IEEE 754 revision

IEEE 754-2008 (previously known as IEEE 754r) was published in August 2008 and is a significant revision to, and replaces, the IEEE 754-1985 floating point standard. The revision extended the previous standard where it was necessary, added decimal arithmetic and formats, tightened up certain areas of the original standard which were left undefined, and merged in IEEE 854 (the radix-independent floating-point standard).

In a few cases, where stricter definitions of binary floating-point arithmetic might be performance-incompatible with some existing implementation, they were made optional.

The standard had been under revision since 2000, with a target completion date of December 2006. The revision of an IEEE standard broadly follows three phases:

On 11 June 2008, it was approved unanimously by the IEEE Revision Committee (RevCom), and it was formally approved by the IEEE-SA Standards Board on 12 June 2008. It was published on 29 August 2008.

Participation in drafting the standard was open to people with a solid knowledge of floating-point arithmetic. More than 90 people attended at least one of the monthly meetings, which were held in Silicon Valley, and many more participated through the mailing list.

Progress at times was slow, leading the chairman to declare at the September 15, 2005 meeting that "no progress is being made, I am suspending these meetings until further notice on those grounds". In December 2005, the committee reorganized under new rules with a target completion date of December 2006.

New policies and procedures were adopted in February 2006. In September 2006 a working draft was approved to be sent to the parent sponsoring committee (the IEEE Microprocessor Standards Committee, or MSC) for editing and to be sent to sponsor ballot.

The MSC accepted the draft on 9 October 2006; the draft sent to the MSC can be found here. Note that the draft has been changed significantly in detail during the balloting process.

The first sponsor ballot took place from 2006-11-29 through 2006-12-28. Of the 84 members of the voting body, 85.7% responded—78.6% voted approval. There were negative votes (and over 400 comments) so there was a recirculation ballot in March 2007; this received an 84% approval. There were sufficient comments (over 130) from that ballot that a third draft was prepared for second, 15-day, recirculation ballot which started in mid-April 2007. For a technical reason, the ballot process was restarted with the 4th ballot in October 2007; there were also substantial changes in the draft resulting from 650 voters' comments and from requests from the sponsor (the IEEE MSC); this ballot just failed to reach the required 75% approval. The 5th ballot had a 98.0% response rate with 91.0% approval, with comments leading to relatively small changes. The 6th, 7th, and 8th ballots sustained approval ratings of over 90% with progressively fewer comments on each draft; the 8th (which had no in-scope comments: 9 were repeats of previous comments and one referred to material not in the draft) was submitted to the IEEE Standards Revision Committee ('RevCom') for approval as an IEEE standard.

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