Re^2: Parsing through instructions

[DaveMonk]

Ok so this is part of what I have:

 byte 1               byte 2 (optional)
 bits      [ 7 6 5 4 3 2 1 0 ]  [ 7 6 5 4 3 2 1 0 ]
 opcode      - - -             
 mod               -           
 operand1            - - - -
 operand2                         - - - - - - - -

And instructions:

 opcode | instruction | operands (mod 0) | operands (mod 1)
 -------+-------------+------------------+-----------------
 0x00   | jmp         | r1               | r2:r1
 0x01   | movr        | r1, r2           | rx,   imm 
 0x02   | movm        | r1, [ds:r2]      | [ds:r1], r2
 0x03   | add         | r1, r2           | r1,   imm

 flags
 
 cmp r1, r2 instruction results in:
    r1 == r2 => fl = 0
    r1 < r2  => fl = 0xff
    r1 > r2  => fl = 1
 
    jmpe r1
    => if (fl == 0) jmp r1
    else nop

I am then given:

 0x00 0x00 0x00 0x01 0x03 0x02 0x03 0x02 0x03 0x02

But pretty much like you said, I am in need of simulating a processor with given instructions.

[GrandFather]

So the key information you need is that you need to use the bit operators to manipulate the bits in each byte to extract the interesting bit fields. In particular use & (bitwise and) and a bit mask to isolate bit fields, and use the bitwise shift operators >> and << to move fields of bits about. For example, to isolate the op code you'd do something like:

use strict;
use warnings;

my $byte = 0b00100100;
my $opCode = ($byte & 0b11100000) >> 5;

printf "Opcode is 0x%02X\n", $opCode;

Prints:

Opcode is 0x01

See perlop for details about the various Perl operators.

[DaveMonk]

Awesome man, but I still need some help figuring out how to do this for the other 8 instructions, and then run it (the asm code) and dump to a file. But I have been playing around with perlop :)

[GrandFather]

There is nothing more I can tell you that wouldn't amount to writing the code for you. If you can't take it from here then you have been set a task that you are not currently equipped to handle. The rest of the problem is really just applying the mask and shift I've already demonstrated to get at the individual op code fields, and then process the data.

I suggest you play for a while and generate some code of your own. If you are still struggling show us what you have written along with your input data (the sample data you showed already is very unlikely to be real) and the expected output, then describe how it doesn't work for you.