On 2013-10-21 11:06, John Gilmore wrote:
>
> [signum] is available as a BIF called sign in PL/I, where it is [almost
> always]
> implemented in line. An analogous function is available for strings
> in C, where it is implemented as a library subroutine. It has always
> been available in FORTRAN in the form of the much deprecated but in
> fact enormously useful arithmetic-IF statement
>
(They seem to have borrowed the name from FORTRAN.)
One might consider implementing a dyadic signum as:
#define signum2( a, b ) ( ( ( a ) < ( b ) ) - ( ( a ) > ( b ) ) )
... in any language where TRUE==1 and FALSE==0. (Is this the case in
PL/I?)
Beware the shortcut:
#define signum2( a, b ) ( signum( ( b ) - ( a ) ) )
... which misbehaves for extreme values of a and b.
Alas, I know of no C implementation which reports integer overflow
of signed operands, although ANSI tolerates this behavior. I prefer
to be told of such exceptional conditions. (Didn't you say that PL/I
lately robbed programmers of that facility?) I find a few occurrences
of FPE_INTOVF buried in /usr/include.
-- gil
