NAME

mathtrap − enable/disable floating-point exception trap

SYNOPSIS

#include <math.h>
int mathtrap(flags)
int flags;

DESCRIPTION

This function sets a flag which enable or disable Floating-point exception traps.  Some constants defined in <math.h> or bitwide logical OR of them are used as Flags.  mathtrap returns previous value of flags. 
The names of constants and exceptions are:

  Exception    <math.h>

Branch/Set on Unordered  FPET_BSUNO
Signaling Not a Number  FPET_SGNAN
Operand Error  FPET_OPERR
Overflow  FPET_OVFLW
Underflow  FPET_UNDFL
Divide by Zero  FPET_DIVZR
Inexact  FPET_INEXA

For example, to enable “Operand Error” and “Divide by Zero” exception traps, call

mathtrap(FPET_OPERR | FPET_DIVZR);

To disable all Floating−point exception traps (this is default status), call

mathtrap(FPET_CLEAR);

To specify IEEE 754 ’s “Invalid Operation”, call

mathtrap(FPET_INVOP);

where FPET_INVOP equals FPET_BSUNO | FPET_SGNAN | FPET_OPERR. 

Trap handler is specified with signal(3) function.  The signal number of all Floating-point exception traps is SIGFPE which is defined in “<signal.h>”.  And signal codes are:

Exception    signal code  (<signal.h>)

Branch/Set on Unordered  FPE_UNORDERED_TRAP
Signaling Not a Number  FPE_SNAN_TRAP
Operand Error  FPE_OPERAND_TRAP
Overflow  FPE_OVERFLOW_TRAP
Underflow  FPE_UNDERFLOW_TRAP
Divide by Zero  FPE_DIVZERO_TRAP
Inexact  FPE_INEXACT_TRAP

A sample trap handler which recognize the kind of exception is shown. 

#include <math.h>
#include <signal.h>
main()
{
int handler();
/∗
∗Set up exception handler
∗/
mathtrap( FPET_INVOP | FPET_OVFLW |
   FPET_DIVZR | FPET_UNDFL  );
signal( SIGFPE  , handler);
.
.
.
}
/∗
∗Exception handler
∗/
handler(sig, code)
int sig, code;
{
switch (code) {
case FPE_UNORDERED_TRAP :
/∗
∗Branch/Set on Unordered TRAP
∗/
break;
case FPE_SNAN_TRAP :
/∗
∗Signaling NaN (Not a Number)
∗/
break;
case FPE_OPERAND_TRAP :
/∗
∗Operand error TRAP
∗/
break;
case FPE_OVERFLOW_TRAP :
/∗
∗Over Flow
∗/
break;
case FPE_UNDERFLOW_TRAP :
/∗
∗Under Flow
∗/
break;
case FPE_DIVZERO_TRAP :
/∗
∗Divide by 0
∗/
break;
case FPE_INEXACT_TRAP :
/∗
∗Inexact TRAP
∗/
break;
}
.
.
.
}

SEE ALSO

MOTOROLA "MC68881/MC68882 Floating−Point Coprocessor User’s Manual"
intro(3), math(3m)

FILES

/usr/include/math.h
/usr/include/signal.h

NOTE

This library function is only supported on CISC NEWS and in the RISC NEWS 68k cross compiler environment. 

NEWS-OSRelease 4.1C