Re: HEAD: inclusion order wrong for input.c

[Eric Blake]

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According to Gary V. Vaughan on 4/2/2007 4:37 PM:
>> Cast the subscript to unsigned char before using it as index.
>> Otherwise, on a system where char is signed, and its high bit is set,
>> and you haven't adjusted the array range to allow for negative values,
>> fun will ensue.
> 
> If the table value for META-^A is held at element 128 of the array (since
> the table was built assuming char* is unsigned by default), and we compile
> on a host with signed chars, does the signed char value of META-^A still
> become 128 when cast to unsigned char?  Or does 2's complement come into
> play and scramble the order of the negative signed char values when
> casting them before doing a table lookup?

As long as the table is handled consistently (in other words, as long as
ALL uses of characters as indices occur as unsigned char or within
to_uchar), then META-^A (usually encoded as -128 in signed char) will
always appear at the same index, regardless of whether that index is 128
(as it will be on 2's complement machine; the bulk of what exists today),
or 255 (which is what (unsigned char) -128 might become on a 1's
compliment machine, mostly theoretical).  You only run into the bug that
you were describing if you also reference the array based on a given
integer encoding of characters.

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
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