From: Gregory Millam <walker@...>
Date: 2004-04-03T09:51:44+09:00
Subject: Re: Learning Ruby, was a C geek...

Received: Sat, 3 Apr 2004 08:37:54 +0900
And lo, Nicholas wrote:

> I've written it, and it works correctly when compared to my program 
> written in C, but at its core is a large case-when-end statement.  
> This is not `sexy.'  I was wondering if there was a better way to do 
> this in Ruby, or if I'm just missing the point.

This is a project similar in scope to an NES emulator I've written in C. When doing so, I tried and benchmarked 2 situations:

switch (opcode) {
 case 0x01:
 case 0x02 ... (etc, for every opcode)
}

And:
typedef void (*operand)(address);
operand opcodes[0x100]; (You'd use 0x10)
op_0x01(int address) { ... }
opcodes[0x01] = op_0x01.
Then call using: opcodes[0x01](addr);

Ruby caters to the second style rather well, adding in lambda blocks.

ops = []
ops[0x01] = lambda { /* incrememnt accum 1 */ |address| Cpu.accum += 1 }

Either a hash or an array could do the job. 

You'd really just need to fetch op[instruction byte 1 >> 4], if I'm reading that specs document correctly.

Hope that helps

- Greg Millam