Re: [boost] [Review] Boost.Endian

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.