Return to honorp CVS log

Up to [Research Unix] / researchv10no / cmd / f2c

Annotation of researchv10no/cmd/f2c/honorp, revision 1.1

1.1     ! root        1: From alice!dmr Wed Apr 11 09:08:05 EDT 1990
        !             2: 
        !             3: honorp (dmr) Wed Apr 11 01:46:18 1990
        !             4: 
        !             5:    There is confusion about the rearrangement rules in the K&R 1
        !             6:    language and about how ANSI C changed things.  The wording in K&R 1
        !             7:    wasn't precise enough in any event, but there was also a real
        !             8:    change in content.
        !             9: 
        !            10:    K&R 1 said, "Expressions involving a commutative and associative
        !            11:    operator (*, +, |, ^) may be rearranged arbitrarily, even in
        !            12:    the parentheses; to enforce a particular order of evaluation
        !            13:    an explicit temporary must be used."
        !            14: 
        !            15:    The exact intent of this statement was no more than this:
        !            16:    "A compiler is entitled to regard mathematically commutative
        !            17:    and associative operators as computationally commutative and
        !            18:    associative."
        !            19: 
        !            20:    The imprecision of the original statement caused considerable worry,
        !            21:    which still persists; for example it could be interpreted as saying that
        !            22:           along+ashort+ashort
        !            23:    or even
        !            24:           (along+ashort)+ashort
        !            25:    might add the shorts in short precision before adding the sum to the long.
        !            26:    This wasn't the intent, and I don't think it's the practice.
        !            27: 
        !            28:    X3J11 decided not only to clarify the matter, but also to
        !            29:    strengthen the requirements.  Its rule is that the value
        !            30:    of an expression must be computed as if each subexpression
        !            31:    in the parse (including the effects of parentheses) were computed
        !            32:    as written. The temporal order of side effects remains undefined.
        !            33: 
        !            34: 
        !            35: 

This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.