Formal comment #187 (defect)

Bytevectors: `big' and `little' endianness under-specified
Reported by: 	Ludovic Courtès
Version:	5.92

Email: ludovic.courtes at laas.fr

Section 2.1 of the report (page 5) requires implementations to support
the big' and little' endianness types but does not specify them.

This is an issue since beside byte ordering, "word" ordering may also
differ among encodings (either at the hardware level or among
software-implemented encodings). For instance, the GNU C Library
<ieee754.h> header shows that 3 different encodings of IEEE-754
doubles are in use at the hardware level, depending on both byte order
_and_ word order [0]. Likewise, GMP's integer export functions allow
for the full spectrum of integer encoding, thanks to the ORDER, ENDIAN
and SIZE arguments [1].

Therefore, I believe the meaning of big' and little' should be made
explicit, both for integer and IEEE double encoding. They should
probably reflect the encodings most commonly referred to under these
names. Thus, for integers, 8-bit atomic elements [2] should be
assumed. For IEEE doubles, little' and big' should correspond to cases
where both byte and word ordering are the same.

Thanks, Ludovic.

[0] ieee754.h

[1] http://www.swox.com/gmp/manual/Integer-Import-and-Export.html

[2] Using the terminology found in:

        http://en.wikipedia.org/wiki/Endian#Examples


RESPONSE:

A section defining these terms will be added in the next draft of the
report.