-=> On 28 Jun 96  19:39:04 <=-
-=> Frank Adam was heard to tell All <=-

    Hi Frank,

 FA> Just curious why is REGS a union and not a struct ? It feels like
 FA> one..

    Because the registers come in a variety of sizes REGS has to be
a union.  Al & AH are byte wide (CHAR) while AX is the same two but
joined at the hips, therefore it's a word (INT).  For those with
something a little more than advanced than my XT there is also a 32
bit version (EAX?).  When I was trying to get the hang of this
structure/union thing I found that it all made sense once I saw it
applied to the registers.  Probably a side effect of having been
using assembler for so long.

 FA> And can anyone show or guide me to a C snippet,on how to retrieve the
 FA> adress of DTA(Disk Transfer Adress) ?
 FA> The following should work ( i thought ), but it just boots.
 FA> Perhaps the bit between the braces is wrong ? :o)

 FA> char* Get_DTA()
 FA> {
 FA> char far* ptr;
 FA> union REGS regs;
 FA> struct SREGS sregs;
 FA>
 FA> regs.x.ax = 0x2f00;
 FA> int86x(0x21,®s,®s,&sregs);
 FA> ptr = (char far*) MK_FP((unsigned)sregs.es,(usigned)regs.x.dx);
 FA> };

    The error is in using ES:DX, it should be ES:BX.  I just have to
ask, why do you (or anyone else) use such long winded code?
Whenever I need to do anything at the register level I simply use
in-line assembler code.  This is even more important if you are
after any kind of speed.  For me one of the most powerful features
of C is the ability to easily create hybrid programs, where you have
the convenience of a high level language for easy coding and the
speed of assembler where it's needed.

            John

... When the snow melts, where does all the white go?
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