Floating-Point Errors

The 8051 does not contain an interrupt vector to trap floating point errors; therefore, your software must appropriately respond to these error conditions.

In addition to the normal floating-point values, a floating-point number may contain a binary error value. These values are defined as a part of the IEEE standard and are used whenever an error occurs during normal processing of floating-point operations. Your code should check for possible arithmetic errors at the end of each floating-point operation.

NOTE

The C51 library function _chkfloat_ allows you to quickly check floating-point status

You can use the following union to store floating-point values.

union f
  {
  float          f;	/* Floating point value */
  unsigned long ul;	/* Unsigned long value */
  };

This union contains a float and an unsigned long in order to perform floating-point math operations and to respond to the IEEE error states. For example:

#define NaN       0xFFFFFFFF    /* Not a number (error) */
#define plusINF   0x7F800000    /* Positive overflow     */
#define minusINF  0xFF800000    /* Negative overflow     */

union f 
  {
  float           f;      /* Floating point value */
  unsigned long   ul;     /* Unsigned long value */
  };


void main (void)
  {
  float a, b;
  union f x;

  x.f = a * b;
  if (x.ul == NaN  || x.ul == plusINF  || x.ul == minusINF)
    {
    /* handle the error  */
    }
  else
    {
    /* result is correct */
    }

}