C optimizer

[Peter da Silva]

In article <36034 at bbn.COM>, mesard at bbn.com (Wayne Mesard) writes:
>   A function which is entirely composed of known "pure" operations*
>   is, itself, pure.

> * Where pure operations is defined as functions that produce no side
> effects and return deterministic values, and most operators (excluding
> assignment to dereferenced pointers and globals).

Sounds good.

> Hint: Sleep(3) would,
> I believe, be labelled "pure" under this definition, so something's
> still missing.

No, since I don't think *any* system call is definable as a pure function.
In this case alarm() returns a nondeterministic value *and* produces the
side effect of setting a timer in your process table entry.

Can anyone think of any pure system calls? ioctl(fd, TCGETA, tbuf)?
No, I think a system call should be considered not only a global ref
but a volatile one!
-- 
Peter da Silva, Xenix Support, Ferranti International Controls Corporation.
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