On Tue, 10 Jun 1997 07:52:35 -0700 Scott Dattalo <sdattalo@unix.SRI.COM>
writes:
>Dwayne Reid wrote:
>> I posted a set of routines to the list back in March: HEXASCII (hex
>to
>> Ascii), ASCIIHEX (ascii to hex) and UPCASE.  I dug them out when I
>read
>> Eric's challange and like Scott, I'll repost my version of toascii
>without
>> comments.
>
><snip>
>>     skpndc
>
>  Oh yeah! The 'used-once-in-a-blue-moon-digit-carry'.

If the ASCII code for 'A' were 0x40 rather than 0x41, then the DC could
be used to write a 3 instruction (plus return) toascii.  But it isn't,
and using DC has no advantage over the 8th-bit Carry.


>BTW. Does anyone have a good explanation why
>        ADDLW   -('z'+1)     ==> -('z'+1) evaluates correctly to 0x85
>assembles differently than
>        ADDLW   -'z'-1       ==> -'z'-1 evaluates incorrectly to 0x87
>
>(I'm using the pre-historic version 3.12.00 of MPLAB)

A couple of clues: Ver. 3.22.00 does the same thing, but
        ADDLW   0-'z'-1
will evaluate to 0x85.  My "good explanation" is that the - sign with
nothing on the left is negation, and it (at least unconventionally, if
not mistakenly) has lower priority than subtraction.  Writing the
negation as a subtraction from zero increases the priority so the
expression evaluates from left to right as expected.

-'z'-1 -->  -('z'-1), not -('z') + -(1)
0-'z'-1 --> (0-'z')-1

Some of the early MPALCs did really strange things with compile-time
expressions.  They are getting better...