Decimal floating point on x86 and ARM?

By: Per Hesselgren (perhesselgren.delete@this.yahoo.se), December 21, 2020 4:33 am
Room: Moderated Discussions
blaine (myname.delete@this.acm.org) on December 20, 2020 11:40 am wrote:
> Konrad Schwarz (no.spam.delete@this.no.spam) on December 20, 2020 8:47 am wrote:
> > anon (an.delete@this.n.com) on December 18, 2020 8:29 am wrote:
> > > I read that C2X (the next C language revision) will add support for decimal floating point.
> > > I know that POWER and SPARC CPUs have hardware support for decimal FP,
> > > but are there any plans to include it on future x86 or ARM CPUs?
> >
> > The x87 supports a decimal floating point format, but I don't
> > know if it is compatible to IEEE decimal floating
> > point; the x87 format is a sign bit followed by 18 BCD digits and no exponent, so I expect not.
> >
> > As an aside, I recently read "The 8087 Primer" by John F. Palmer & Stephen P. Morse from
> > 1983 and it is really a good introduction to floating point and the x87 -- I believe Palmer
> > was the architect of the 8087. E.g., this clearly states that the round to infinity and
> > round to minus infinity rounding modes were designed for interval arithmetic.
>
> Palmer was the architect of the Intel floating point unit. There was a meeting where new guys were
> asked if they had taken numerical analysis, that how I ended up writing the first floating point
> test suite for Intel (me and a Tech Kurt?). Never raise your hand. Palmer was one of the nicest
> people that I ever worked with and I learned so much on the project. Kahan consulted. The first
> hardware we had to test was the sbc-310. Palmer also wrote a floating point simulator in PLM.
>
> Morse was the architect of the 8086. He is brilliant. The x86 instruction architecture gets a lot of sand kicked
> on it, but given the constraints for compatibility and the technology of the day, he did a great job.
>
> Indeed round to positive and negative infinities were there to support interval arithmetic. Non
> biased rounding was introduced also. There was talk of imprecise compares for floating point (that
> got squashed when I pointed out that it could break the Transitive property for equality.)

In C/C++ long double is 10 bytes for X86_64 but 16 bytes for ARM64 and 8 bytes for ARM32
< Previous Post in ThreadNext Post in Thread >
TopicPosted ByDate
Decimal floating point on x86 and ARM?anon2020/12/18 09:29 AM
  Decimal floating point on x86 and ARM?Per Hesselgren2020/12/18 10:16 AM
    Decimal floating point on x86 and ARM?anon2020/12/18 12:23 PM
      Decimal floating point on x86 and ARM?dmcq2020/12/18 06:18 PM
  Decimal floating point on x86 and ARM?rwessel2020/12/18 07:57 PM
    Decimal floating point on x86 and ARM?dmcq2020/12/19 04:41 AM
      Decimal floating point on x86 and ARM?rwessel2020/12/19 08:54 AM
        Decimal floating point on x86 and ARM?Michael S2020/12/19 10:48 AM
          Decimal floating point on x86 and ARM?rwessel2020/12/20 09:25 AM
            Decimal floating point on x86 and ARM?blaine2020/12/20 11:52 AM
              Decimal floating point on x86 and ARM?rwessel2020/12/20 01:44 PM
                Decimal floating point on x86 and ARM?blaine2020/12/20 05:29 PM
              Decimal floating point on x86 and ARM?Konrad Schwarz2020/12/21 04:17 AM
            Decimal floating point on x86 and ARM?Adrian2020/12/21 10:05 AM
  Decimal floating point on x86 and ARM?Konrad Schwarz2020/12/20 09:47 AM
    Decimal floating point on x86 and ARM?rwessel2020/12/20 11:28 AM
    Decimal floating point on x86 and ARM?Linus Torvalds2020/12/20 11:39 AM
      Decimal floating point on x86 and ARM?dmcq2020/12/20 12:06 PM
        Decimal floating point on x86 and ARM?Konrad Schwarz2020/12/21 03:31 AM
          Decimal floating point on x86 and ARM?Brendan2020/12/21 05:49 AM
            Decimal floating point on x86 and ARM?dmcq2020/12/21 07:59 AM
      Decimal floating point on x86 and ARM?Adrian2020/12/21 09:51 AM
        Decimal floating point on x86 and ARM?Linus Torvalds2020/12/21 12:12 PM
          Decimal floating point on x86 and ARM?Adrian2020/12/21 01:29 PM
          Decimal floating point on x86 and ARM?dmcq2020/12/21 04:13 PM
      Decimal floating point on x86 and ARM?David Hess2020/12/21 07:15 PM
        Decimal floating point on x86 and ARM?Konrad Schwarz2020/12/22 01:04 AM
          Decimal floating point on x86 and ARM?David Hess2020/12/22 01:05 PM
    Decimal floating point on x86 and ARM?blaine2020/12/20 12:40 PM
      Decimal floating point on x86 and ARM?Per Hesselgren2020/12/21 04:33 AM
        Decimal floating point on x86 and ARM?rwessel2020/12/21 06:17 AM
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