What endiannesses do D support?
Some of druntime/phobos code assumes it is one of little/big endianness others have `static assert(0)` for third case. Lets clear the situation and make a decision. -- Денис В. Шеломовский Denis V. Shelomovskij
Re: What endiannesses do D support?
On Friday, 4 October 2013 at 10:59:05 UTC, Denis Shelomovskij wrote: Some of druntime/phobos code assumes it is one of little/big endianness others have `static assert(0)` for third case. Lets clear the situation and make a decision. Little endian and big endian must be supported. Little endian PowerPC, for example, is extremely rare (if not entirely extinct), so just supporting little endian is not enough.
Re: What endiannesses do D support?
04.10.2013 15:00, Alex Rønne Petersen пишет: On Friday, 4 October 2013 at 10:59:05 UTC, Denis Shelomovskij wrote: Some of druntime/phobos code assumes it is one of little/big endianness others have `static assert(0)` for third case. Lets clear the situation and make a decision. Little endian and big endian must be supported. Little endian PowerPC, for example, is extremely rare (if not entirely extinct), so just supporting little endian is not enough. Of course. The question is about a third case. -- Денис В. Шеломовский Denis V. Shelomovskij
Re: What endiannesses do D support?
On 04/10/2013 11:59, Denis Shelomovskij wrote: Some of druntime/phobos code assumes it is one of little/big endianness others have `static assert(0)` for third case. Lets clear the situation and make a decision. Are you thinking of middle-endian orders such as 2,3,0,1? Or just wondering in what situations neither BigEndian nor LittleEndian would be set? I suppose that most, if not all, 32+-bit machines are either big-endian or little-endian. But still, I imagine that the third-case is just a safeguard in case it is missed when somebody comes across a middle-endian platform and tries to compile that code on it. Or maybe it was just put in out of belief that it is a good programming practice. Endianness support as far as the D language is concerned doesn't seem to be clear-cut. http://dlang.org/version.html lists LittleEndian and BigEndian, but doesn't state that one of these will always be set. So middle-endian machines, if a D compiler exists for them, would use this third case. Further work would be needed to determine what particular middle-endian order the machine implements for each size of integer. (Floating points are even more complicated, so I guess you can't rely on any version flag to tell you about the format of these.) OTOH, the platforms on which DMD runs are big-endian or little-endian. If DMD is ported to a middle-endian platform, or the DMD Phobos/druntime code is cribbed for use with a third-party D compiler for a middle-endian machine, then the static assert will fire, thereby drawing attention to this unimplemented functionality rather than silently generating code that won't work because it's written for a little-endian machine, or for a big-endian machine. Stewart. -- My email address is valid but not my primary mailbox and not checked regularly. Please keep replies on the 'group where everybody may benefit.
Re: What endiannesses do D support?
On 10/4/13 3:26 PM, Stewart Gordon wrote:
On 04/10/2013 11:59, Denis Shelomovskij wrote:
Some of druntime/phobos code assumes it is one of little/big endianness others
have
`static assert(0)` for third case. Lets clear the situation and make a decision.
Are you thinking of middle-endian orders such as 2,3,0,1? Or just wondering in
what situations
neither BigEndian nor LittleEndian would be set?
I suppose that most, if not all, 32+-bit machines are either big-endian or
little-endian. But
still, I imagine that the third-case is just a safeguard in case it is missed
when somebody comes
across a middle-endian platform and tries to compile that code on it. Or maybe
it was just put in
out of belief that it is a good programming practice.
Endianness support as far as the D language is concerned doesn't seem to be
clear-cut.
http://dlang.org/version.html
lists LittleEndian and BigEndian, but doesn't state that one of these will
always be set. So
middle-endian machines, if a D compiler exists for them, would use this third
case. Further work
would be needed to determine what particular middle-endian order the machine
implements for each
size of integer. (Floating points are even more complicated, so I guess you
can't rely on any
version flag to tell you about the format of these.)
OTOH, the platforms on which DMD runs are big-endian or little-endian. If DMD
is ported to a
middle-endian platform, or the DMD Phobos/druntime code is cribbed for use with
a third-party D
compiler for a middle-endian machine, then the static assert will fire, thereby
drawing attention to
this unimplemented functionality rather than silently generating code that
won't work because it's
written for a little-endian machine, or for a big-endian machine.
Stewart.
Good answer. I'll add only one point: The use of the else static assert is a good way to catch a
new platform that's one of little or big but fails to specify. If the code instead did if (little)
{...} else {...}, the wrong choice would be potentially made. Better to require explicitness.
