Echelon LonTal Stack Uživatelský manuál stáhnout pdf (Strana 111)

LonTalk Stack Developer’s Guide 99

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The float_type structure declaration represents a floating-point number in IEEE

754 single-precision format. This format has one sign bit, eight exponent bits,

and 23 mantissa bits; the data is stored in big-endian order. The float_type type

is identical to the type used to represent floating-point network variables.

For example, the LonTalk Interface Developer utility generates the following

definitions for the floating point type SNVT_volt_f:

* Type: SNVT_volt_f

typedef LON_STRUCT_BEGIN(SNVT_volt_f)

{

LonByte Flags_1; /* Use bit field macros, defined

below */

LonByte Flags_2; /* Use bit field macros, defined

below */

ncuLong LS_mantissa;

} LON_STRUCT_END(SNVT_volt_f);

* Macros to access the sign bit field contained in

* Flags_1

#define LON_SIGN_MASK 0x80

#define LON_SIGN_SHIFT 7

#define LON_SIGN_FIELD Flags_1

* Macros to access the MS_exponent bit field contained in

* Flags_1

#define LON_MSEXPONENT_MASK 0x7F

#define LON_MSEXPONENT_SHIFT 0

#define LON_MSEXPONENT_FIELD Flags_1

* Macros to access the LS_exponent bit field contained in

* Flags_2

#define LON_LSEXPONENT_MASK 0x80

#define LON_LSEXPONENT_SHIFT 7

#define LON_LSEXPONENT_FIELD Flags_2

* Macros to access the MS_mantissa bit field contained in

* Flags_2

#define LON_MSMANTISSA_MASK 0x7F

#define LON_MSMANTISSA_SHIFT 0

#define LON_MSMANTISSA_FIELD Flags_2

See the IEEE Standard for Binary Floating-Point Arithmetic (ANSI/IEEE Std

754-1985) documentation for more information.

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Echelon LonTal Stack Uživatelský manuál Strana 111