176 lines
8.3 KiB
C
176 lines
8.3 KiB
C
#ifndef Py_PYFPE_H
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#define Py_PYFPE_H
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#ifdef __cplusplus
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extern "C" {
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#endif
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/*
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---------------------------------------------------------------------
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/ Copyright (c) 1996. \
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| The Regents of the University of California. |
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| All rights reserved. |
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| Permission to use, copy, modify, and distribute this software for |
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| any purpose without fee is hereby granted, provided that this en- |
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| tire notice is included in all copies of any software which is or |
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| includes a copy or modification of this software and in all |
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| copies of the supporting documentation for such software. |
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| |
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| This work was produced at the University of California, Lawrence |
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| Livermore National Laboratory under contract no. W-7405-ENG-48 |
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| between the U.S. Department of Energy and The Regents of the |
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| University of California for the operation of UC LLNL. |
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| DISCLAIMER |
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| This software was prepared as an account of work sponsored by an |
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| agency of the United States Government. Neither the United States |
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| Government nor the University of California nor any of their em- |
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| ployees, makes any warranty, express or implied, or assumes any |
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| liability or responsibility for the accuracy, completeness, or |
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| usefulness of any information, apparatus, product, or process |
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| disclosed, or represents that its use would not infringe |
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| privately-owned rights. Reference herein to any specific commer- |
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| cial products, process, or service by trade name, trademark, |
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| manufacturer, or otherwise, does not necessarily constitute or |
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| imply its endorsement, recommendation, or favoring by the United |
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| States Government or the University of California. The views and |
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| opinions of authors expressed herein do not necessarily state or |
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| reflect those of the United States Government or the University |
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| of California, and shall not be used for advertising or product |
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\ endorsement purposes. /
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---------------------------------------------------------------------
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*/
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/*
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* Define macros for handling SIGFPE.
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* Lee Busby, LLNL, November, 1996
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* busby1@llnl.gov
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*
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*********************************************
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* Overview of the system for handling SIGFPE:
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*
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* This file (Include/pyfpe.h) defines a couple of "wrapper" macros for
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* insertion into your Python C code of choice. Their proper use is
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* discussed below. The file Python/pyfpe.c defines a pair of global
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* variables PyFPE_jbuf and PyFPE_counter which are used by the signal
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* handler for SIGFPE to decide if a particular exception was protected
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* by the macros. The signal handler itself, and code for enabling the
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* generation of SIGFPE in the first place, is in a (new) Python module
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* named fpectl. This module is standard in every respect. It can be loaded
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* either statically or dynamically as you choose, and like any other
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* Python module, has no effect until you import it.
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*
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* In the general case, there are three steps toward handling SIGFPE in any
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* Python code:
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*
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* 1) Add the *_PROTECT macros to your C code as required to protect
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* dangerous floating point sections.
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*
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* 2) Turn on the inclusion of the code by adding the ``--with-fpectl''
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* flag at the time you run configure. If the fpectl or other modules
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* which use the *_PROTECT macros are to be dynamically loaded, be
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* sure they are compiled with WANT_SIGFPE_HANDLER defined.
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*
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* 3) When python is built and running, import fpectl, and execute
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* fpectl.turnon_sigfpe(). This sets up the signal handler and enables
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* generation of SIGFPE whenever an exception occurs. From this point
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* on, any properly trapped SIGFPE should result in the Python
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* FloatingPointError exception.
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*
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* Step 1 has been done already for the Python kernel code, and should be
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* done soon for the NumPy array package. Step 2 is usually done once at
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* python install time. Python's behavior with respect to SIGFPE is not
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* changed unless you also do step 3. Thus you can control this new
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* facility at compile time, or run time, or both.
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*
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********************************
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* Using the macros in your code:
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*
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* static PyObject *foobar(PyObject *self,PyObject *args)
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* {
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* ....
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* PyFPE_START_PROTECT("Error in foobar", return 0)
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* result = dangerous_op(somearg1, somearg2, ...);
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* PyFPE_END_PROTECT(result)
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* ....
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* }
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*
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* If a floating point error occurs in dangerous_op, foobar returns 0 (NULL),
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* after setting the associated value of the FloatingPointError exception to
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* "Error in foobar". ``Dangerous_op'' can be a single operation, or a block
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* of code, function calls, or any combination, so long as no alternate
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* return is possible before the PyFPE_END_PROTECT macro is reached.
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*
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* The macros can only be used in a function context where an error return
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* can be recognized as signaling a Python exception. (Generally, most
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* functions that return a PyObject * will qualify.)
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*
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* Guido's original design suggestion for PyFPE_START_PROTECT and
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* PyFPE_END_PROTECT had them open and close a local block, with a locally
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* defined jmp_buf and jmp_buf pointer. This would allow recursive nesting
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* of the macros. The Ansi C standard makes it clear that such local
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* variables need to be declared with the "volatile" type qualifier to keep
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* setjmp from corrupting their values. Some current implementations seem
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* to be more restrictive. For example, the HPUX man page for setjmp says
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*
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* Upon the return from a setjmp() call caused by a longjmp(), the
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* values of any non-static local variables belonging to the routine
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* from which setjmp() was called are undefined. Code which depends on
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* such values is not guaranteed to be portable.
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*
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* I therefore decided on a more limited form of nesting, using a counter
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* variable (PyFPE_counter) to keep track of any recursion. If an exception
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* occurs in an ``inner'' pair of macros, the return will apparently
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* come from the outermost level.
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*
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*/
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#ifdef WANT_SIGFPE_HANDLER
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#include <signal.h>
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#include <setjmp.h>
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#include <math.h>
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extern jmp_buf PyFPE_jbuf;
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extern int PyFPE_counter;
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extern double PyFPE_dummy(void *);
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#define PyFPE_START_PROTECT(err_string, leave_stmt) \
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if (!PyFPE_counter++ && setjmp(PyFPE_jbuf)) { \
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PyErr_SetString(PyExc_FloatingPointError, err_string); \
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PyFPE_counter = 0; \
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leave_stmt; \
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}
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/*
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* This (following) is a heck of a way to decrement a counter. However,
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* unless the macro argument is provided, code optimizers will sometimes move
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* this statement so that it gets executed *before* the unsafe expression
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* which we're trying to protect. That pretty well messes things up,
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* of course.
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*
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* If the expression(s) you're trying to protect don't happen to return a
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* value, you will need to manufacture a dummy result just to preserve the
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* correct ordering of statements. Note that the macro passes the address
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* of its argument (so you need to give it something which is addressable).
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* If your expression returns multiple results, pass the last such result
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* to PyFPE_END_PROTECT.
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*
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* Note that PyFPE_dummy returns a double, which is cast to int.
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* This seeming insanity is to tickle the Floating Point Unit (FPU).
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* If an exception has occurred in a preceding floating point operation,
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* some architectures (notably Intel 80x86) will not deliver the interrupt
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* until the *next* floating point operation. This is painful if you've
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* already decremented PyFPE_counter.
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*/
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#define PyFPE_END_PROTECT(v) PyFPE_counter -= (int)PyFPE_dummy(&(v));
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#else
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#define PyFPE_START_PROTECT(err_string, leave_stmt)
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#define PyFPE_END_PROTECT(v)
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#endif
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#ifdef __cplusplus
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}
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#endif
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#endif /* !Py_PYFPE_H */
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