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* Define macros for handling SIGFPE.
* Lee Busby, LLNL, November, 1996
*********************************************
* Overview of the system for handling SIGFPE:
* This file (Include/pyfpe.h) defines a couple of "wrapper" macros for
* insertion into your Python C code of choice. Their proper use is
* discussed below. The file Python/pyfpe.c defines a pair of global
* variables PyFPE_jbuf and PyFPE_counter which are used by the signal
* handler for SIGFPE to decide if a particular exception was protected
* by the macros. The signal handler itself, and code for enabling the
* generation of SIGFPE in the first place, is in a (new) Python module
* named fpectl. This module is standard in every respect. It can be loaded
* either statically or dynamically as you choose, and like any other
* Python module, has no effect until you import it.
* In the general case, there are three steps toward handling SIGFPE in any
* 1) Add the *_PROTECT macros to your C code as required to protect
* dangerous floating point sections.
* 2) Turn on the inclusion of the code by adding the ``--with-fpectl''
* flag at the time you run configure. If the fpectl or other modules
* which use the *_PROTECT macros are to be dynamically loaded, be
* sure they are compiled with WANT_SIGFPE_HANDLER defined.
* 3) When python is built and running, import fpectl, and execute
* fpectl.turnon_sigfpe(). This sets up the signal handler and enables
* generation of SIGFPE whenever an exception occurs. From this point
* on, any properly trapped SIGFPE should result in the Python
* FloatingPointError exception.
* Step 1 has been done already for the Python kernel code, and should be
* done soon for the NumPy array package. Step 2 is usually done once at
* python install time. Python's behavior with respect to SIGFPE is not
* changed unless you also do step 3. Thus you can control this new
* facility at compile time, or run time, or both.
********************************
* Using the macros in your code:
* static PyObject *foobar(PyObject *self,PyObject *args)
* PyFPE_START_PROTECT("Error in foobar", return 0)
* result = dangerous_op(somearg1, somearg2, ...);
* PyFPE_END_PROTECT(result)
* If a floating point error occurs in dangerous_op, foobar returns 0 (NULL),
* after setting the associated value of the FloatingPointError exception to
* "Error in foobar". ``Dangerous_op'' can be a single operation, or a block
* of code, function calls, or any combination, so long as no alternate
* return is possible before the PyFPE_END_PROTECT macro is reached.
* The macros can only be used in a function context where an error return
* can be recognized as signaling a Python exception. (Generally, most
* functions that return a PyObject * will qualify.)
* Guido's original design suggestion for PyFPE_START_PROTECT and
* PyFPE_END_PROTECT had them open and close a local block, with a locally
* defined jmp_buf and jmp_buf pointer. This would allow recursive nesting
* of the macros. The Ansi C standard makes it clear that such local
* variables need to be declared with the "volatile" type qualifier to keep
* setjmp from corrupting their values. Some current implementations seem
* to be more restrictive. For example, the HPUX man page for setjmp says
* Upon the return from a setjmp() call caused by a longjmp(), the
* values of any non-static local variables belonging to the routine
* from which setjmp() was called are undefined. Code which depends on
* such values is not guaranteed to be portable.
* I therefore decided on a more limited form of nesting, using a counter
* variable (PyFPE_counter) to keep track of any recursion. If an exception
* occurs in an ``inner'' pair of macros, the return will apparently
* come from the outermost level.
#ifdef WANT_SIGFPE_HANDLER
extern jmp_buf PyFPE_jbuf;
extern int PyFPE_counter;
extern double PyFPE_dummy(void *);
#define PyFPE_START_PROTECT(err_string, leave_stmt) \
if (!PyFPE_counter++ && setjmp(PyFPE_jbuf)) { \
PyErr_SetString(PyExc_FloatingPointError, err_string); \
* This (following) is a heck of a way to decrement a counter. However,
* unless the macro argument is provided, code optimizers will sometimes move
* this statement so that it gets executed *before* the unsafe expression
* which we're trying to protect. That pretty well messes things up,
* If the expression(s) you're trying to protect don't happen to return a
* value, you will need to manufacture a dummy result just to preserve the
* correct ordering of statements. Note that the macro passes the address
* of its argument (so you need to give it something which is addressable).
* If your expression returns multiple results, pass the last such result
* Note that PyFPE_dummy returns a double, which is cast to int.
* This seeming insanity is to tickle the Floating Point Unit (FPU).
* If an exception has occurred in a preceding floating point operation,
* some architectures (notably Intel 80x86) will not deliver the interrupt
* until the *next* floating point operation. This is painful if you've
* already decremented PyFPE_counter.
#define PyFPE_END_PROTECT(v) PyFPE_counter -= (int)PyFPE_dummy(&(v));
#define PyFPE_START_PROTECT(err_string, leave_stmt)
#define PyFPE_END_PROTECT(v)
It is recommended that you Edit text format, this type of Fix handles quite a lot in one request
