On Fri, Feb 17, 2006 at 04:40:08PM -0700, Travis Oliphant wrote:

What is PY_SSIZE_T_MAX supposed to be? The definition in pyport.h doesn't compile.

Why not? Does it give an error for your particular platform? What platform is that? What are HAVE_SSIZE_T, SIZEOF_VOID_P and SIZEOF_SIZE_T defined to be? While looking at the piece of code in Include/pyport.h I do notice that the fallback (when ssize_t is not available) is to Py_uintptr_t... Which is an unsigned type, while ssize_t is supposed to be signed. Martin, is that on purpose? I don't have any systems that lack ssize_t. ;P That should prevent the PY_SSIZE_T_MAX definition from compiling though.

Shouldn't a lot of checks for INT_MAX be replaced with PY_SSIZE_T_MAX? Like in the slice indexing code?

Yes, ideally. (Actually, I think slice indexing was changed earlier today.) But while changing it would have little to no effect on 32-bit machines, doing it the wrong way may break the code on 64-bit machines in subtle ways, so it's not all done blindly, or in one big shot. Also, because some output parameters to PyArg_ParsE* change size (s#/t#), code will have to be reviewed to make use of the full address range anyway. (There's some preprocessor hackery that checks for PY_SIZE_T_CLEAN to see if it's safe to use the large output versions.) Adapting all code in the right way isn't finished yet (not in the last place because some of the code is... how shall I put it... 'creative'.) -- Thomas Wouters <thomas@xs4all.net> Hi! I'm a .signature virus! copy me into your .signature file to help me spread!

[Travis Oliphant]

Maybe I have the wrong version of code. In my pyport.h (checked out from svn trunk) I have.

#define PY_SSIZE_T_MAX ((Py_ssize_t)(((size_t)-1)>>1))

What is size_t?

size_t is an unsigned integral type defined by, required by, and used all over the place in standard C. What exactly is the compiler message you get, and exactly which compiler are you using (note that nobody else is having problems with this, so there's something unique in your setup)?

Is this supposed to be sizeof(size_t)?

No. (size_t)-1 casts -1 to the unsigned integral type size_t, which creates a "solid string of 1 bits" with the width of the size_t type. ">> 1" then shifts that right one bit, clearing the sign bit but leaving the rest of the integer "all 1s". Then that's cast to type Py_ssize_t, which is a signed integral type with the same width as the standard size_t. In the end, you get the largest positive signed integer with the same width as size_t, and that's the intent.

I get a syntax error when I actually use PY_SSIZE_T_MAX somewhere in the code.

Nobody else does (PY_SSIZE_T_MAX is referenced in a few places already), so you need to give more information. Is it simply that you neglected to include Python.h in some extension module? The definition of size_t must be (according to the C standard) supplied by stdlib.h, and Python.h includes stdlib.h. It's also possible the some core Python C code doesn't #include enough stuff to get the platform's size_t definition.

On 2/17/06, Travis E. Oliphant <oliphant.travis@ieee.org> wrote:

I'm very sorry for my silliness. I do see the problem I was having now. Thank you for helping me out. I was assuming that PY_SSIZE_T_MAX could be used in a pre-processor statement like LONG_MAX and INT_MAX.

In other words

#if PY_SSIZE_T_MAX != INT_MAX

I suppose that might be nice, but would require configure magic. I'm not sure how it could be done on Windows. There are much more important problems to address at this point IMO. Just review the recent fixes related to Py_BuildValue() on python-checkins to see what I mean. n

Martin v. Löwis wrote:

Neal Norwitz wrote:

...

I suppose that might be nice, but would require configure magic. I'm not sure how it could be done on Windows.

Contributions are welcome. On Windows, it can be hard-coded.

Actually, something like

#if SIZEOF_SIZE_T == SIZEOF_INT #define PY_SSIZE_T_MAX INT_MAX #elif SIZEOF_SIZE_T == SIZEOF_LONG #define PY_SSIZE_T_MAX LONG_MAX #else #error What is size_t equal to? #endif

might work.

Why not just #if SIZEOF_SIZE_T == 2 #define PY_SSIZE_T_MAX 0x7fff #elif SIZEOF_SIZE_T == 4 #define PY_SSIZE_T_MAX 0x7fffffff #elif SIZEOF_SIZE_T == 8 #define PY_SSIZE_T_MAX 0x7fffffffffffffff #elif SIZEOF_SIZE_T == 16 #define PY_SSIZE_T_MAX 0x7fffffffffffffffffffffffffffffff #endif ?