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package vm1
import (
"fmt" // for tracing only
"reflect" // for optional CallX only
"strconv" // for tracing only
)
const debug = true
// Byte-code instruction set.
const (
// instruction effect on stack: values consumed -- values produced
Nop = iota // --
Add // n1 n2 -- sum ; sum = n1+n2
Assign // val -- ; mem[$1] = val
Call // f [a1 .. ai] -- [r1 .. rj] ; r1, ... = prog[f](a1, ...)
CallX // f [a1 .. ai] -- [r1 .. rj] ; r1, ... = mem[f](a1, ...)
Dup // addr -- value ; value = mem[addr]
Fdup // addr -- value ; value = mem[addr]
Exit // -- ;
Jump // -- ; ip += $1
JumpTrue // cond -- ; if cond { ip += $1 }
JumpFalse // cond -- ; if cond { ip += $1 }
Lower // n1 n2 -- cond ; cond = n1 < n2
Loweri // n1 -- cond ; cond = n1 < $1
Pop // v --
Push // -- v
Return // [r1 .. ri] -- ; exit frame: sp = fp, fp = pop
Sub // n1 n2 -- diff ; diff = n1 - n2
Subi // n1 -- diff ; diff = n1 - $1
)
var strop = [...]string{ // for VM tracing.
Nop: "Nop",
Add: "Add",
Assign: "Assign",
Call: "Call",
CallX: "CallX",
Dup: "Dup",
Fdup: "Fdup",
Exit: "Exit",
Jump: "Jump",
JumpTrue: "JumpTrue",
JumpFalse: "JumpFalse",
Lower: "Lower",
Loweri: "Loweri",
Pop: "Pop",
Push: "Push",
Return: "Return",
Sub: "Sub",
Subi: "Subi",
}
// Machine represents a virtual machine.
type Machine struct {
code [][]int64 // code to execute
mem []any // memory, as a stack
ip, fp int // instruction and frame pointer
// flags uint // to set options such as restrict CallX, etc...
}
// Run runs a program.
func (m *Machine) Run() (err error) {
code, mem, ip, fp, sp := m.code, m.mem, m.ip, m.fp, 0
defer func() { m.mem, m.ip, m.fp = mem, ip, fp }()
trace := func() {
if !debug {
return
}
var op2, op3 string
c := code[ip]
if l := len(c); l > 2 {
op2 = strconv.Itoa(int(c[2]))
if l > 3 {
op3 = strconv.Itoa(int(c[3]))
}
}
fmt.Printf("ip:%-4d sp:%-4d fp:%-4d op:[%-9s %-4s %-4s] mem:%v\n", ip, sp, fp, strop[c[1]], op2, op3, mem)
}
for {
sp = len(mem) // stack pointer
trace()
switch op := code[ip]; op[1] {
case Add:
mem[sp-2] = mem[sp-2].(int) + mem[sp-1].(int)
mem = mem[:sp-1]
case Assign:
mem[op[2]] = mem[sp-1]
mem = mem[:sp-1]
case Call:
mem = append(mem, ip+1, fp)
fp = sp + 2
ip += int(op[2])
continue
case CallX: // Should be made optional.
l := int(op[2])
in := make([]reflect.Value, l)
for i := range in {
in[l-1-i] = reflect.ValueOf(mem[sp-1-i])
}
f := reflect.ValueOf(mem[sp-l-1])
mem = mem[:sp-l-1]
for _, v := range f.Call(in) {
mem = append(mem, v.Interface())
}
case Dup:
mem = append(mem, mem[int(op[2])])
case Exit:
return
case Fdup:
mem = append(mem, mem[int(op[2])+fp-1])
case Jump:
ip += int(op[2])
continue
case JumpTrue:
cond := mem[sp-1].(bool)
mem = mem[:sp-1]
if cond {
ip += int(op[2])
continue
}
case JumpFalse:
cond := mem[sp-1].(bool)
mem = mem[:sp-1]
if !cond {
ip += int(op[2])
continue
}
case Lower:
mem[sp-2] = mem[sp-2].(int) < mem[sp-1].(int)
mem = mem[:sp-1]
case Loweri:
mem[sp-1] = mem[sp-1].(int) < int(op[2])
case Pop:
mem = mem[:sp-1]
case Push:
mem = append(mem, int(op[2]))
case Return:
ip = mem[fp-2].(int)
ofp := fp
fp = mem[fp-1].(int)
mem = append(mem[:ofp-int(op[2])-int(op[3])-1], mem[sp-int(op[2]):]...)
continue
case Sub:
mem[sp-2] = mem[sp-2].(int) - mem[sp-1].(int)
mem = mem[:sp-1]
case Subi:
mem[sp-1] = mem[sp-1].(int) - int(op[2])
}
ip++
}
}
func (m *Machine) PushCode(code ...[]int64) (p int) {
p = len(m.code)
m.code = append(m.code, code...)
return p
}
func (m *Machine) SetIP(ip int) { m.ip = ip }
func (m *Machine) Push(v ...any) (l int) { l = len(m.mem); m.mem = append(m.mem, v...); return }
func (m *Machine) Pop() (v any) { l := len(m.mem) - 1; v = m.mem[l]; m.mem = m.mem[:l]; return }
func (m *Machine) PopExit() {
if l := len(m.code); l > 0 && m.code[l-1][1] == Exit {
m.code = m.code[:l-1]
}
}
// Disassemble returns the code as a readable string.
func Disassemble(code [][]int64) (asm string) {
for _, op := range code {
switch len(op) {
case 2:
asm += strop[op[1]] + "\n"
case 3:
asm += fmt.Sprintf("%s %d\n", strop[op[1]], op[2])
case 4:
asm += fmt.Sprintf("%s %d %d\n", strop[op[1]], op[2], op[3])
}
}
return asm
}
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