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author Guido van Rossum <guido@python.org>
date Thu, 17 Jul 1997 16:29:42 +0000
parents f0fd12d76e07
children a00073f2e087
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1 #ifndef Py_PYFPE_H
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2 #define Py_PYFPE_H
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3 #ifdef __cplusplus
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4 extern "C" {
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5 #endif
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6 /*
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7 ---------------------------------------------------------------------
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8 / Copyright (c) 1996. \
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9 | The Regents of the University of California. |
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10 | All rights reserved. |
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11 | |
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12 | Permission to use, copy, modify, and distribute this software for |
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13 | any purpose without fee is hereby granted, provided that this en- |
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14 | tire notice is included in all copies of any software which is or |
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15 | includes a copy or modification of this software and in all |
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16 | copies of the supporting documentation for such software. |
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17 | |
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18 | This work was produced at the University of California, Lawrence |
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19 | Livermore National Laboratory under contract no. W-7405-ENG-48 |
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20 | between the U.S. Department of Energy and The Regents of the |
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21 | University of California for the operation of UC LLNL. |
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22 | |
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23 | DISCLAIMER |
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24 | |
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25 | This software was prepared as an account of work sponsored by an |
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26 | agency of the United States Government. Neither the United States |
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27 | Government nor the University of California nor any of their em- |
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28 | ployees, makes any warranty, express or implied, or assumes any |
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29 | liability or responsibility for the accuracy, completeness, or |
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30 | usefulness of any information, apparatus, product, or process |
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31 | disclosed, or represents that its use would not infringe |
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32 | privately-owned rights. Reference herein to any specific commer- |
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33 | cial products, process, or service by trade name, trademark, |
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34 | manufacturer, or otherwise, does not necessarily constitute or |
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35 | imply its endorsement, recommendation, or favoring by the United |
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36 | States Government or the University of California. The views and |
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37 | opinions of authors expressed herein do not necessarily state or |
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38 | reflect those of the United States Government or the University |
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39 | of California, and shall not be used for advertising or product |
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40 \ endorsement purposes. /
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41 ---------------------------------------------------------------------
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42 */
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43
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44 /*
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45 * Define macros for handling SIGFPE.
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46 * Lee Busby, LLNL, November, 1996
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47 * busby1@llnl.gov
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48 *
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49 *********************************************
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50 * Overview of the system for handling SIGFPE:
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51 *
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52 * This file (Include/pyfpe.h) defines a couple of "wrapper" macros for
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53 * insertion into your Python C code of choice. Their proper use is
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54 * discussed below. The file Python/pyfpe.c defines a pair of global
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55 * variables PyFPE_jbuf and PyFPE_counter which are used by the signal
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56 * handler for SIGFPE to decide if a particular exception was protected
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57 * by the macros. The signal handler itself, and code for enabling the
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58 * generation of SIGFPE in the first place, is in a (new) Python module
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59 * named fpectl. This module is standard in every respect. It can be loaded
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60 * either statically or dynamically as you choose, and like any other
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61 * Python module, has no effect until you import it.
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62 *
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63 * In the general case, there are three steps toward handling SIGFPE in any
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64 * Python code:
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65 *
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66 * 1) Add the *_PROTECT macros to your C code as required to protect
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67 * dangerous floating point sections.
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68 *
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69 * 2) Turn on the inclusion of the code by #defining WANT_SIGFPE_HANDLER in
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70 * config.h.in before you configure, compile, and install Python, and the
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71 * fpectl module, and any other modules which may have conditional code.
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72 *
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73 * 3) When python is built and running, import fpectl, and execute
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74 * fpectl.turnon_sigfpe(). This sets up the signal handler and enables
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75 * generation of SIGFPE whenever an exception occurs. From this point
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76 * on, any properly trapped SIGFPE should result in the Python
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77 * FloatingPointError exception.
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78 *
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79 * Step 1 has been done already for the Python kernel code, and will be
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80 * done soon for Hugunin's NumPy array package and my Gist graphics module.
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81 * Step 2 is usually done once at python install time. Python's behavior
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82 * with respect to SIGFPE is not changed unless you also do step 3. Thus
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83 * you can control this new facility at compile time, or run time, or both.
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84 *
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85 ********************************
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86 * Using the macros in your code:
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87 *
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88 * static PyObject *foobar(PyObject *self,PyObject *args)
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89 * {
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90 * ....
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91 * PyFPE_START_PROTECT("Error in foobar", return 0)
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92 * dangerous_op(somearg1, somearg2, ...);
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93 * PyFPE_END_PROTECT
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94 * ....
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95 * }
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96 *
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97 * If a floating point error occurs in dangerous_op, foobar returns 0
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98 * (NULL), after setting the associated value of the FloatingPointError
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99 * exception to "Error in foobar". ``Dangerous_op'' can be a single
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100 * operation, or a block, or function calls, or any combination, so long as
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101 * no alternate return is possible before the PyFPE_END_PROTECT macro is
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102 * reached.
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103 *
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104 * The macros can only be used in a function context where an error return
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105 * can be recognized as signaling a Python exception. (Generally, most
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106 * functions that return a PyObject * will qualify.)
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107 *
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108 * Guido's original design suggestion for PyFPE_START_PROTECT and
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109 * PyFPE_END_PROTECT had them open and close a local block, with a locally
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110 * defined jmp_buf and jmp_buf pointer. This would allow recursive nesting
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111 * of the macros. The Ansi C standard makes it clear that such local
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112 * variables need to be declared with the "volatile" type qualifier to keep
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113 * setjmp from corrupting their values. Some current implementations seem
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114 * to be more restrictive. For example, the HPUX man page for setjmp says
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115 *
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116 * Upon the return from a setjmp() call caused by a longjmp(), the
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117 * values of any non-static local variables belonging to the routine
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118 * from which setjmp() was called are undefined. Code which depends on
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119 * such values is not guaranteed to be portable.
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120 *
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121 * I therefore decided on a more limited form of nesting, using a counter
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122 * variable (PyFPE_counter) to keep track of any recursion. If an exception
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123 * occurs in an ``inner'' pair of macros, the return will apparently
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124 * come from the top level.
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125 *
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126 */
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127
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128 #ifdef WANT_SIGFPE_HANDLER
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129 #include <signal.h>
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130 #include <setjmp.h>
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131 #include <math.h>
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132 extern jmp_buf PyFPE_jbuf;
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133 extern int PyFPE_counter;
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134 extern double PyFPE_dummy();
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135
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136 #define PyFPE_START_PROTECT(err_string, leave_stmt) \
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137 if (!PyFPE_counter++ && setjmp(PyFPE_jbuf)) { \
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138 PyFPE_counter = 0; \
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139 PyErr_SetString(PyExc_FloatingPointError, err_string); \
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140 leave_stmt; \
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141 }
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142
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143 /*
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144 * This (following) is a heck of a way to decrement a counter. However,
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145 * code optimizers will sometimes move this statement so that it gets
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146 * executed *before* the unsafe expression which we're trying to protect.
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147 * This pretty well messes things up, of course. So the best I've been able
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148 * to do is to put a (hopefully fast) function call into the expression
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149 * which counts down PyFPE_counter, and thereby monkey wrench the overeager
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150 * optimizer. Better solutions are welcomed....
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151 */
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152 #define PyFPE_END_PROTECT(v) PyFPE_counter -= (int)PyFPE_dummy(&(v));
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153
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154 #else
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155
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156 #define PyFPE_START_PROTECT(err_string, leave_stmt)
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157 #define PyFPE_END_PROTECT(v)
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158
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159 #endif
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160
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161 #ifdef __cplusplus
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162 }
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163 #endif
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164 #endif /* !Py_PYFPE_H */