Evaluation of Intrinsic Procedures


       To:    J3
       From:  Craig Dedo
       Date:  May 31, 2000
          Subject:  Interpretation 12 - Evaluation of Intrinsic Procedures

            NUMBER:     000012
            TITLE:      Evaluation of Intrinsic Procedures
          KEYWORDS: Algorithm, Mathematical, Computational
               DEFECT TYPE:   Interpretation
            STATUS:     J3 Consideration in Progress

QUESTION:
     1.   When the standard specifies an algorithm for computing a mathematical procedure, must a processor use the
     specified algorithm?

          Example:  ANINT is defined as INT (A + 0.5).  On some processors ANINT (16 000 001.0) evaluates to
          16 000 002.0 using this algorithm.

2.   May a processor return a mathematically equivalent result in the evaluation of a numeric intrinsic procedure?

          Example:  If ANINT (16 000 001.0) can be computed as the more expected 16 000 001.0, may a processor do so?

ANSWER:
1.   No, a processor is not required to use the algorithm from the standard.

2.   Yes, a processor may return the mathematically equivalent result in the evaluation of any numeric intrinsic
procedure.

DISCUSSION:

The use of an algorithm in the definitions for intrinsic procedures is intended to describe the end result.  It is not
intended to require that a processor use a particular method of achieving that result.  Thus, an algorithm specifies
the mathematical results, not the computational results, of the evaluation of intrinsic procedures.

This standard does not require a processor to use a particular accuracy or precision.  Section 1.4, "Exclusions",
states in part:
    "This standard does not specify: . . .
               (6)  The physical properties of the representation of quantities and the method of rounding,
          approximating, or computing numeric values on a particular processor." [1:26, 1:37-38]

       EDITS: None.

               SUBMITTED BY:  Keith H. Bierman

                         HISTORY:  95-247r1  m134 Submitted as F90 interp 000202 with proposed response, approved 9-4,
                         subsumes F90 interp 000200.
                             95-256    m134 Ballot failed, 10-6
                             95-260    m135 Proposed response, no action
                             96-023    m136 Proposed response, no action
                             96-054    m137 Proposed response, no action
                             96-117    m138 Proposed response, no action
                             97-259r1  m143 Re-submitted as F95 interp 000012 with proposed response
                             00-214    m153 Proposed response

[End of J3 / 00-214]