#ifndef Py_PYFPE_H

#define Py_PYFPE_H

#ifdef __cplusplus

extern "C" {

#endif

/*

     ---------------------------------------------------------------------  

    /                       Copyright (c) 1996.                           \ 

   |          The Regents of the University of California.                 |

   |                        All rights reserved.                           |

   |                                                                       |

   |   Permission to use, copy, modify, and distribute this software for   |

   |   any purpose without fee is hereby granted, provided that this en-   |

   |   tire notice is included in all copies of any software which is or   |

   |   includes  a  copy  or  modification  of  this software and in all   |

   |   copies of the supporting documentation for such software.           |

   |                                                                       |

   |   This  work was produced at the University of California, Lawrence   |

   |   Livermore National Laboratory under  contract  no.  W-7405-ENG-48   |

   |   between  the  U.S.  Department  of  Energy and The Regents of the   |

   |   University of California for the operation of UC LLNL.              |

   |                                                                       |

   |                              DISCLAIMER                               |

   |                                                                       |

   |   This  software was prepared as an account of work sponsored by an   |

   |   agency of the United States Government. Neither the United States   |

   |   Government  nor the University of California nor any of their em-   |

   |   ployees, makes any warranty, express or implied, or  assumes  any   |

   |   liability  or  responsibility  for the accuracy, completeness, or   |

   |   usefulness of any information,  apparatus,  product,  or  process   |

   |   disclosed,   or  represents  that  its  use  would  not  infringe   |

   |   privately-owned rights. Reference herein to any specific  commer-   |

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   |   imply  its endorsement, recommendation, or favoring by the United   |

   |   States Government or the University of California. The views  and   |

   |   opinions  of authors expressed herein do not necessarily state or   |

   |   reflect those of the United States Government or  the  University   |

   |   of  California,  and shall not be used for advertising or product   |

    \  endorsement purposes.                                              / 

     ---------------------------------------------------------------------  

*/

/*

 *       Define macros for handling SIGFPE.

 *       Lee Busby, LLNL, November, 1996

 *       busby1@llnl.gov

 * 

 *********************************************

 * Overview of the system for handling SIGFPE:

 * 

 * This file (Include/pyfpe.h) defines a couple of "wrapper" macros for

 * insertion into your Python C code of choice. Their proper use is

 * discussed below. The file Python/pyfpe.c defines a pair of global

 * variables PyFPE_jbuf and PyFPE_counter which are used by the signal

 * handler for SIGFPE to decide if a particular exception was protected

 * by the macros. The signal handler itself, and code for enabling the

 * generation of SIGFPE in the first place, is in a (new) Python module

 * named fpectl. This module is standard in every respect. It can be loaded

 * either statically or dynamically as you choose, and like any other

 * Python module, has no effect until you import it.

 * 

 * In the general case, there are three steps toward handling SIGFPE in any

 * Python code:

 * 

 * 1) Add the *_PROTECT macros to your C code as required to protect

 *    dangerous floating point sections.

 * 

 * 2) Turn on the inclusion of the code by adding the ``--with-fpectl''

 *    flag at the time you run configure.  If the fpectl or other modules

 *    which use the *_PROTECT macros are to be dynamically loaded, be

 *    sure they are compiled with WANT_SIGFPE_HANDLER defined.

 * 

 * 3) When python is built and running, import fpectl, and execute

 *    fpectl.turnon_sigfpe(). This sets up the signal handler and enables

 *    generation of SIGFPE whenever an exception occurs. From this point

 *    on, any properly trapped SIGFPE should result in the Python

 *    FloatingPointError exception.

 * 

 * Step 1 has been done already for the Python kernel code, and should be

 * done soon for the NumPy array package.  Step 2 is usually done once at

 * python install time. Python's behavior with respect to SIGFPE is not

 * changed unless you also do step 3. Thus you can control this new

 * facility at compile time, or run time, or both.

 * 

 ******************************** 

 * Using the macros in your code:

 * 

 * static PyObject *foobar(PyObject *self,PyObject *args)

 * {

 *     ....

 *     PyFPE_START_PROTECT("Error in foobar", return 0)

 *     result = dangerous_op(somearg1, somearg2, ...);

 *     PyFPE_END_PROTECT(result)

 *     ....

 * }

 * 

 * If a floating point error occurs in dangerous_op, foobar returns 0 (NULL),

 * after setting the associated value of the FloatingPointError exception to

 * "Error in foobar". ``Dangerous_op'' can be a single operation, or a block

 * of code, function calls, or any combination, so long as no alternate

 * return is possible before the PyFPE_END_PROTECT macro is reached.

 * 

 * The macros can only be used in a function context where an error return

 * can be recognized as signaling a Python exception. (Generally, most

 * functions that return a PyObject * will qualify.)

 * 

 * Guido's original design suggestion for PyFPE_START_PROTECT and

 * PyFPE_END_PROTECT had them open and close a local block, with a locally

 * defined jmp_buf and jmp_buf pointer. This would allow recursive nesting

 * of the macros. The Ansi C standard makes it clear that such local

 * variables need to be declared with the "volatile" type qualifier to keep

 * setjmp from corrupting their values. Some current implementations seem

 * to be more restrictive. For example, the HPUX man page for setjmp says

 * 

 *   Upon the return from a setjmp() call caused by a longjmp(), the

 *   values of any non-static local variables belonging to the routine

 *   from which setjmp() was called are undefined. Code which depends on

 *   such values is not guaranteed to be portable.

 * 

 * I therefore decided on a more limited form of nesting, using a counter

 * variable (PyFPE_counter) to keep track of any recursion.  If an exception

 * occurs in an ``inner'' pair of macros, the return will apparently

 * come from the outermost level.

 * 

 */

#ifdef WANT_SIGFPE_HANDLER

#include <signal.h>

#include <setjmp.h>

#include <math.h>

extern jmp_buf PyFPE_jbuf;

extern int PyFPE_counter;

extern double PyFPE_dummy(void *);

#define PyFPE_START_PROTECT(err_string, leave_stmt) \

if (!PyFPE_counter++ && setjmp(PyFPE_jbuf)) { \

	PyErr_SetString(PyExc_FloatingPointError, err_string); \

	PyFPE_counter = 0; \

	leave_stmt; \

}

/*

 * This (following) is a heck of a way to decrement a counter. However,

 * unless the macro argument is provided, code optimizers will sometimes move

 * this statement so that it gets executed *before* the unsafe expression

 * which we're trying to protect.  That pretty well messes things up,

 * of course.

 * 

 * If the expression(s) you're trying to protect don't happen to return a

 * value, you will need to manufacture a dummy result just to preserve the

 * correct ordering of statements.  Note that the macro passes the address

 * of its argument (so you need to give it something which is addressable).

 * If your expression returns multiple results, pass the last such result

 * to PyFPE_END_PROTECT.

 * 

 * Note that PyFPE_dummy returns a double, which is cast to int.

 * This seeming insanity is to tickle the Floating Point Unit (FPU).

 * If an exception has occurred in a preceding floating point operation,

 * some architectures (notably Intel 80x86) will not deliver the interrupt

 * until the *next* floating point operation.  This is painful if you've

 * already decremented PyFPE_counter.

 */

#define PyFPE_END_PROTECT(v) PyFPE_counter -= (int)PyFPE_dummy(&(v));

#else

#define PyFPE_START_PROTECT(err_string, leave_stmt)

#define PyFPE_END_PROTECT(v)

#endif

#ifdef __cplusplus

}

#endif

#endif /* !Py_PYFPE_H */