From an article about implementing a C99 to C90 translator...
How does someone use integer arithmetic of at least 64 bits, and write in
pure C90?
As I understand C90 (the standard is very elusive), long int is guaranteed
to be at least 32 bits only.
So, do people rely on their known compiler limits, use clunky emulations, or
do not bother with 64 bits when writing ultra-portable code?
--
Bart
28  4918 
On Sun, 06 Apr 2008 15:37:28 +0000, Bartc wrote:
From an article about implementing a C99 to C90 translator...
How does someone use integer arithmetic of at least 64 bits, and write
in pure C90?
As I understand C90 (the standard is very elusive), long int is
guaranteed to be at least 32 bits only.
Correct. And as long int is the widest type, C90 does not guarantee the
presence of any 64-bit integer type.
So, do people rely on their known compiler limits, use clunky
emulations, or do not bother with 64 bits when writing ultra-portable
code?
People do whatever works best for their situation. Sometimes, that may
involve redefining the problem to fit 32-bit arithmetic (or floating-
point). Sometimes, that may be to rely on long being 64 bits. Sometimes,
that may be to use implementation extensions. In any case, it's very much
the same as how C90 programs have to deal with complex arithmetic. The
language and library don't provide any possibility, so portable programs
have no choice but to implement it themselves.
On Sun, 06 Apr 2008 15:37:28 GMT, "Bartc" <bc@freeuk.comw rote:
>From an article about implementing a C99 to C90 translator...
How does someone use integer arithmetic of at least 64 bits, and write in
pure C90?
As I understand C90 (the standard is very elusive), long int is guaranteed
to be at least 32 bits only.
So, do people rely on their known compiler limits, use clunky emulations, or
do not bother with 64 bits when writing ultra-portable code?
Many use a "big number library" that simulates arithmetic on very wide
integers. I think Richard Heathfield put one on the web and google
can probably find you others.
Remove del for email
Barry Schwarz wrote:
On Sun, 06 Apr 2008 15:37:28 GMT, "Bartc" <bc@freeuk.comw rote:
>>From an article about implementing a C99 to C90 translator...
How does someone use integer arithmetic of at least 64 bits, and write in
pure C90?
As I understand C90 (the standard is very elusive), long int is guaranteed
to be at least 32 bits only.
So, do people rely on their known compiler limits, use clunky emulations, or
do not bother with 64 bits when writing ultra-portable code?
Many use a "big number library" that simulates arithmetic on very wide
integers. I think Richard Heathfield put one on the web and google
can probably find you others.
Remove del for email
That GUARANTEES that the software will run VERY slowly using
ALL the CPU for nothing. Heathfield's big numbers use characters
as the base representation.
--
jacob navia
jacob at jacob point remcomp point fr
logiciels/informatique http://www.cs.virginia.edu/~lcc-win32
Barry Schwarz said:
<snip>
Many use a "big number library" that simulates arithmetic on very wide
integers.
Right.
I think Richard Heathfield put one on the web
Actually, no, I haven't. I've got one, but I haven't published it.
As Mr Navia notes elsethread, it uses an array of unsigned char to store
the data. He seems to think that this "GUARANTEES that the software will
run VERY slowly using ALL the CPU for nothing". It doesn't, of course.
Nevertheless, performance was not my highest priority. Those who want a
super-fast bignum library would be well advised to use GMP or Miracl.
--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999
jacob navia <ja***@nospam.c omwrites:
Bartc wrote:
>From an article about implementing a C99 to C90 translator...
Interesting interesting.
And when you are going to do a C89 to K&R translator?
It's been done; google "ansi2knr". Though as I recall it's not a
complete translator; mostly it converts prototypes to old-style
function declarations.
The point, of course, is that a C89 to K&R translator, though it was
quite useful years ago, is no longer of much interest today, since the
C89 standard is almost universally supported (it would be difficult to
find a platform that has a K&R compiler but no C89 compiler). This is
not yet the case for C99, a fact that you insist on ignoring, even
though your own lcc-win doesn't support the full language.
A C99 compiler that uses C89 as its intermediate language might be a
very useful thing. If it managed to generate portable C89 code, it
could even permit the use of C99 on platforms where no C99 compiler
yet exists (something I would think you'd welcome).
I suspect that modifying an existing C89 compiler to handle C99 would
be easier than writing a complete translator (but the latter would
potentially only have to be done once for all target platforms).
How does someone use integer arithmetic of at least 64 bits, and
write in pure C90?
There is no 64 bit arithmetic in C89. And you will have to do it
yourself!
Yes, that's probably one of the more difficult aspects of translating
C99 to C89. A quibble, though: C89 has no *guaranteed* 64-bit
arithmetic; it's perfectly legal to make long 64 bits.
--
Keith Thompson (The_Other_Keit h) <ks***@mib.or g>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
Richard Heathfield wrote:
Barry Schwarz said:
<snip>
>Many use a "big number library" that simulates arithmetic on very wide
integers.
Right.
>I think Richard Heathfield put one on the web
Actually, no, I haven't. I've got one, but I haven't published it.
As Mr Navia notes elsethread, it uses an array of unsigned char to store
the data. He seems to think that this "GUARANTEES that the software will
run VERY slowly using ALL the CPU for nothing". It doesn't, of course.
Nevertheless, performance was not my highest priority. Those who want a
super-fast bignum library would be well advised to use GMP or Miracl.
Using a char to store bignum data is like using a scooter to
move a 38 ton trailer.
It will work of course, and the 38 ton trailer will have a cruising
speed of several centimeters/hour...
Who cares?
That solution is PORTABLE. You can carry a scooter anywhere, they
are standard solutions, etc.
Portability means very often that you make mediocre software
that runs anywhere because it never uses the hardware/OS to
its maximum possibilities but just uses the least common
denominator of each one.
This is fine if you do not care about usability or similar problems.
GUIs?
Not portable. The command line is portable. Use the command line
Network?
Not portable...
Etc.
But this is more a philosophical question. Heathfield's viewpoint
is perfectly acceptable if you say:
Usability is less valuable than portability.
As he said, performance wasn't a concern for his software.
Portability was.
Result?
A mediocre but perfectly portable software.
--
jacob navia
jacob at jacob point remcomp point fr
logiciels/informatique http://www.cs.virginia.edu/~lcc-win32
jacob navia <ja***@nospam.c omwrites:
Richard Heathfield wrote:
>Barry Schwarz said:
<snip>
>>Many use a "big number library" that simulates arithmetic on very wide
integers.
Right.
>>I think Richard Heathfield put one on the web
Actually, no, I haven't. I've got one, but I haven't published it.
As Mr Navia notes elsethread, it uses an array of unsigned char to
store the data. He seems to think that this "GUARANTEES that the
software will run VERY slowly using ALL the CPU for nothing". It
doesn't, of course. Nevertheless, performance was not my highest
priority. Those who want a super-fast bignum library would be well
advised to use GMP or Miracl.
Using a char to store bignum data is like using a scooter to
move a 38 ton trailer.
It will work of course, and the 38 ton trailer will have a cruising
speed of several centimeters/hour...
Who cares?
That solution is PORTABLE. You can carry a scooter anywhere, they
are standard solutions, etc.
Portability means very often that you make mediocre software
that runs anywhere because it never uses the hardware/OS to
its maximum possibilities but just uses the least common
denominator of each one.
This is fine if you do not care about usability or similar problems.
GUIs?
Not portable. The command line is portable. Use the command line
Network?
Not portable...
Etc.
But this is more a philosophical question. Heathfield's viewpoint
is perfectly acceptable if you say:
Usability is less valuable than portability.
As he said, performance wasn't a concern for his software.
Portability was.
Result?
A mediocre but perfectly portable software.
And guess what? Most of the blowhards in this group write SW which never
gets ported anywhere anyway.
Richard wrote:
And guess what? Most of the blowhards in this group write SW which never
gets ported anywhere anyway.
Umm - before you make a statement like that you might want to
check with some of those blowhards who make some of their C
source code available for free download...
....and on the other hand, you might prefer to not know.
;-)
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA http://www.iedu.com/DeSoto/
"Bartc" <bc@freeuk.comw rote in message
news:Y6******** *********@text. news.virginmedi a.com...
From an article about implementing a C99 to C90 translator...
How does someone use integer arithmetic of at least 64 bits, and write in
pure C90?
As I understand C90 (the standard is very elusive), long int is guaranteed
to be at least 32 bits only.
So, do people rely on their known compiler limits, use clunky emulations,
or do not bother with 64 bits when writing ultra-portable code?
OK, so for this to be practical, such a translator needs to know the
capabilities of a C90 installation. If it has 64+ bit ints, then use them,
otherwise make other arrangements. A pure translator would be of academic
interest only.
Attend to 1000 other details and such a translator may be feasible.
(Note: I am not creating such a software, just interested in the issues.)
--
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