Update compiler (#22)

* refactor to use ast.Walk for recursive converting
* added lots of test cases
* added a new way to handle jump labels
* function calls with multiple arguments
* binary expression (LOR LAND)
* struct types + method receives
* cleaner opcode dumps, side by side diff for debugging test cases

pkg/vm/compiler/emit.go

@@ -0,0 +1,101 @@
+package compiler
+
+import (
+	"bytes"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"math/big"
+
+	"github.com/CityOfZion/neo-go/pkg/util"
+	"github.com/CityOfZion/neo-go/pkg/vm"
+)
+
+func emit(w *bytes.Buffer, op vm.Opcode, b []byte) error {
+	if err := w.WriteByte(byte(op)); err != nil {
+		return err
+	}
+	_, err := w.Write(b)
+	return err
+}
+
+func emitOpcode(w *bytes.Buffer, op vm.Opcode) error {
+	return w.WriteByte(byte(op))
+}
+
+func emitBool(w *bytes.Buffer, ok bool) error {
+	if ok {
+		return emitOpcode(w, vm.Opusht)
+	}
+	return emitOpcode(w, vm.Opushf)
+}
+
+func emitInt(w *bytes.Buffer, i int64) error {
+	if i == -1 {
+		return emitOpcode(w, vm.Opushm1)
+	}
+	if i == 0 {
+		return emitOpcode(w, vm.Opushf)
+	}
+	if i > 0 && i < 16 {
+		val := vm.Opcode((int(vm.Opush1) - 1 + int(i)))
+		return emitOpcode(w, val)
+	}
+
+	bInt := big.NewInt(i)
+	val := util.ToArrayReverse(bInt.Bytes())
+	return emitBytes(w, val)
+}
+
+func emitString(w *bytes.Buffer, s string) error {
+	return emitBytes(w, []byte(s))
+}
+
+func emitBytes(w *bytes.Buffer, b []byte) error {
+	var (
+		err error
+		n   = len(b)
+	)
+
+	if n == 0 {
+		return errors.New("cannot emit 0 bytes")
+	}
+	if n <= int(vm.Opushbytes75) {
+		return emit(w, vm.Opcode(n), b)
+	} else if n < 0x100 {
+		err = emit(w, vm.Opushdata1, []byte{byte(n)})
+	} else if n < 0x10000 {
+		buf := make([]byte, 2)
+		binary.LittleEndian.PutUint16(buf, uint16(n))
+		err = emit(w, vm.Opushdata2, buf)
+	} else {
+		buf := make([]byte, 4)
+		binary.LittleEndian.PutUint32(buf, uint32(n))
+		err = emit(w, vm.Opushdata4, buf)
+	}
+	if err != nil {
+		return err
+	}
+	_, err = w.Write(b)
+	return err
+}
+
+func emitCall(w *bytes.Buffer, op vm.Opcode, label int16) error {
+	return emitJmp(w, op, label)
+}
+
+func emitJmp(w *bytes.Buffer, op vm.Opcode, label int16) error {
+	if !isOpcodeJmp(op) {
+		return fmt.Errorf("opcode %s is not a jump or call type", op)
+	}
+	buf := make([]byte, 2)
+	binary.LittleEndian.PutUint16(buf, uint16(label))
+	return emit(w, op, buf)
+}
+
+func isOpcodeJmp(op vm.Opcode) bool {
+	if op == vm.Ojmp || op == vm.Ojmpifnot || op == vm.Ojmpif || op == vm.Ocall {
+		return true
+	}
+	return false
+}