Re: [PATCH 2/15 v2] Unhardcode byte size being 8 bits.

[David Given <dg@cowlark.com>]

[-- Attachment #1: Type: text/plain, Size: 1562 bytes --]

Alexey Zaytsev wrote:
[...]
> This problem may be addressed by changing bits_to_bytes to
> static inline int bits_to_bytes(int bits)
> {
>        return bits >= 0 ? bits / bits_in_char : -1;
> }

That's fine by me (although I've been using my version for ages now with
no apparent problems --- just out of interest, Clue is now using Sparse
to compile C into Lua, Javascript, Perl 5, Common Lisp, C and Java
moderately successfully).

> But it seems there is also a bug in sparse, as in
> ctype_declaration[] the bit_size of void_ctype is
> set to NULL, while gcc assumes sizeof(void) being 1.
> Currently sparse would generate wrong code for:
[...]
> unsigned long test1(void *p)
> {
>         return sizeof(*p);
> }

TBH, I don't think that's legal --- I know of several compilers that
will refuse to compile it, and gcc -pedantic produces a warning, which
means it probably falls into the 'undefined behaviour' bucket of the
standard. I can't find anything that specifically talks about sizeof
void, but 6.3.2.2.1 prohibits doing *anything* with the result of an
expression of type void, which sort of applies here.

Of course, I'm thinking about this from the sparse-as-a-compiler point
of view, where you're probably more interested in replicating gcc's
behaviour.

-- 
┌─── ｄｇ＠ｃｏｗｌａｒｋ．ｃｏｍ ───── http://www.cowlark.com ─────
│ "A line dancer near a graduated cylinder, the blithe spirit inside
│ some wheelbarrow, and a tomato are what made America great!" --=