table of functions vs switch in golang

Question

im am writing a simple emulator in go (should i? or should i go back to c?). anyway, i am fetching the instruction and decoding it. at this point i have a byte like 0x81, and i have to execute the right function.

should i have something like this

func (sys *cpu) eval() {
    switch opcode {
    case 0x80:
        sys.add(sys.b)
    case 0x81:
        sys.add(sys.c)
    etc
    }
}

or something like this

var fnTable = []func(*cpu) {
    0x80: func(sys *cpu) {
        sys.add(sys.b)
    },
    0x81: func(sys *cpu) {
        sys.add(sys.c)
    }
}
func (sys *cpu) eval() {
    return fnTable[opcode](sys)
}

1.which one is better?
2.which one is faster?
also
3.can i declare a function inline?
4.i have a cpu struct in which i have the registers etc. would it be faster if i have the registers and all as globals? (without the struct)

thank you very much.

Answer 1

I did some benchmarks and the table version is faster than the switch version once you have more than about 4 cases.

I was surprised to discover that the Go compiler (gc, anyway; not sure about gccgo) doesn't seem to be smart enough to turn a dense switch into a jump table.

Update: Ken Thompson posted on the Go mailing list describing the difficulties of optimizing switch.