Historically, the term 'builtin' is of course a PL/I one that has been adopted elsewhere too, e.g., by the HLASM. In PL/I it refers to implementation-supplied functions. Some of these, like SQRT and COSH, are always implemented by calls to library routines; some of them, like LENGTH and SIGN, are always implemented in line; and a very few are implemented sometimes in line and sometimes by a call to a library routine. ABS is the classical example of this mixed case. It is implemented in line, trivially, for real arithmetic values; but for complex ones, for, say,
declare x complex decimal float(15) ; it is implemented by a library call. [The expression abs(a + bi) is defined/evaluated as +sqrt(a**2 + b**2) . Other languages have used different terminologies. In COBOL, for example, implementation-supplied functions/routines are called GENERIC ones. In C they have usually been called [standard] library functions. In PL/I such a declaration as, say, declare sqrt builtin ; followed by x = sqrt(y) ; forces the compiler or interpreter to use the implementation-supplied sqrt routine. If this declaration is omitted an attempt is first made to find and use another sqrt facility, and only if one is not found is the builtin facility used. (The search can be influenced by the presence of a programmer-supplied generic declaration.) Historically, compilers have found it easier to reuse values they generate in line, but they do not always elect to do so for various reasons. Values obtained by function calls can in PL/I and some other languages be characterized explicitly as reducible, in which case multiple subroutine calls or function references to the same exterrnal routine that are identical, specify the same unchanged arguments (actual parameters), can be reduced to a single one. (This can of course be highly problematic; the classic nightmare case is that of reducing calls to a pseudo-random number generator, a sequence-number generator, or the like.) John Gilmore, Ashland, MA 01721 - USA ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
