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package j1
import (
"bytes"
"encoding/binary"
"errors"
"fmt"
"io/ioutil"
)
var ErrStop = errors.New("stop")
// Console i/o
type Console interface {
Read() uint16
Write(uint16)
Len() uint16
}
// Core of J1 Forth CPU
//
// memory: 0x2000 words (16k) addressed by byte
type Core struct {
memory [0x2000]uint16 // 0..0x3fff main memory, 0x4000 .. 0xffff mem-mapped i/o
pc uint16 // 13 bit
st0 uint16 // top of data stack
d, r stack // data and return stacks
console Console // console i/o
}
// New core with console i/o
func New(con Console) *Core {
return &Core{console: con}
}
// Reset VM
func (c *Core) Reset() {
c.pc, c.st0, c.d.sp, c.r.sp = 0, 0, 0, 0
}
// LoadBytes into memory
func (c *Core) LoadBytes(data []byte) error {
size := len(data) >> 1
if size >= len(c.memory) {
return errors.New("too big")
}
return binary.Read(bytes.NewReader(data), binary.LittleEndian, c.memory[:size])
}
// LoadFile into memory
func (c *Core) LoadFile(fname string) error {
data, err := ioutil.ReadFile(fname)
if err != nil {
return err
}
return c.LoadBytes(data)
}
func (c *Core) String() string {
s := fmt.Sprintf("\tPC=%0.4X ST=%0.4X\n", c.pc, c.st0)
s += fmt.Sprintf("\tD=%0.4X\n", c.d.dump())
s += fmt.Sprintf("\tR=%0.4X\n", c.r.dump())
return s
}
const ioMask = 3 << 14
func (c *Core) writeAt(addr, value uint16) error {
if addr&ioMask == 0 {
c.memory[addr>>1] = value
}
switch addr {
case 0x7000: // key
c.console.Write(value)
case 0x7002: // bye
return ErrStop
}
return nil
}
func (c *Core) readAt(addr uint16) uint16 {
if addr&ioMask == 0 {
return c.memory[addr>>1]
}
switch addr {
case 0x7000: // tx!
return c.console.Read()
case 0x7001: // ?rx
return c.console.Len()
}
return 0
}
// Run evaluates content of memory
func (c *Core) Run() {
for {
ins := c.Decode()
err := c.Eval(ins)
if err == ErrStop {
return
}
}
}
// Decode instruction
func (c *Core) Decode() Instruction {
return Decode(c.memory[c.pc])
}
// Eval instruction
func (c *Core) Eval(ins Instruction) error {
c.pc++
switch v := ins.(type) {
case Literal:
c.d.push(c.st0)
c.st0 = v.value()
case Jump:
c.pc = v.value()
case Call:
c.r.push(c.pc << 1)
c.pc = v.value()
case Conditional:
if c.st0 == 0 {
c.pc = v.value()
}
c.st0 = c.d.pop()
case ALU:
if v.RtoPC {
c.pc = c.r.peek() >> 1
}
if v.NtoAtT {
err := c.writeAt(c.st0, c.d.peek())
if err != nil {
return err
}
}
st0 := c.newST0(v.Opcode)
c.d.move(v.Ddir)
c.r.move(v.Rdir)
if v.TtoN {
c.d.replace(c.st0)
}
if v.TtoR {
c.r.replace(c.st0)
}
c.st0 = st0
}
return nil
}
var boolValue = map[bool]uint16{
false: 0,
true: ^uint16(0),
}
func (c *Core) newST0(opcode uint16) uint16 {
T, N, R := c.st0, c.d.peek(), c.r.peek()
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
return boolValue[N == T]
case opNleT: // N<T
return boolValue[int16(N) < int16(T)]
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 c.readAt(T)
case opNlshiftT: // N<<T
return N << (T & 0xf)
case opDepth: // depth (dsp)
return (c.r.depth() << 8) | c.d.depth()
case opNuleT: // Nu<T
return boolValue[N < T]
default:
panic("invalid instruction")
}
}
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