and informative, but it appears to be the view 'as seen by members of the committee.' (It reads like an insider view, though there is nothing improper about that). Has the trade press commented on these activities? Are any companies planning to implement new chips based on it? Has there been any published criticism of the new standard? This kind of thing would be useful to add, if properly sourced. EdJohnston (talk) 16:38, 11 September 2008 (UTC)[reply]

Absolutely -- I think the 754r article has been a 'holding pattern' for the new standard revision as it evolved. So that becomes a historical record of that revision. Soon (as soon as the new standard is actually available -- it was published on 29.08.2008) it will be time to put together a new 'IEEE 754' article that reflects the new standard. mfc (talk) 19:43, 12 September 2008 (UTC)[reply]
An additional comment on the above -- the revision process was open: anyone could join the mailing list or attend the meetings (no membership of fees required), so there could not really be such a thing as an 'insider view'. More than 90 people participated in one or more meetings (some had 40+ attendeees), and over 100 voted in the ballots. And yes, there are three separate hardware implementations, to date. mfc (talk) 16:55, 28 September 2008 (UTC)[reply]
Now the standard is finally available from the IEEE, it's probably time to start a new description of the standard for Wikipedia -- perhaps a working document first? mfc (talk) 16:55, 28 September 2008 (UTC)[reply]
By an 'insider view', I only mean 'the view by the people who were creating the standard.' If a standard has impact in the real world, there should be people who were not part of the committee who have things to say about it. I know that the original IEEE FP standard had a lot of impact, since it greatly reduced the number of incompatible floating-point implementations that engineers had to program for.
I agree. The current IEEE 754-2008 looks like just a rename/copy of the old IEEE 754r article, which was only about the revision process and a summary of changes. That is probably worth having (as a separate article?), but it's really not what should be in IEEE 754-2008 mfc (talk) 08:57, 29 September 2008 (UTC)[reply]
User:mfc noted that there are three separate hardware implementations. Shouldn't that be mentioned in the article? Are these implementations documented anywhere? EdJohnston (talk) 17:49, 28 September 2008 (UTC)[reply]
Also agree, and again not really much to do with the 'revision' article. For the record, the three hardware implementations are in POWER6 (full decimal floating-point unit), IBM System z9 (assists+millicode), and IBM System z10 (full decimal floating-point unit). For more details follow links from [1]. mfc (talk) 08:57, 29 September 2008 (UTC)[reply]

Still not an 'outsider view', but to kick off a new write-up of the standard I have put together a replacement text. This is mostly new text, but with some from the old IEEE 754-1985 article. The existing text here I will move to IEEE 754 revision before replacing with the new text. All comments and (correct) edits welcome! There is plenty that can be improved. mfc (talk) 16:11, 3 October 2008 (UTC)[reply]

IEEE 854 redirects to here, but no mention of it is made within the article. Should a note be added to indicate that it has now merged with this standard? --Wm243 (talk) 13:52, 25 March 2009 (UTC)[reply]

Good point – have so added. mfc (talk) 16:13, 27 March 2009 (UTC)[reply]

The IEEE 754 revision article mentions a half precision format, but no mention is made of it here. Was this dropped from the specification? --Wm243 (talk) 12:43, 17 April 2009 (UTC)[reply]

It ended up being just one of the many interchange formats for binary, and is not a basic format. It is mentioned under 'Interchange formats'. mfc (talk) 14:59, 17 April 2009 (UTC)[reply]

Exception handling

"Exception handling", What about "Denormal" exception? —Preceding unsigned comment added by 149.156.67.102 (talk) 15:06, 15 December 2008 (UTC)[reply]

There is no 'denormal exception' in IEEE 754. The five possible exceptions are:
Invalid operation
Division by zero
Overflow
Underflow
Inexact
Underflow occurs when a non-zero result is both subnormal and inexact. mfc (talk) 16:55, 15 December 2008 (UTC)[reply]

Still about "Exception handling", a note concerning the "Division by zero". The 1985 definition was: "If the divisor is zero and the dividend is a finite nonzero number, then the division by zero exception shall be signaled." As new operations were added in the IEEE 754 revision, it has been chosen to change this definition to include other operations with similar behavior (e.g. log(0)). The new definition is: "The divideByZero exception shall be signaled if and only if an exact infinite result is defined for an operation on finite operands." Vincent Lefèvre (talk) 20:28, 12 February 2012 (UTC)[reply]

Why is it worth sticking that in? It doesn't describe the conditions for all the other exceptions never mind in such detail. There's tons more worthwhile stuff like the IEEE 754 1985 article has, it might be worth moving much of the common stuff there about operations to a common article. Dmcq (talk) 21:02, 12 February 2012 (UTC)[reply]
The page was giving explanations for the invalid, overflow and underflow exceptions. For consistency, it should also give an explanation for division by zero, in particular because the name of this exception can be misleading. Saying that the exceptions were the same as in the old standard was also misleading. I agree that there should be a common article. The changes could be mentioned on IEEE_754_revision. Vincent Lefèvre (talk) 23:36, 12 February 2012 (UTC)[reply]

Question

Why are half precision, binary16 and 16-bit floating point numbers mentioned a few times in the article, but are they not shown in the table under "Basic formats"? Same question for decimal32. If there's a good reason for that, it might be useful to explain it in the article. 81.83.41.159 (talk) 08:26, 2 August 2009 (UTC)[reply]

Because theys are not classified as "basic formats". You find them under "interchange formats". Basic formats have arithmetic operations specified for them, non-basic formats do not have that. That is, the standard recommends converting binary16 and decimal32 to a more presice format for doing arithmetic computations. That is in order to get smaller rounding errors. keka (talk) 10:18, 2 August 2009 (UTC)[reply]

In the current version, the table now includes the "interchange formats" binary16 and decimal32. However, the table is still in the "basic formats" section, so it's a little confusing as a reference -- why does the text say there are five formats when the table attached to it lists seven. You can figure it out by staring at it long enough, so I guess it's not wrong per se, but it might be cleaner to move that table from the "Basic Formats" sub-section higher up to the parent "Formats" section, or to a new sub-section. Bleachpuppy (talk) 22:35, 7 September 2010 (UTC)[reply]

VB.Net Conversion Code: IEEE754 to Hex to IEEE754

IEEE 754 to Hexadecimal Conversion... 

   Private Function ConvertHexToIEEE754(ByVal hexValue As String) As Single
       
       Try
           Dim iInputIndex As Integer = 0
           Dim iOutputIndex As Integer = 0
           Dim bArray(3) As Byte
           For iInputIndex = 0 To hexValue.Length - 1 Step 2
               bArray(iOutputIndex) = Byte.Parse(hexValue.Chars(iInputIndex) & hexValue.Chars(iInputIndex + 1), Globalization.NumberStyles.HexNumber)
               iOutputIndex += 1
           Next
           Array.Reverse(bArray)
           Return BitConverter.ToSingle(bArray, 0)
       Catch ex As Exception
           Throw New FormatException("The supplied hex value is either empty or in an incorrect format. Use the following format: 00000000", ex)
       End Try
   End Function

Hexadecimal to IEEE 754 Conversion... 

   Private Function ConvertIEEE754ToHex(ByVal SngValue As Single) As String
       
       Dim tmpBytes() As Byte
       Dim tmpHex As String = ""
       tmpBytes = BitConverter.GetBytes(SngValue)
       For b As Integer = tmpBytes.GetUpperBound(0) To 0 Step -1
           If Hex(tmpBytes(b)).Length = 1 Then tmpHex += "0" '0..F -> 00..0F
           tmpHex += Hex(tmpBytes(b))
       Next
       Return tmpHex
   End Function  —Preceding unsigned comment added by 59.160.73.114 (talk) 06:48, 11 November 2009 (UTC)[reply]

For more information please visit URL: http://weblogs.asp.net/craigg/archive/2006/09/25/Hexadecimal-to-Floating-Point-_2800_IEEE-754_2900_.aspx

This does not strike me as approprioate material for the article and this page is for discussions for improving the aticle. Dmcq (talk) 13:35, 11 November 2009 (UTC)[reply]

In a recent edit, an editor took out the link to a draft of the FP standard hosted at validlab.com, which is dated 2007. Since viewing of the current standard at the IEEE site is only available to subscribers, I suggest that the link to the ungated draft be restored to the article. EdJohnston (talk) 14:17, 26 July 2010 (UTC)[reply]

The draft has a copyright notice on its face. "Permission is hereby granted for IEEE Standards Committee participants to reproduce this document for purposes of international standardization consideration." Not clear that public dissemination fits that description. Glrx (talk) 16:21, 26 July 2010 (UTC)[reply]
Yes I agree, from the statements they put on the document it unfortunately looks like even putting a link to a copy would conflict with WP:COPYLINK. Dmcq (talk) 18:45, 26 July 2010 (UTC)[reply]
In the edit mentioned above, the motivation for removing the link to the obsolete version was out of concern that people might use or rely on outdated information in the draft version that may have changed in the final version. I didn’t know that access to the standards was restricted (the links worked when I tried them; I hadn’t considered my institution has a campus-wide subscription to IEEE Xplore). Although the link was admittedly not removed for copyright reasons, I think Dmcq read the policy right: “Knowingly and intentionally directing others to a site that violates copyright has been considered a form of contributory infringement in the United States (Intellectual Reserve v. Utah Lighthouse Ministry).” That said, those whose institutions don’t subscribe to IEEE Xplore (such as students in developing countries) can always Google for an illegitimate copy of the standard on the net; it’s not Wikipedia’s obligation to provide that service. Btw, for those in the U. S., buying the standard isn’t really that crazy an idea. I once sent away for a paper copy of the 754-1985 standard for an undergrad processor design project; it was the best $56 I ever spent. —Technion (talk) 10:15, 27 July 2010 (UTC)[reply]

The link to draft standard has been reintroduced, and I have been reverting it for the same reasons given above. There is no indication that IEEE has given permission for unlimited public release of the draft. I don't like that the standard isn't freely available, and I don't like removing the link to the draft. Unfortunately, I don't think the link is permitted. Please don't reintroduce the link without getting consensus on this page. Glrx (talk) 19:22, 13 December 2010 (UTC)[reply]

Many other draft standard documents are freely available, even when the final document is not free. Can someone figure out officially if this one should be available by link? (Maybe ask IEEE?) Gah4 (talk) 13:24, 24 September 2011 (UTC)[reply]

Misleading table?

The digits column of the table in the basic formats section might be a little misleading. I wasn't sure if it meant binary or decimal until I looked at the Wikipedia page on doubles. I think the column should be relabeled "binary digits". —Preceding unsigned comment added by 24.41.57.147 (talk) 04:58, 10 August 2010 (UTC)[reply]

I think a second column should also be added that lists approximate numbers of decimal digits of precision. —Preceding unsigned comment added by 24.41.57.147 (talk) 05:13, 10 August 2010 (UTC)[reply]

It wouldn't be then number of binary digits for the decimal formats. That's why the previous column gives the base. Didn't you wonder too about the +1 which is explained in the line just above the table? The standard doesn't give approximate decimal digits. The figures that could possibly be given are the various ones in IEEE 754-2008#Character representation. I'll stick a reference to that section under the table. Dmcq (talk) 09:14, 10 August 2010 (UTC)[reply]
I Just had a look at that section and it might not be best for the purpose. I think it would be allowable for me to stick the value of log10 2prescision in the table. This would give about 7.2 for binary32 whereas only 6 digits of a decimal number might be recovered going to it and back again and yet 9 digits are needed in decimal to ensure the binary value is got back again. Dmcq (talk) 10:17, 10 August 2010 (UTC)[reply]

Distinguishing zeroes

It might be worth mentioning that +0 and -0 can be distinguished, in a language that does not offer direct access to the bit pattern but allows infinity, by comparing their reciprocals. If X is a number that is not NaN, one can always determine the sign of X by testing (X + 1/X). JavaScript is such a language, and in it parseInt of a signed zero String returns a signed zero Number. 82.163.24.100 (talk) 22:27, 26 October 2010 (UTC)[reply]

And if X is a NaN? Don't encourage contorted programming practice / workarounds. If the sign needs to be determined, then use a function such as copysign. If the implementation doesn't have the facility, then it should be added to the implementation. Glrx (talk) 18:04, 27 October 2010 (UTC)[reply]

Citations etc.

Ran across this article mentioned in the Wikipedia:Articles for deletion/IEEE machine. Four articles on this subject is probably too many, but not user if we want one, two, or three. There is much material here, but very few inline citations, so seems mainly written from personal experience and thus hard to verify. IEEE floating point which might be the common name, redirects here, but it is the IEEE 754-1985 that has the diagrams and background that a general reader might be more interested in, so maybe we should redirect it back there, or else consider a merge. IEEE 754 revision seems mostly personal narrative, with only two inline links instead of citations. It looks like it was split off of this one in October 2008 or so. The articles are otherwise well-written, so not sure if a merge is worth it. It just now requires reading all three to make sense. From the first sentence in the lead, a reader would expect this to be an article on the standard in general, not one revision of it. There could be more in the future too. W Nowicki (talk) 18:15, 21 September 2011 (UTC)[reply]

I would also add that the only two inline citations are in the lead, and mention an alphabet soup that would be fairly meaningless to most readers. My guess is that the same format was approved by another standards body, but if so, that should be stated explicitly in the body, with a summary in the lead only. ISO/IEC/IEEE 60559:2011 ... JTC1/SC 25 ... ISO/IEEE PSDO is not English. Maybe somone should propose a Wikipedia written entirely in acronyms and stanards numbers. :-) W Nowicki (talk) 18:23, 21 September 2011 (UTC)[reply]

My personal choice would be a single article titled with the common name, IEEE floating point, with a redirect for the standards number as being more accessible to most readers, but that could be just me. (Do we have a guideline that expresses a preference either way for common names versus standards numbers?) I also struggled some with the IEEE 754 revision article, wondering just what additional value it offered. Msnicki (talk) 18:27, 21 September 2011 (UTC)[reply]
In some sense only one citation is needed -- to the actual Standard; all assertions in the Wikipedia article can be checked against that.
On the articles IEEE 754-2008, IEEE 754 revision, and IEEE 754-1985 -- it might make sense to merge the first and third, but a lot of new material would need to be added to get the 2008 additions covered as well as the 'old' basics from 1985. This would make it very big and long -- perhaps a different structure altogether is needed: the (currrent) '2008' article as top-level, pointing to "IEEE 754 binary formats" and "IEEE 754 decimal formats" which detail the bits and bytes.
I think the revision article is definitely best kept separate as it refers to the history and process rather than the content. Important stuff, because it shows that due diligence was done over the 7 years by dozens of people, but it is probably not what most readers will be looking for. mfc (talk) 13:08, 22 September 2011 (UTC)[reply]
I agree that just merging the 2008 and 1985 articles would make a mess of things. The 2008 standard has a lot of additions and changes in it and the 1985 one is what most machines currently implement. You'd get an article with lots of ifs in it where a lot wasn't applicable to what's mainly out there. This article already refers to separate articles for more down to earth aspects like binary or decimal formats but it could do with a lot more linking to describe other things. Dmcq (talk) 13:54, 22 September 2011 (UTC)[reply]

Well if the 1985 standard is what is most common, then perhaps IEEE floating point should at least point there and not here? Given the much sadder state of some other standards articles, it probably makes sense to just work on some of the sourcing for now and avoid the major work of merges, until when and if there is a clear way to improve things. I never formally proposed a merge because it was not clear which way to go. What I am trying to avoid is a deletion fight when someone comes along and cites the rule that any unsourced material may be removed at any time. I do find the narrative of the group history interesting to keep, as long as it does not overlap this article too much. Maybe just rewrite the lead of this one a bit to clarify what we are saying here. Wikipedia articles should talk about the standard (e.g. cite estimates for how widely they are used) but need not be complete enough to allow someone to implement from the article - that is that the standards documents themselves are for, or other books and articles on the subject. W Nowicki (talk) 18:00, 24 September 2011 (UTC)[reply]

Typography

The spurious space from the change http://en.wikipedia.org/w/index.php?title=IEEE_754-2008&oldid=453746074 looks rather strange. This change should probably be reverted. If a user has a problem with his browser (the problem described by the user doesn't occur in Firefox), the browser should be fixed, not Wikipedia. Vincent Lefèvre (talk) 01:28, 4 October 2011 (UTC)[reply]

256 bit AVX

Is it true that AVX supports 256 bit floats? And if it does i guess they would be in the style of ieee 754, or are they about to become part of the standard? --178.2.195.152 (talk) 18:08, 4 December 2011 (UTC)[reply]

No, what it support is doing a number of floating point operations in parallel, the V stands for vector which in effect means a number at a time. Dmcq (talk) 18:21, 4 December 2011 (UTC)[reply]
I think the IBM z10 series implements various 128 bit floating point formats in hardware and some older IBM and VAX systems also supported 128 bit foat though I believe they used a bit of software or microcode support via doubles. Dmcq (talk) 18:33, 4 December 2011 (UTC)[reply]
Quoting the FMA instruction set Article:
The FMA instruction set is the name of a future extension to the 128-bit SIMD instructions in the X86 microprocessor instruction set to perform fused multiply–add (FMA) operations
Both contain fused multiply–add (FMA) instructions for floating point scalar and SIMD operations.

Sounds to me as there where 128 bit registers that could be just either for SIMD operations or for FMA for floats that would be 128 bit long. Or am i missunderstanding things? --178.6.206.24 (talk) 18:33, 5 December 2011 (UTC)[reply]

And Bulldozer_(microarchitecture) :
Two symmetrical 128-bit FMAC (fused multiply–add capability) floating-point pipelines per module that can be unified into one large 256-bit-wide unit if one of integer cores dispatch AVX instruction and two symmetrical x87/MMX/SSE capable FPPs for backward compatibility with SSE2 non-optimized software

Or does it simply mean that four 64 bit floats are processed at the same time? --178.6.206.24 (talk) 18:38, 5 December 2011 (UTC)[reply]

The operations deal with a number of floating point operations at a time, for instance one can do eight single precision or four double precision operations at a time with the 256 bit registers. The bit about the two 128 bits being used as a 256 bit is that for two cores on a chip their floating point power can be shared rather than spending a pile of silicon on separate parallel floating point units for the 256 bit vectors. Dmcq (talk) 20:57, 5 December 2011 (UTC)[reply]

Details please

Question: In IEEE 754, which bits/bytes are used as the significand and the exponent? What code is used for infinity, and NaN? This detail should be included in the article, in case anyone's curious. 68.173.113.106 (talk) 21:06, 28 January 2012 (UTC)[reply]
Click on the blue link for the particular format you're interested in to get details about it. Dmcq (talk) 23:09, 28 January 2012 (UTC)[reply]

Examples

This article needs examples!

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