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diff --git a/Include/pyfpe.h b/Include/pyfpe.h new file mode 100644 index 0000000..ef44e66 --- /dev/null +++ b/Include/pyfpe.h @@ -0,0 +1,164 @@ +#ifndef Py_PYFPE_H +#define Py_PYFPE_H +#ifdef __cplusplus +extern "C" { +#endif +/* + --------------------------------------------------------------------- + / Copyright (c) 1996. \ + | The Regents of the University of California. | + | All rights reserved. | + | | + | Permission to use, copy, modify, and distribute this software for | + | any purpose without fee is hereby granted, provided that this en- | + | tire notice is included in all copies of any software which is or | + | includes a copy or modification of this software and in all | + | copies of the supporting documentation for such software. | + | | + | This work was produced at the University of California, Lawrence | + | Livermore National Laboratory under contract no. W-7405-ENG-48 | + | between the U.S. Department of Energy and The Regents of the | + | University of California for the operation of UC LLNL. | + | | + | DISCLAIMER | + | | + | This software was prepared as an account of work sponsored by an | + | agency of the United States Government. Neither the United States | + | Government nor the University of California nor any of their em- | + | ployees, makes any warranty, express or implied, or assumes any | + | liability or responsibility for the accuracy, completeness, or | + | usefulness of any information, apparatus, product, or process | + | disclosed, or represents that its use would not infringe | + | privately-owned rights. Reference herein to any specific commer- | + | cial products, process, or service by trade name, trademark, | + | manufacturer, or otherwise, does not necessarily constitute or | + | imply its endorsement, recommendation, or favoring by the United | + | States Government or the University of California. The views and | + | opinions of authors expressed herein do not necessarily state or | + | reflect those of the United States Government or the University | + | of California, and shall not be used for advertising or product | + \ endorsement purposes. / + --------------------------------------------------------------------- +*/ + +/* + * Define macros for handling SIGFPE. + * Lee Busby, LLNL, November, 1996 + * busby1@llnl.gov + * + ********************************************* + * 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 + * Python code: + * + * 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 #defining WANT_SIGFPE_HANDLER in + * config.h.in before you configure, compile, and install Python, and the + * fpectl module, and any other modules which may have conditional code. + * + * 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 will be + * done soon for Hugunin's NumPy array package and my Gist graphics module. + * 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) + * dangerous_op(somearg1, somearg2, ...); + * PyFPE_END_PROTECT + * .... + * } + * + * 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, or 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 top level. + * + */ + +#ifdef WANT_SIGFPE_HANDLER +#include <signal.h> +#include <setjmp.h> +#include <math.h> +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)) { \ + PyFPE_counter = 0; \ + PyErr_SetString(PyExc_FloatingPointError, err_string); \ + leave_stmt; \ +} + +/* + * This (following) is a heck of a way to decrement a counter. However, + * code optimizers will sometimes move this statement so that it gets + * executed *before* the unsafe expression which we're trying to protect. + * This pretty well messes things up, of course. So the best I've been able + * to do is to put a (hopefully fast) function call into the expression + * which counts down PyFPE_counter, and thereby monkey wrench the overeager + * optimizer. Better solutions are welcomed.... + */ +#define PyFPE_END_PROTECT PyFPE_counter -= (int)PyFPE_dummy(); + +#else + +#define PyFPE_START_PROTECT(err_string, leave_stmt) +#define PyFPE_END_PROTECT + +#endif + +#ifdef __cplusplus +} +#endif +#endif /* !Py_PYFPE_H */ |