Apparatus for performing modal interval calculations based on decoration configuration

1. Apparatus for calculating a result modal interval dependent on a first modal interval, a second modal interval and a third modal interval, the first modal interval defined by a first endpoint pair, the second modal interval defined by a second endpoint pair, the third modal interval defined by a third endpoint pair, the result modal interval defined by a result endpoint pair, each endpoint of the endpoint pair of each of the first, second, third and result modal intervals characterized by sign, fraction, and exponent bit fields, the apparatus comprising:

a. a first operand register for holding endpoints of the first endpoint pair of the first modal interval, and for providing a first operand signal specifying contents of the bit fields of the endpoints of the first endpoint pair of the first modal interval;

b. a second operand register for holding endpoints of the second endpoint pair of the second modal interval, and for providing a second operand signal specifying contents of the bit fields of the endpoints of the second endpoint pair of the second modal interval;

c. a third operand register for holding endpoints of the third endpoint pair of the third modal interval, and for providing a third operand signal specifying contents of the bit fields of the endpoints of the third endpoint pair of the third modal interval;

d. an analysis element for receiving the first, second and third operand signals and creating a first, second and third truth table pair, respectively, from the first, second and third endpoint pair, each truth table pair comprising a first and second truth table, respectively, for the first and second endpoint of the endpoint pair, each truth table including a sign bit (S) indicating the sign of the respective endpoint, a not-a-number bit (N) indicating whether the respective endpoint is Not-a-Number, an infinity bit (I) indicating whether the respective endpoint is infinity, and a zero bit (Z) indicating whether the respective endpoint is zero;

e. a classification element for determining a first classification from the first truth table pair, a second classification from the second truth table pair, and a third classification from the third truth table pair, each classification including an empty bit (E) and a tracking decoration (T), wherein:

i. when the truth table pair indicates the respective endpoints have the same sign and magnitudes of infinity, the empty bit is 1 and the tracking decoration indicates an empty or non-empty restriction;

ii. when the truth table pair indicates exactly one of the respective endpoints is not-a-number, the empty bit is 1 and the tracking decoration is the NaN decoration field from the not-a-number endpoint;

iii. when the truth table pair indicates both respective endpoints are not-a-number, the empty bit is 1 and the tracking decoration indicates a select restriction;

iv. otherwise, the empty bit is 0 and the tracking decoration is not used; and,

f. providing a result signal encoding the result modal interval, wherein:

i. when the empty bit from the first classification is 1, the empty bit from the second classification is 1, and the empty bit from the third classification is 1, the result modal interval is a decorated empty set encoding the tracking decoration of minimum value from the first, second and third classification;

ii. when the empty bit from the first classification is 1, the empty bit from the second classification is 1, and the empty bit from the third classification is 0, the result modal interval is a decorated empty set encoding the tracking decoration of minimum value from the first and second classification;

iii. when the empty bit from the first classification is 1, the empty bit from the second classification is 0, and the empty bit from the third classification is 1, the result modal interval is a decorated empty set encoding the tracking decoration of minimum value from the first and third classification;

iv. when the empty bit from the first classification is 1, the empty bit from the second classification is 0, and the empty bit from the third classification is 0, the result modal interval is a decorated empty set encoding the tracking decoration of the first classification;

v. when the empty bit from the first classification is 0, the empty bit from the second classification is 1, and the empty bit from the third classification is 1, the result modal interval is a decorated empty set encoding the tracking decoration of minimum value from the second and third classification;

vi. when the empty bit from the first classification is 0, the empty bit from the second classification is 1, and the empty bit from the third classification is 0, the result modal interval is a decorated empty set encoding the tracking decoration of the second classification;

vii. when the empty bit from the first classification is 0, the empty bit from the second classification is 0, and the empty bit from the third classification is 1, the result modal interval is a decorated empty set encoding the tracking decoration of the third classification;

viii. when the empty bit from the first classification is 0, the empty bit from the second classification is 0, and the empty bit from the third classification is 0, the result modal interval is a result of a computation by a computational element receiving the first, second and third operand signals and the first, second and third truth table pairs.

2. The apparatus of claim 1 , wherein the analysis element creates the truth tables dependent on a preselected exponent field bit configuration in each of the respective endpoints, and on a preselected fraction field bit configuration in each of the respective endpoints.

3. The apparatus of claim 1 , wherein said computational element comprises a structure for computing a ternary modal interval operation.

4. The apparatus of claim 3 wherein said ternary modal interval operation is a fused modal interval operation.

5. The apparatus of claim 4 wherein said fused modal interval operation is a fused multiply-add modal interval operation.

6. The apparatus of claim 4 wherein said fused modal interval operation is a fused multiply-subtract modal interval operation.

7. The apparatus of claim 4 wherein said fused modal interval operation is a fused subtract-multiply modal interval operation.

8. The apparatus of claim 4 wherein said fused modal interval operation requires only a single outward digital rounding.