#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 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 #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)) { \ PyErr_SetString(PyExc_FloatingPointError, err_string); \ PyFPE_counter = 0; \ leave_stmt; \ } /* * 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, * of course. * * 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 * to PyFPE_END_PROTECT. * * 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)); #else #define PyFPE_START_PROTECT(err_string, leave_stmt) #define PyFPE_END_PROTECT(v) #endif #ifdef __cplusplus } #endif #endif /* !Py_PYFPE_H */

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