OpenEuphoria

2. Re: Euphoria RPG

• Posted by Robert Craig <rds at MSN.COM> Jul 30, 1997
• 636 views

Eduardo Uemura Okada asks:
> Are this Machine Code the Assembler language?
> This will be very important.

Machine Code is the actual numbers that are stored
in memory.The Machine (the CPU chip) understands these numbers and
can execute them.

If you look at euphoria\demo\callmach.ex you'll see:

                -- String Copy machine code:
                -- (will move at least one char)
string_copy_code =
      {#50,                            -- push eax
       #53,                            -- push ebx
       #52,                            -- push edx
       #B8} &                          -- mov eax,
       int_to_bytes(string_space) &    -- string address (source)
      {#BA} &                          -- mov edx,
       int_to_bytes(screen_location) & -- screen address (destination)
      {#8A, #18,                       -- L1: mov bl, [eax]
       #40,                            -- inc eax
       #88, #1A,                       -- mov [edx],bl
       #83, #C2, #01,                  -- add edx, #1
       #80, #38, #00,                  -- cmp byte ptr [eax], #00
       #75, #F3,                       -- jne L1
       #5A,                            -- pop edx
       #5B,                            -- pop ebx
       #58,                            -- pop eax
       #C3}                            -- ret

-- poke in the machine code:
code_space = allocate(length(string_copy_code))
poke(code_space, string_copy_code)

-- poke in the string:
poke(string_space, string & 0)

puts(1, "\n  calling machine code routine ... ")

-- call the machine code:
call(code_space) -- copies string to screen

-------------------

The numbers that start with # are the bytes
of "machine code". They are shown in hex form because
that's the way they are listed in any book
on machine code.

The first byte is #50, and to the right
I've got a comment that says:

     push eax

and to the right of the other hex numbers I have comments
as well. In these comments I show the "assembly language"
statement that corresponds to the machine code number or numbers.
These comments are not necessary. But without them I would
quickly forget what the hex numbers mean.

In the early days (1940's and 50's),
you had to program a computer by entering this
machine code. In other words, you had to look up
hex codes in a book and load them into the
computer's memory.

Eventually people got tired of looking up codes
in a book, and someone invented a program called
an "assembler", and made up a simple language
called "assembly language". It's easier
for people to remember the "push eax" assembly
language statement than to remember the #50
machine instruction.
By the way, "push eax" means: push the contents of the
32-bit EAX register located on the CPU chip, into a
special place in memory called the "stack".

While assembly language is easier than
machine language, it is much harder than
programming in Euphoria or another "high-level"
language. If you make the slightest mistake
you will likely crash your program or your
whole system, and no one will tell you what
went wrong.

Euphoria lets you add machine code to your
program, but you have to look up the hex
codes yourself just like in the 1940's and 50's.
There is no built-in assembler program inside Euphoria.
On the Euphoria Archive page someone started to
make an assembler for use with Euphoria, but I
don't think it's well debugged yet.

I have a book called
"Intel Microprocessor Programmer's Reference Manual"
that lists all the possible machine instructions
of the 386/486/Pentium CPU's and gives me both the
assembly language statement and the machine code number.

In making up this String Copy example I could have
used the Intel book, but actually I cheated and used
my WATCOM 32-bit C compiler to generate an "assembly
language plus machine code" listing of a string copy
routine that I wrote in C.

Most people can use Euphoria without having to
know anything about machine language, but there are
a few things that you can do in machine language much faster
than in Euphoria.

Regards,
  Rob Craig
  Rapid Deployment Software