_tolower and _toupper macros

[Stephen Clamage]

ANSI defines toupper (tolower) such that it returns a lowercase (uppercase)
version of an uppercase (lowercase) argument, and returns all other
characters as-is.  There is no definition of _toupper or _tolower in ANSI C.

The implementation of topper (tolower) must check its parameter to see
what it is before converting.  Sometimes the programmer knows that
such a check is not necessary.  Many C implementations provide the
_toupper and _tolower macros, which are faster, to use in such cases.
Although such macros are not guaranteed to exist on all systems, they
are usually easy enough to write if they are not supplied.
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Steve Clamage, TauMetric Corp, steve at taumet.com