Echelon Neuron C - Manual (Page 79)

Neuron C Reference Guide 59
float_type X, A, B, C;
fl_mul(&B, &C, &X);
fl_add(&X, &A, &X);
The floating-point format can represent numbers in the range of approximately -
1*10
1038 to +1*10 1038 , with a relative resolution of approximately ±1*10 -7 .
A float_type structure data type is defined by means of a typedef in the <float.h>
file. It defines a structure that represents a floating-point number in IEEE 754
single precision format. This has one sign bit, eight exponent bits and 23
mantissa bits, and is stored in big-endian order. Processors that store data in
little-endian order represent IEEE 754 numbers in the reverse byte order. The
float_type type is identical to the type used to represent floating-point network
variables. The type declaration is shown here for reference.
typedef struct {
unsigned int sign
: 1;
// 0 = positive, 1 = negative
unsigned int MS_exponent : 7;
unsigned int LS_exponent : 1;
unsigned int MS_mantissa : 7;
unsigned long LS_mantissa;
} float_type;
See the IEEE 754 standard documentation for more details.
All the constants and functions in the <float.h> file are defined using the
Neuron C float_type floating-point format, which is a structure. Neuron C does
not permit structures to be passed as parameters or returned as values from
functions. When these objects are passed as parameters to C functions, they are
passed as addresses (using the '&' operator) rather than as values. However,
Neuron C does support structure assignment, so floating-point objects can be
assigned to each other with the '=' assignment operator.
An fl_error global variable stores the last error detected by the floating-point
functions. If error detection is desired for a calculation, application programs
should set the fl_error variable to FL_OK before beginning a series of floating-
point operations, and check the value of the variable at the end.
The errors detected are as follows:
FL_UNDERFLOW A non-zero number could not be represented
because it was too small for the floating-point
representation. Zero was returned instead.
FL_INVALID_ARG A floating-point number could not be converted
to integer because it was out of range; or, an
attempt was made to evaluate the square root
of a negative number.
FL_OVERFLOW A number could not be represented because it
was too large for the floating-point
representation.
FL_DIVIDE_BY_ZERO An attempt was made to divide by zero. This
does not cause the Neuron firmware
DIVIDE_BY_ZERO error to be logged.