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1 | #ifndef Py_PYFPE_H |
2 | #define Py_PYFPE_H | |
3 | #ifdef __cplusplus | |
4 | extern "C" { | |
5 | #endif | |
6 | /* | |
7 | --------------------------------------------------------------------- | |
8 | / Copyright (c) 1996. \ | |
9 | | 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 | | |
27 | | Government nor the University of California nor any of their em- | | |
28 | | ployees, makes any warranty, express or implied, or assumes any | | |
29 | | liability or responsibility for the accuracy, completeness, or | | |
30 | | usefulness of any information, apparatus, product, or process | | |
31 | | disclosed, or represents that its use would not infringe | | |
32 | | privately-owned rights. Reference herein to any specific commer- | | |
33 | | cial products, process, or service by trade name, trademark, | | |
34 | | manufacturer, or otherwise, does not necessarily constitute or | | |
35 | | imply its endorsement, recommendation, or favoring by the United | | |
36 | | States Government or the University of California. The views and | | |
37 | | opinions of authors expressed herein do not necessarily state or | | |
38 | | reflect those of the United States Government or the University | | |
39 | | of California, and shall not be used for advertising or product | | |
40 | \ endorsement purposes. / | |
41 | --------------------------------------------------------------------- | |
42 | */ | |
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 | * | |
69 | * 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. | |
73 | * | |
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 | * | |
80 | * 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. | |
85 | * | |
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) | |
93 | * result = dangerous_op(somearg1, somearg2, ...); | |
94 | * PyFPE_END_PROTECT(result) | |
95 | * .... | |
96 | * } | |
97 | * | |
98 | * 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. | |
103 | * | |
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 | |
124 | * come from the outermost level. | |
125 | * | |
126 | */ | |
127 | ||
128 | #ifdef WANT_SIGFPE_HANDLER | |
129 | #include <signal.h> | |
130 | #include <setjmp.h> | |
131 | #include <math.h> | |
132 | extern jmp_buf PyFPE_jbuf; | |
133 | extern int PyFPE_counter; | |
134 | extern double PyFPE_dummy(void *); | |
135 | ||
136 | #define PyFPE_START_PROTECT(err_string, leave_stmt) \ | |
137 | if (!PyFPE_counter++ && setjmp(PyFPE_jbuf)) { \ | |
138 | PyErr_SetString(PyExc_FloatingPointError, err_string); \ | |
139 | PyFPE_counter = 0; \ | |
140 | leave_stmt; \ | |
141 | } | |
142 | ||
143 | /* | |
144 | * This (following) is a heck of a way to decrement a counter. However, | |
145 | * 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. | |
163 | */ | |
164 | #define PyFPE_END_PROTECT(v) PyFPE_counter -= (int)PyFPE_dummy(&(v)); | |
165 | ||
166 | #else | |
167 | ||
168 | #define PyFPE_START_PROTECT(err_string, leave_stmt) | |
169 | #define PyFPE_END_PROTECT(v) | |
170 | ||
171 | #endif | |
172 | ||
173 | #ifdef __cplusplus | |
174 | } | |
175 | #endif | |
176 | #endif /* !Py_PYFPE_H */ |