misc: code refactor

Author: tinycedar

instructions/bytecode_reader.go

@@ -0,0 +1,40 @@
+package instructions
+
+type CodeReader struct {
+	code   []byte
+	offset int
+}
+
+func NewByteCodeReader(code []byte, offset int) *CodeReader {
+	return &CodeReader{code, offset}
+}
+
+func (r *CodeReader) Offset() int {
+	return r.offset
+}
+
+func (r *CodeReader) ReadUint8() uint8 {
+	return uint8(r.ReadBytes(1)[0])
+}
+
+func (r *CodeReader) ReadUint16() uint16 {
+	byte1 := uint16(r.ReadUint8())
+	byte2 := uint16(r.ReadUint8())
+	return (byte1 << 8) | byte2
+}
+
+func (r *CodeReader) ReadInt8() int8 {
+	return int8(r.ReadBytes(1)[0])
+}
+
+func (r *CodeReader) ReadInt16() int16 {
+	byte1 := int16(r.ReadUint8())
+	byte2 := int16(r.ReadUint8())
+	return (byte1 << 8) | byte2
+}
+
+func (r *CodeReader) ReadBytes(len int) []byte {
+	result := r.code[r.offset : r.offset+len]
+	r.offset += len
+	return result
+}

instructions/code_reader.go

@@ -0,0 +1,14 @@
+package comparisons
+
+import (
+	"github.com/tinycedar/vanilla/instructions"
+)
+
+func FetchInstruction(opCode uint8, reader *instructions.CodeReader) instructions.Instruction {
+	switch opCode {
+	case 0xa2:
+		return &if_icmpge{opCode, reader.ReadUint16()}
+	default:
+		return instructions.NewNotImplemented(opCode)
+	}
+}

instructions/comparisons/comparisons.go

@@ -0,0 +1,18 @@
+package comparisons
+
+import (
+	"github.com/tinycedar/vanilla/runtime/thread"
+)
+
+type if_icmpge struct {
+	opCode uint8
+	offset uint16
+}
+
+func (i *if_icmpge) Execute(f *thread.Frame) {
+	value2 := f.OperandStack().PopInt()
+	value1 := f.OperandStack().PopInt()
+	if value1 >= value2 {
+		f.SetPC(f.GetPC() + int(i.offset))
+	}
+}

instructions/comparisons/if_icmpge.go

@@ -0,0 +1,22 @@
+package constants
+
+import (
+	"github.com/tinycedar/vanilla/instructions"
+)
+
+func FetchInstruction(opCode uint8, reader *instructions.CodeReader) instructions.Instruction {
+	switch opCode {
+	case 0x03:
+		return &iconst_0{opCode}
+	case 0x04:
+		return &iconst_1{opCode}
+	case 0x05:
+		return &iconst_2{opCode}
+	case 0x10:
+		return &bipush{opCode, reader.ReadInt8()}
+	case 0x12:
+		return &ldc{opCode, reader.ReadUint8()}
+	default:
+		return instructions.NewNotImplemented(opCode)
+	}
+}

instructions/constants/constants.go

@@ -1,10 +1,14 @@
-package instructions
+package constants
 
 import (
 	"fmt"
 	"github.com/tinycedar/vanilla/runtime/thread"
 )
 
+type iconst_0 struct {
+	opCode uint8
+}
+
 type iconst_1 struct {
 	opCode uint8
 }
@@ -13,6 +17,14 @@ type iconst_2 struct {
 	opCode uint8
 }
 
+func (i *iconst_0) Execute(f *thread.Frame) {
+	f.OperandStack().PushInt(0)
+}
+
+func (i *iconst_0) String() string {
+	return fmt.Sprintf("{opcode: 0x%x, iconst_0}", i.opCode)
+}
+
 func (i *iconst_1) Execute(f *thread.Frame) {
 	f.OperandStack().PushInt(1)
 }
@@ -28,3 +40,16 @@ func (i *iconst_2) Execute(f *thread.Frame) {
 func (i *iconst_2) String() string {
 	return fmt.Sprintf("{opcode: 0x%x, iconst_2}", i.opCode)
 }
+
+type bipush struct {
+	opCode uint8
+	value  int8
+}
+
+func (i *bipush) Execute(f *thread.Frame) {
+	f.OperandStack().PushInt(int32(i.value))
+}
+
+func (i *bipush) String() string {
+	return fmt.Sprintf("{opcode: 0x%x, bipush}", i.opCode)
+}

instructions/const.go renamed to instructions/constants/iconst.go

@@ -1,4 +1,4 @@
-package instructions
+package constants
 
 import (
 	"fmt"

instructions/ldc.go renamed to instructions/constants/ldc.go

@@ -0,0 +1,18 @@
+package control
+
+import (
+	"github.com/tinycedar/vanilla/instructions"
+)
+
+func FetchInstruction(opCode uint8, reader *instructions.CodeReader) instructions.Instruction {
+	switch opCode {
+	case 0xa7:
+		return &_goto{opCode, reader.ReadInt16()}
+	case 0xac:
+		return &ireturn{opCode}
+	case 0xb1:
+		return &_return{opCode}
+	default:
+		return instructions.NewNotImplemented(opCode)
+	}
+}

instructions/control/control.go

@@ -0,0 +1,14 @@
+package control
+
+import (
+	"github.com/tinycedar/vanilla/runtime/thread"
+)
+
+type _goto struct {
+	opCode     uint8
+	branchoffs int16
+}
+
+func (i *_goto) Execute(f *thread.Frame) {
+	f.SetPC(f.GetPC() + int(i.branchoffs))
+}

instructions/control/goto.go

@@ -1,10 +1,20 @@
-package instructions
+package control
 
 import (
 	"fmt"
 	"github.com/tinycedar/vanilla/runtime/thread"
 )
 
+type ireturn struct {
+	opCode uint8
+}
+
+func (i *ireturn) Execute(f *thread.Frame) {
+	val := f.OperandStack().PopInt()
+	f.NextFrame().OperandStack().PushInt(val)
+	f.Thread().Pop()
+}
+
 type _return struct {
 	opCode uint8
 }