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Guido van Rossum7d4266e1997-02-14 22:53:12 +00001#ifndef Py_PYFPE_H
2#define Py_PYFPE_H
3#ifdef __cplusplus
4extern "C" {
5#endif
6/*
Trent Nelson2a0fb142012-08-31 17:11:39 -04007 ---------------------------------------------------------------------
8 / Copyright (c) 1996. \
Guido van Rossum7d4266e1997-02-14 22:53:12 +00009 | The Regents of the University of California. |
10 | All rights reserved. |
11 | |
12 | Permission to use, copy, modify, and distribute this software for |
13 | any purpose without fee is hereby granted, provided that this en- |
14 | tire notice is included in all copies of any software which is or |
15 | includes a copy or modification of this software and in all |
16 | copies of the supporting documentation for such software. |
17 | |
18 | This work was produced at the University of California, Lawrence |
19 | Livermore National Laboratory under contract no. W-7405-ENG-48 |
20 | between the U.S. Department of Energy and The Regents of the |
21 | University of California for the operation of UC LLNL. |
22 | |
23 | DISCLAIMER |
24 | |
25 | This software was prepared as an account of work sponsored by an |
26 | agency of the United States Government. Neither the United States |
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28 | ployees, makes any warranty, express or implied, or assumes any |
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Trent Nelson2a0fb142012-08-31 17:11:39 -040040 \ endorsement purposes. /
41 ---------------------------------------------------------------------
Guido van Rossum7d4266e1997-02-14 22:53:12 +000042*/
43
44/*
45 * Define macros for handling SIGFPE.
46 * Lee Busby, LLNL, November, 1996
47 * busby1@llnl.gov
48 *
49 *********************************************
50 * Overview of the system for handling SIGFPE:
51 *
52 * This file (Include/pyfpe.h) defines a couple of "wrapper" macros for
53 * insertion into your Python C code of choice. Their proper use is
54 * discussed below. The file Python/pyfpe.c defines a pair of global
55 * variables PyFPE_jbuf and PyFPE_counter which are used by the signal
56 * handler for SIGFPE to decide if a particular exception was protected
57 * by the macros. The signal handler itself, and code for enabling the
58 * generation of SIGFPE in the first place, is in a (new) Python module
59 * named fpectl. This module is standard in every respect. It can be loaded
60 * either statically or dynamically as you choose, and like any other
61 * Python module, has no effect until you import it.
62 *
63 * In the general case, there are three steps toward handling SIGFPE in any
64 * Python code:
65 *
66 * 1) Add the *_PROTECT macros to your C code as required to protect
67 * dangerous floating point sections.
68 *
Guido van Rossume85da651997-10-20 23:50:01 +000069 * 2) Turn on the inclusion of the code by adding the ``--with-fpectl''
70 * flag at the time you run configure. If the fpectl or other modules
71 * which use the *_PROTECT macros are to be dynamically loaded, be
72 * sure they are compiled with WANT_SIGFPE_HANDLER defined.
Guido van Rossum7d4266e1997-02-14 22:53:12 +000073 *
74 * 3) When python is built and running, import fpectl, and execute
75 * fpectl.turnon_sigfpe(). This sets up the signal handler and enables
76 * generation of SIGFPE whenever an exception occurs. From this point
77 * on, any properly trapped SIGFPE should result in the Python
78 * FloatingPointError exception.
79 *
Guido van Rossume85da651997-10-20 23:50:01 +000080 * Step 1 has been done already for the Python kernel code, and should be
81 * done soon for the NumPy array package. Step 2 is usually done once at
82 * python install time. Python's behavior with respect to SIGFPE is not
83 * changed unless you also do step 3. Thus you can control this new
84 * facility at compile time, or run time, or both.
Guido van Rossum7d4266e1997-02-14 22:53:12 +000085 *
86 ********************************
87 * Using the macros in your code:
88 *
89 * static PyObject *foobar(PyObject *self,PyObject *args)
90 * {
91 * ....
92 * PyFPE_START_PROTECT("Error in foobar", return 0)
Guido van Rossume85da651997-10-20 23:50:01 +000093 * result = dangerous_op(somearg1, somearg2, ...);
94 * PyFPE_END_PROTECT(result)
Guido van Rossum7d4266e1997-02-14 22:53:12 +000095 * ....
96 * }
97 *
Guido van Rossume85da651997-10-20 23:50:01 +000098 * If a floating point error occurs in dangerous_op, foobar returns 0 (NULL),
99 * after setting the associated value of the FloatingPointError exception to
100 * "Error in foobar". ``Dangerous_op'' can be a single operation, or a block
101 * of code, function calls, or any combination, so long as no alternate
102 * return is possible before the PyFPE_END_PROTECT macro is reached.
Guido van Rossum7d4266e1997-02-14 22:53:12 +0000103 *
104 * The macros can only be used in a function context where an error return
105 * can be recognized as signaling a Python exception. (Generally, most
106 * functions that return a PyObject * will qualify.)
107 *
108 * Guido's original design suggestion for PyFPE_START_PROTECT and
109 * PyFPE_END_PROTECT had them open and close a local block, with a locally
110 * defined jmp_buf and jmp_buf pointer. This would allow recursive nesting
111 * of the macros. The Ansi C standard makes it clear that such local
112 * variables need to be declared with the "volatile" type qualifier to keep
113 * setjmp from corrupting their values. Some current implementations seem
114 * to be more restrictive. For example, the HPUX man page for setjmp says
115 *
116 * Upon the return from a setjmp() call caused by a longjmp(), the
117 * values of any non-static local variables belonging to the routine
118 * from which setjmp() was called are undefined. Code which depends on
119 * such values is not guaranteed to be portable.
120 *
121 * I therefore decided on a more limited form of nesting, using a counter
122 * variable (PyFPE_counter) to keep track of any recursion. If an exception
123 * occurs in an ``inner'' pair of macros, the return will apparently
Guido van Rossume85da651997-10-20 23:50:01 +0000124 * come from the outermost level.
Guido van Rossum7d4266e1997-02-14 22:53:12 +0000125 *
126 */
127
128#ifdef WANT_SIGFPE_HANDLER
129#include <signal.h>
130#include <setjmp.h>
131#include <math.h>
132extern jmp_buf PyFPE_jbuf;
133extern int PyFPE_counter;
Guido van Rossume85da651997-10-20 23:50:01 +0000134extern double PyFPE_dummy(void *);
Guido van Rossum7d4266e1997-02-14 22:53:12 +0000135
136#define PyFPE_START_PROTECT(err_string, leave_stmt) \
137if (!PyFPE_counter++ && setjmp(PyFPE_jbuf)) { \
Guido van Rossum7d4266e1997-02-14 22:53:12 +0000138 PyErr_SetString(PyExc_FloatingPointError, err_string); \
Guido van Rossume85da651997-10-20 23:50:01 +0000139 PyFPE_counter = 0; \
Guido van Rossum7d4266e1997-02-14 22:53:12 +0000140 leave_stmt; \
141}
142
143/*
144 * This (following) is a heck of a way to decrement a counter. However,
Guido van Rossume85da651997-10-20 23:50:01 +0000145 * unless the macro argument is provided, code optimizers will sometimes move
146 * this statement so that it gets executed *before* the unsafe expression
147 * which we're trying to protect. That pretty well messes things up,
148 * of course.
149 *
150 * If the expression(s) you're trying to protect don't happen to return a
151 * value, you will need to manufacture a dummy result just to preserve the
152 * correct ordering of statements. Note that the macro passes the address
153 * of its argument (so you need to give it something which is addressable).
154 * If your expression returns multiple results, pass the last such result
155 * to PyFPE_END_PROTECT.
156 *
157 * Note that PyFPE_dummy returns a double, which is cast to int.
158 * This seeming insanity is to tickle the Floating Point Unit (FPU).
159 * If an exception has occurred in a preceding floating point operation,
160 * some architectures (notably Intel 80x86) will not deliver the interrupt
161 * until the *next* floating point operation. This is painful if you've
162 * already decremented PyFPE_counter.
Guido van Rossum7d4266e1997-02-14 22:53:12 +0000163 */
Guido van Rossum1f06bee1997-03-14 04:23:42 +0000164#define PyFPE_END_PROTECT(v) PyFPE_counter -= (int)PyFPE_dummy(&(v));
Guido van Rossum7d4266e1997-02-14 22:53:12 +0000165
166#else
167
168#define PyFPE_START_PROTECT(err_string, leave_stmt)
Guido van Rossum1f06bee1997-03-14 04:23:42 +0000169#define PyFPE_END_PROTECT(v)
Guido van Rossum7d4266e1997-02-14 22:53:12 +0000170
171#endif
172
173#ifdef __cplusplus
174}
175#endif
176#endif /* !Py_PYFPE_H */