in reply to Re^15: Math::BigFloat to native double?
in thread Math::BigFloat to native double?

I find the doubledouble to be rather intriguing (not to mention a little exasperating), and I purchased the (second hand) PPC box for the sole purpose of looking more readily at it.

I'm gonna ask this again: are you sure that we are talking about the same thing with respect to doubledouble and PPC?

When I google "PPC doubledouble" (and click past its annoying habit of trying to be helpful instead of searching for what I ask for), the *only* hits I get are those that also include (one of) your handles. Here, or on active state forums etc.

But, when I look at the C code there, I see "long double"; which according to wikipedia: MS map to double; Intel map to 80-bit IEEE (hardware) extended precision; and gcc maps to 128-bit IEEE quad precision. None of which are the doubledouble I'm talking of.

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
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  • Comment on Re^16: Math::BigFloat to native double?

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Re^17: Math::BigFloat to native double?
by syphilis (Archbishop) on Jul 16, 2015 at 12:28 UTC
    are you sure that we are talking about the same thing with respect to doubledouble and PPC

    Yes - though "being sure" doesn't guarantee that I'm right ;-)

    The wikipedia "long double" page mentions a number of ways of implementing long doubles, including the double double:

    "On some PowerPC and SPARCv9 machines, long double is implemented as a double-double arithmetic, where a long double value is regarded as the exact sum of two double-precision values, giving at least a 106-bit precision; with such a format, the long double type does not conform to the IEEE floating-point standard."

    Also this Wikipedia "double-double arithmetic" entry accurately describes the PPC double-double (and, I think, the double-double that you are wanting to implement).

    Cheers,
    Rob
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