Borland Turbo C 2.0 for Atari 68000 machines: ODD behavior

[Checkpoint Technologies]

In article <1991Apr6.091013.26131 at daffy.cs.wisc.edu> carter at cs.wisc.edu (Gregory Carter) writes:
> (unsigned int)(*((unsigned int *)0x00ff8e20L)) = 0x03;
>                       MOVE.W #$0003, $00ff8e20
>...
> (unsigned int)(*((unsigned int *)0xffff8e20L)) = 0x03;
>                       MOVE.W #$0003, $8e20
>
>This is obviously not correct.

This may not be obvious, but it *is* correct.  The compiler is doing you a
favor.

The 68K has "absolute short" and "absolute long" addressing.  Absolute
long means that a whole 32 bit absoluet address follows.

Absolute short means that only a 16 bit word follows, and it should be
*sign extended* to 32 bits before being used.

The value $8E20, when sign extended into a full 32 bit address becomes
$FFFF8E20.  This is just what you asked for, and the compiler found a
briefer way to code it.
-- 
ckp at grebyn.com
[brychcy at informatik.tu-muenchen.dbp.de (Till Brychcy) also pointed this out.
-John]
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