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   |
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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                               |
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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 */
177