vise/go/vm/vm.go
2023-04-02 12:12:06 +01:00

187 lines
3.9 KiB
Go

package vm
import (
"encoding/binary"
"fmt"
)
func ParseLoad(b []byte) (string, uint32, []byte, error) {
return parseSymLen(b, LOAD)
}
func ParseReload(b []byte) (string, []byte, error) {
return parseSym(b, RELOAD)
}
func ParseMap(b []byte) (string, []byte, error) {
return parseSym(b, MAP)
}
func ParseMove(b []byte) (string, []byte, error) {
return parseSym(b, MOVE)
}
func ParseHalt(b []byte) ([]byte, error) {
return parseNoArg(b, HALT)
}
func ParseCatch(b []byte) (string, uint8, []byte, error) {
return parseSymSig(b, CATCH)
}
func ParseCroak(b []byte) (string, uint8, []byte, error) {
return parseSymSig(b, CROAK)
}
func ParseInCmp(b []byte) (string, string, []byte, error) {
return parseTwoSym(b, INCMP)
}
func parseNoArg(b []byte, op Opcode) ([]byte, error) {
return opCheck(b, op)
}
func parseSym(b []byte, op Opcode) (string, []byte, error) {
b, err := opCheck(b, op)
if err != nil {
return "", b, err
}
sym, tail, err := instructionSplit(b)
if err != nil {
return "", b, err
}
return sym, tail, nil
}
func parseTwoSym(b []byte, op Opcode) (string, string, []byte, error) {
b, err := opCheck(b, op)
if err != nil {
return "", "", b, err
}
symOne, tail, err := instructionSplit(b)
if err != nil {
return "", "", b, err
}
symTwo, tail, err := instructionSplit(tail)
if err != nil {
return "", "", tail, err
}
return symOne, symTwo, tail, nil
}
func parseSymLen(b []byte, op Opcode) (string, uint32, []byte, error) {
b, err := opCheck(b, op)
if err != nil {
return "", 0, b, err
}
sym, tail, err := instructionSplit(b)
if err != nil {
return "", 0, b, err
}
sz, tail, err := intSplit(tail)
if err != nil {
return "", 0, b, err
}
return sym, sz, tail, nil
}
func parseSymSig(b []byte, op Opcode) (string, uint8, []byte, error) {
b, err := opCheck(b, op)
if err != nil {
return "", 0, b, err
}
sym, tail, err := instructionSplit(b)
if err != nil {
return "", 0, b, err
}
if len(tail) == 0 {
return "", 0, b, fmt.Errorf("instruction too short")
}
n := tail[0]
tail = tail[1:]
return sym, n, tail, nil
}
// NewLine creates a new instruction line for the VM.
func NewLine(instructionList []byte, instruction uint16, strargs []string, byteargs []byte, numargs []uint8) []byte {
if instructionList == nil {
instructionList = []byte{}
}
b := []byte{0x00, 0x00}
binary.BigEndian.PutUint16(b, instruction)
for _, arg := range strargs {
b = append(b, uint8(len(arg)))
b = append(b, []byte(arg)...)
}
if byteargs != nil {
b = append(b, uint8(len(byteargs)))
b = append(b, byteargs...)
}
if numargs != nil {
b = append(b, numargs...)
}
return append(instructionList, b...)
}
func intSplit(b []byte) (uint32, []byte, error) {
l := uint8(b[0])
sz := uint32(l)
b = b[1:]
if l > 0 {
r := []byte{0, 0, 0, 0}
c := 0
ll := 4 - l
var i uint8
for i = 0; i < 4; i++ {
if i >= ll {
r[i] = b[c]
c += 1
}
}
sz = binary.BigEndian.Uint32(r)
b = b[l:]
}
return sz, b, nil
}
// split instruction into symbol and arguments
func instructionSplit(b []byte) (string, []byte, error) {
if len(b) == 0 {
return "", nil, fmt.Errorf("argument is empty")
}
sz := uint8(b[0])
if sz == 0 {
return "", nil, fmt.Errorf("zero-length argument")
}
tailSz := uint8(len(b))
if tailSz < sz {
return "", nil, fmt.Errorf("corrupt instruction, len %v less than symbol length: %v", tailSz, sz)
}
r := string(b[1:1+sz])
return r, b[1+sz:], nil
}
func opCheck(b []byte, opIn Opcode) ([]byte, error) {
op, b, err := opSplit(b)
if err != nil {
return b, err
}
if op != opIn {
return b, fmt.Errorf("not a %v instruction", op)
}
return b, nil
}
func opSplit(b []byte) (Opcode, []byte, error) {
l := len(b)
if l < 2 {
return 0, b, fmt.Errorf("input size %v too short for opcode", l)
}
op := binary.BigEndian.Uint16(b)
if op > _MAX {
return 0, b, fmt.Errorf("invalid opcode %v", op)
}
return Opcode(op), b[2:], nil
}