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package j1
import (
"bytes"
"encoding/binary"
"fmt"
"io/ioutil"
"time"
)
// J1 Forth processor VM
type J1 struct {
pc uint16 // 13 bit
st0 uint16 // top of data stack
dsp int8 // 5 bit data stack pointer
rsp int8 // 5 bit retrun stack pointer
dstack [0x20]uint16 // data stack
rstack [0x20]uint16 // return stack
memory [0x8000]uint16 // 0..0x3fff main memory, 0x4000 .. 0x7fff mem-mapped i/o
}
// Reset VM
func (j1 *J1) Reset() {
j1.pc = 0
j1.st0 = 0
j1.dsp = 0
j1.rsp = 0
}
// LoadBytes into memory
func (j1 *J1) LoadBytes(data []byte) error {
size := len(data) >> 1
if size > len(j1.memory) {
return fmt.Errorf("too big")
}
return binary.Read(bytes.NewReader(data), binary.BigEndian, j1.memory[:size])
}
// LoadFile into memory
func (j1 *J1) LoadFile(fname string) error {
data, err := ioutil.ReadFile(fname)
if err != nil {
return err
}
return j1.LoadBytes(data)
}
// Eval evaluates content of memory
func (j1 *J1) Eval() {
var cycle int
ticker := time.NewTicker(time.Second / 10)
defer ticker.Stop()
for range ticker.C {
cycle++
ins := Decode(j1.memory[j1.pc])
if ins == Jump(0) {
return
}
j1.eval(ins)
fmt.Printf("%4d %v\n", cycle, ins)
fmt.Printf("%v\n", j1)
}
}
func (j1 *J1) String() string {
var rstack [32]uint16
for i, v := range j1.rstack {
rstack[i] = v << 1
}
s := fmt.Sprintf("\tPC=%0.4X ST=%0.4X\n", j1.pc<<1, j1.st0)
s += fmt.Sprintf("\tD=%0.4X\n", j1.dstack[:j1.dsp+1])
s += fmt.Sprintf("\tR=%0.4X\n", rstack[:j1.rsp+1])
return s
}
func (j1 *J1) eval(ins Instruction) {
switch v := ins.(type) {
case Lit:
j1.pc++
j1.dsp++
j1.dstack[j1.dsp] = j1.st0
j1.st0 = v.Value()
case Jump:
j1.pc = v.Value()
case Call:
j1.rsp++
j1.rstack[j1.rsp] = j1.pc + 1
j1.pc = v.Value()
case Cond:
j1.pc++
if j1.st0 == 0 {
j1.pc = v.Value()
}
j1.st0 = j1.dstack[j1.dsp] // N
j1.dsp--
case ALU:
st0 := j1.newST0(v.Opcode)
j1.pc++
if v.RtoPC {
j1.pc = j1.rstack[j1.rsp]
}
if v.NtoAtT {
j1.memory[j1.st0] = j1.dstack[j1.dsp]
}
j1.dsp += v.Ddir
j1.rsp += v.Rdir
if v.TtoR {
j1.rstack[j1.rsp] = j1.st0
}
if v.TtoN {
j1.dstack[j1.dsp] = j1.st0
}
j1.st0 = st0
}
}
func (j1 *J1) newST0(opcode uint16) uint16 {
T, N, R := j1.st0, j1.dstack[j1.dsp], j1.rstack[j1.rsp]
switch opcode {
case opT: // T
return T
case opN: // N
return N
case opTplusN: // T+N
return T + N
case opTandN: // T&N
return T & N
case opTorN: // T|N
return T | N
case opTxorN: // T^N
return T ^ N
case opNotT: // ~T
return ^T
case opNeqT: // N==T
if N == T {
return 1
}
return 0
case opNleT: // N<T
if int16(N) < int16(T) {
return 1
}
return 0
case opNrshiftT: // N>>T
return N >> (T & 0xf)
case opTminus1: // T-1
return T - 1
case opR: // R (rT)
return R
case opAtT: // [T]
return j1.memory[T]
case opNlshiftT: // N<<T
return N << (T & 0xf)
case opDepth: // depth (dsp)
return (uint16(j1.rsp) << 8) | uint16(j1.dsp)
case opNuleT: // Nu<T
if N < T {
return 1
}
return 0
default:
panic("invalid instruction")
}
}
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