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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-   |
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     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   |
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     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 (at) 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