aboutsummaryrefslogtreecommitdiff
path: root/eval.go
blob: da962f55f1adf7ee71e8c40a885ba0b521fd5ddb (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
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   // deturn stack
	memory [0x8000]uint16 // memory
}

// Reset VM
func (vm *J1) Reset() {
	vm.pc = 0
	vm.st0 = 0
	vm.dsp = 0
	vm.rsp = 0
}

// Depth of stacks
func (vm *J1) Depth() uint16 { return (uint16(vm.rsp) << 8) | uint16(vm.dsp) }

// T is top of the data stack
func (vm *J1) T() uint16 { return vm.st0 }

// N is sendond element in data stack
func (vm *J1) N() uint16 { return vm.dstack[vm.dsp] }

// R is top of return stack
func (vm *J1) R() uint16 { return vm.rstack[vm.rsp] }

// LoadBytes into memory
func (vm *J1) LoadBytes(data []byte) error {
	size := len(data) >> 1
	if size > len(vm.memory) {
		return fmt.Errorf("too big")
	}
	return binary.Read(bytes.NewReader(data), binary.BigEndian, vm.memory[:size])
}

// LoadFile into memory
func (vm *J1) LoadFile(fname string) error {
	data, err := ioutil.ReadFile(fname)
	if err != nil {
		return err
	}
	return vm.LoadBytes(data)
}

// Eval evaluates content of memory
func (vm *J1) Eval() {
	var cycle int
	ticker := time.NewTicker(time.Second / 10)
	defer ticker.Stop()
	for range ticker.C {
		cycle++
		ins := Decode(vm.memory[vm.pc])
		if ins == Jump(0) {
			return
		}
		vm.eval(ins)
		fmt.Printf("%4d %v\n", cycle, ins)
		fmt.Printf("%v\n", vm)
	}
}

func (vm *J1) String() string {
	var rstack [32]uint16
	for i, v := range vm.rstack {
		rstack[i] = v << 1
	}
	s := fmt.Sprintf("\tPC=%0.4X ST=%0.4X\n", vm.pc<<1, vm.st0)
	s += fmt.Sprintf("\tD=%0.4X\n", vm.dstack[:vm.dsp+1])
	s += fmt.Sprintf("\tR=%0.4X\n", rstack[:vm.rsp+1])
	return s
}

func (vm *J1) eval(ins Instruction) {
	switch v := ins.(type) {
	case Lit:
		vm.pc++
		vm.dsp++
		vm.dstack[vm.dsp] = vm.st0
		vm.st0 = v.Value()
	case Jump:
		vm.pc = v.Value()
	case Call:
		vm.rsp++
		vm.rstack[vm.rsp] = vm.pc + 1
		vm.pc = v.Value()
	case Cond:
		vm.pc++
		if vm.st0 == 0 {
			vm.pc = v.Value()
		}
		vm.st0 = vm.dstack[vm.dsp] // N
		vm.dsp--
	case ALU:
		st0 := vm.newST0(v)
		vm.pc++
		if v.RtoPC {
			vm.pc = vm.rstack[vm.rsp]
		}
		if v.NtoAtT {
			vm.memory[vm.st0] = vm.dstack[vm.dsp]
		}
		vm.dsp += v.Ddir
		vm.rsp += v.Rdir
		if v.TtoR {
			vm.rstack[vm.rsp] = vm.st0
		}
		if v.TtoN {
			vm.dstack[vm.dsp] = vm.st0
		}
		vm.st0 = st0
	}
}

func (vm *J1) newST0(v ALU) uint16 {
	switch v.Opcode {
	case opT: // T
		return vm.T()
	case opN: // N
		return vm.N()
	case opTplusN: // T+N
		return vm.T() + vm.N()
	case opTandN: // T&N
		return vm.T() & vm.N()
	case opTorN: // T|N
		return vm.T() | vm.N()
	case opTxorN: // T^N
		return vm.T() ^ vm.N()
	case opNotT: // ~T
		return ^vm.T()
	case opNeqT: // N==T
		if vm.N() == vm.T() {
			return 1
		}
		return 0
	case opNleT: // N<T
		if int16(vm.N()) < int16(vm.T()) {
			return 1
		}
		return 0
	case opNrshiftT: // N>>T
		return vm.N() >> (vm.T() & 0xf)
	case opTminus1: // T-1
		return vm.T() - 1
	case opR: // R (rT)
		return vm.R()
	case opAtT: // [T]
		return vm.memory[vm.T()]
	case opNlshiftT: // N<<T
		return vm.N() << (vm.T() & 0xf)
	case opDepth: // depth (dsp)
		return vm.Depth()
	case opNuleT: // Nu<T
		if vm.N() < vm.T() {
			return 1
		}
		return 0
	default:
		panic("invalid instruction")
	}
}