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int86
=====

Syntax
------

     #include <dos.h>
     
     int int86(int ivec, union REGS *in, union REGS *out);

Description
-----------

Note: The `.x.' branch is a problem generator.  Most code expects the
`.x.' branch to have e.g. "`.x.ax'" members, and that they are 16-bit.
If you know you want 32-bit values, use the `.d.eax' members.  If you
know you want 16-bit values, use the `.w.ax' members.  The `.x.'
members behave according to `#defines', as follows:

`default'
     If you specify no `#define', the `.x.' branch has "`ax'" members
     and is 32-bit.  This is compatible with previous versions of djgpp.

`_NAIVE_DOS_REGS'
     This define gives you `.x.ax', but they are 16-bit.  This is
     probably what most programs ported from 16-bit dos compilers will
     want.

`_BORLAND_DOS_REGS'
     This define gives you `.x.eax' which are 32-bit.  This is
     compatible with Borland's 32-bit compilers.

This function simulates a software interrupt.  Note that, unlike the
`__dpmi_int' function, requests that go through `int86' and similar
functions are specially processed to make them suitable for invoking
real-mode interrupts from protected-mode programs.  For example, if a
particular routine takes a pointer in `BX', `int86' expects you to put
a (protected-mode) pointer in `EBX'.  Therefore, `int86' should have
specific support for every interrupt and function you invoke this way.
Currently, it supports only a subset of all available interrupts and
functions:

1) All functions of any interrupt which expects only scalar arguments
registers (i.e., no pointers to buffers).

2) In addition, the following functions of interrupt 21h are supported:
9, 39h, 3Ah, 3Bh, 3Ch, 3Dh, 3Fh, 40h, 41h, 43h, 47h, 56h.

When the interrupt is invoked, the CPU registers are copied from IN.
After the interrupt, the CPU registers are copied to OUT.

This function is just like `int86x' (int86x:.) except that   
suitable default values are used for the segment registers.

int86x:. intdos:. bdos:.         

Return Value
------------

The returned value of `EAX'.

Example
-------

     union REGS r;
     r.x.ax = 0x0100;
     r.h.dl = 'c';
     int86(0x21, &r, &r);