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Subject: Re: [boost] [Review] Boost.Endian
From: Phil Endecott (spam_from_boost_dev_at_[hidden])
Date: 2011-09-08 12:44:36

Beman Dawes wrote:
>> I'm not sure how widespread differing endianness between ints and
>> floats is across the various platforms.
> The Wikipedia article says it's uncommon, IIRC, but we need some real
> data on that.

I think it's vanishingly rare and can be ignored (as can any
non-ieee754 formats). The only case I'm aware of is the format of
doubles on the original (20-year-old) ARM FPA chip. This would store
the bytes of a double as 45670123, i.e the bytes are little-endian
within the words (like ints) but the two words are ordered big endian.

<anecdote>This chip was designed by 3 guys, and I shared an office with
2 of them at the time. One came from Acorn who had been using
little-endian ARM chips for years, and the other came from Apple (who
were about to put an ARM chip in the first Newton) and had a 68000
big-endian background. So perhaps it's not surprising that it got
muddled. (The third guy designed the divide-and-square-root unit,
nocturnally.) I doubt that more than a few hundred of these chips were
ever made, but the format was a bit more widespread because the chip
could be emulated by the OS through illegal instruction traps.</anecdote>

Cheers, Phil.

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