Antti Lukats <PICLIST@MITVMA.MIT.EDU> wrote:

> apparently there is a bug with >> more than 15 bits see code
> snipped below, both #define are identical, but only one works.
>
>
>                     00004 #define BYTE_2(a) (a >> 16) & 0xFF
>                     00005 #define BYTE_2x(a) (a >> 8 >> 8) & 0xFF
>                     00006
>   12345678          00007 mylong_thing = 0x12345678
>                     00008
>
> 0000 3048           00009  movlw BYTE_2(mylong_thing)
> ;      ^ this one messes up MPASM 1.40 bug???
>
> 0001 3034           00010  movlw BYTE_2x(mylong_thing)
> ;      ^ this one works fine

    You're going to laugh, Antti... Kim Cooper and I certainly did
    when we figured out what was happening.

    Here... I'll walk you through it:

        0x12345678, expressed in binary, is:

            00010010001101000101011001111000

        The result you got was 0x48.  Expressed in binary, 0x48 is:

            01001000

        Ok... Where in the original number does that bit-pattern
        appear?

        If you look closely, you'll see that it appears in bit
        positions 22 through 29... It seems that your "a >> 16"
        expression was actually working like "a >> 22", right?

    At this point, the answer should be dawning, but just in case it
    isn't...

        Decimal 22 = Hexadecimal 16.

        Oops.

    Change your #defines to read ".... a >> 0x10", or add a "LIST
    R=DEC" directive at the start of your program, and everything
    will work fine.

    -Andy

=== Andrew Warren - fastfwd@ix.netcom.com
=== Fast Forward Engineering - Vista, California
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