/*FUNCTION<<signal>>---specify handler subroutine for a signalINDEX	signalINDEX	_signal_rINDEX	raiseINDEX	_raise_rANSI_SYNOPSIS	#include <signal.h>	void ( * signal(int <[sig]>, void(*<[func]>)(int)) )(int);	void ( * _signal_r(void *<[reent]>,                            int <[sig]>, void(*<[func]>)(int)) )(int);	int raise (int <[sig]>);	int _raise_r (void *<[reent]>, int <[sig]>);TRAD_SYNOPSIS	#include <signal.h>	char ( * signal(<[sig]>, <[func]>) )()	int <[sig]>;	char ( * <[func]> )();	char ( * _signal_r(<[reent]>, <[sig]>, <[func]>) )()	char *<[reent]>;	int <[sig]>;	char ( * <[func]> )();	int raise (<[sig]>)()	int <[sig]>;	int _raise_r (<[reent]>, <[sig]>)()	char *<[reent]>;	int <[sig]>;DESCRIPTION<<signal, raise>> provide a simple signal/raise implementation for embeddedtargets.<<signal>> allows you to request changed treatment for a particularsignal <[sig]>.  You can use one of the predefined macros <<SIG_DFL>>(select system default handling) or <<SIG_IGN>> (ignore this signal)as the value of <[func]>; otherwise, <[func]> is a function pointerthat identifies a subroutine in your program as the handler for this signal.Some of the execution environment for signal handlers isunpredictable; notably, the only library function required to workcorrectly from within a signal handler is @code{signal} itself, andonly when used to redefine the handler for the current signal value.Static storage is likewise unreliable for signal handlers, with oneexception: if you declare a static storage location as `<<volatilesig_atomic_t>>', then you may use that location in a signal handler tostore signal values.If your signal handler terminates using <<return>> (or implicitreturn), your program's execution continues at the pointwhere it was when the signal was raised (whether by your programitself, or by an external event).  Signal handlers can alsouse functions such as <<exit>> and <<abort>> to avoid returning.<<raise>> sends the signal sig to the executing program.  It returns zero ifsuccessful, non-zero if unsuccessful.The alternate functions <<_signal_r, _raise_r>> are the reentrant versions.The extra argument <[reent]> is a pointer to a reentrancy structure.@c FIXME: do we have setjmp.h and assoc fns?RETURNSIf your request for a signal handler cannot be honored, the result is<<SIG_ERR>>; a specific error number is also recorded in <<errno>>.Otherwise, the result is the previous handler (a function pointer orone of the predefined macros).PORTABILITYANSI C requires <<raise>>, <<signal>>.No supporting OS subroutines are required to link with <<signal>>, butit will not have any useful effects, except for software generated signals,without an operating system that can actually raise exceptions.*//* * signal.c * Original Author:	G. Haley * * signal associates the function pointed to by func with the signal sig. When * a signal occurs, the value of func determines the action taken as follows: * if func is SIG_DFL, the default handling for that signal will occur; if func * is SIG_IGN, the signal will be ignored; otherwise, the default handling for * the signal is restored (SIG_DFL), and the function func is called with sig * as its argument. Returns the value of func for the previous call to signal * for the signal sig, or SIG_ERR if the request fails. *//* _init_signal initialises the signal handlers for each signal. This function   is called by crt0 at program startup.  */#ifdef SIGNAL_PROVIDEDint _dummy_simulated_signal;#else#include <errno.h>#include <signal.h>#include <stddef.h>#include <stdlib.h>#include <reent.h>#include <_syslist.h>int_DEFUN (_init_signal_r, (ptr),	struct _reent *ptr){  int i;  if (ptr->_sig_func == NULL)    {      ptr->_sig_func = (_sig_func_ptr *)_malloc_r (ptr, sizeof (_sig_func_ptr) * NSIG);      if (ptr->_sig_func == NULL)	return -1;      for (i = 0; i < NSIG; i++)	ptr->_sig_func[i] = SIG_DFL;    }  return 0;}_sig_func_ptr_DEFUN (_signal_r, (ptr, sig, func),	struct _reent *ptr _AND	int sig _AND	_sig_func_ptr func){  _sig_func_ptr old_func;  if (sig < 0 || sig >= NSIG)    {      ptr->_errno = EINVAL;      return SIG_ERR;    }  if (ptr->_sig_func == NULL && _init_signal_r (ptr) != 0)    return SIG_ERR;    old_func = ptr->_sig_func[sig];  ptr->_sig_func[sig] = func;  return old_func;}int _raise_r (ptr, sig)     struct _reent *ptr;     int sig;{  _sig_func_ptr func;  if (sig < 0 || sig >= NSIG)    {      ptr->_errno = EINVAL;      return -1;    }  if (ptr->_sig_func == NULL && _init_signal_r (ptr) != 0)    return -1;    func = ptr->_sig_func[sig];  if (func == SIG_DFL)    return _kill_r (ptr, _getpid_r (ptr), sig);  else if (func == SIG_IGN)    return 0;  else if (func == SIG_ERR)    {      ptr->_errno = EINVAL;      return 1;    }  else    {      ptr->_sig_func[sig] = SIG_DFL;      func (sig);      return 0;    }}int__sigtramp_r (ptr, sig)     struct _reent *ptr;     int sig;{  _sig_func_ptr func;  if (sig < 0 || sig >= NSIG)    {      return -1;    }  if (ptr->_sig_func == NULL && _init_signal_r (ptr) != 0)    return -1;  func = ptr->_sig_func[sig];  if (func == SIG_DFL)    return 1;  else if (func == SIG_ERR)    return 2;  else if (func == SIG_IGN)    return 3;  else    {      ptr->_sig_func[sig] = SIG_DFL;      func (sig);      return 0;    }}#ifndef _REENT_ONLYint raise (sig)     int sig;{  return _raise_r (_REENT, sig);}_sig_func_ptr_DEFUN (signal, (sig, func),	int sig _AND	_sig_func_ptr func){  return _signal_r (_REENT, sig, func);}int _init_signal (){  return _init_signal_r (_REENT);}int__sigtramp (int sig){  return __sigtramp_r (_REENT, sig);}#endif#endif /* !SIGNAL_PROVIDED */