compiler!

code/code.go

@@ -0,0 +1,116 @@
+package code
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+)
+
+type Instructions []byte
+
+type Opcode byte
+
+const (
+	OpConstant Opcode = iota
+)
+
+type Definition struct {
+	Name          string
+	OperandWidths []int
+}
+
+var definitions = map[Opcode]*Definition{
+	OpConstant: {"OpConstant", []int{2}},
+}
+
+func Lookup(op byte) (*Definition, error) {
+	def, ok := definitions[Opcode(op)]
+	if !ok {
+		return nil, fmt.Errorf("opcode %d undefined", op)
+	}
+
+	return def, nil
+}
+
+func Make(op Opcode, operands ...int) []byte {
+	def, ok := definitions[op]
+	if !ok {
+		return []byte{}
+	}
+
+	instructions := 1
+	for _, w := range def.OperandWidths {
+		instructions += w
+	}
+
+	instruction := make([]byte, instructions)
+	instruction[0] = byte(op)
+
+	offset := 1
+	for i, o := range operands {
+		width := def.OperandWidths[i]
+		switch width {
+		case 2:
+			binary.BigEndian.PutUint16(instruction[offset:], uint16(o))
+		}
+		offset += width
+	}
+
+	return instruction
+}
+
+func (ins Instructions) String() string {
+	var out bytes.Buffer
+
+	i := 0
+	for i < len(ins) {
+		def, err := Lookup(ins[i])
+		if err != nil {
+			fmt.Fprintf(&out, "ERROR: %s\n", err)
+			continue
+		}
+
+		operands, read := ReadOperands(def, ins[i+1:])
+
+		fmt.Fprintf(&out, "%04d %s\n", i, ins.fmtInstruction(def, operands))
+
+		i += 1 + read
+	}
+
+	return out.String()
+}
+
+func (ins Instructions) fmtInstruction(def *Definition, operands []int) string {
+	operandCount := len(def.OperandWidths)
+
+	if len(operands) != operandCount {
+		return fmt.Sprintf("ERROR: operand len %d does not match defined %d\n", len(operands), operandCount)
+	}
+
+	switch operandCount {
+	case 1:
+		return fmt.Sprintf("%s %d", def.Name, operands[0])
+	}
+
+	return fmt.Sprintf("ERROR: unhandled operandCount for %s\n", def.Name)
+}
+
+func ReadOperands(def *Definition, ins Instructions) ([]int, int) {
+	operands := make([]int, len(def.OperandWidths))
+	offset := 0
+
+	for i, width := range def.OperandWidths {
+		switch width {
+		case 2:
+			operands[i] = int(ReadUint16(ins[offset:]))
+		}
+
+		offset += width
+	}
+
+	return operands, offset
+}
+
+func ReadUint16(ins Instructions) uint16 {
+	return binary.BigEndian.Uint16(ins)
+}

code/code_test.go

@@ -0,0 +1,79 @@
+package code
+
+import "testing"
+
+func TestMake(t *testing.T) {
+	test := []struct {
+		op       Opcode
+		operands []int
+		expected []byte
+	}{
+		{OpConstant, []int{65534}, []byte{byte(OpConstant), 255, 254}},
+	}
+
+	for _, tt := range test {
+		instructions := Make(tt.op, tt.operands...)
+
+		if len(instructions) != len(tt.expected) {
+			t.Errorf("instruction has wrong length. want=%d, got=%d", len(tt.expected), len(instructions))
+		}
+
+		for i, b := range tt.expected {
+			if instructions[i] != tt.expected[i] {
+				t.Errorf("wrong byte at pos %d. want=%d, got=%d", i, b, instructions[i])
+			}
+		}
+	}
+}
+
+func TestInstructions(t *testing.T) {
+	instructions := []Instructions{
+		Make(OpConstant, 1),
+		Make(OpConstant, 2),
+		Make(OpConstant, 65535),
+	}
+
+	expected := `0000 OpConstant 1
+0003 OpConstant 2
+0006 OpConstant 65535
+`
+
+	concatted := Instructions{}
+	for _, ins := range instructions {
+		concatted = append(concatted, ins...)
+	}
+
+	if concatted.String() != expected {
+		t.Errorf("instructions wrong formatted.\nwant=%q\ngot=%q", expected, concatted.String())
+	}
+}
+
+func TestOperands(t *testing.T) {
+	tests := []struct {
+		op        Opcode
+		operands  []int
+		bytesRead int
+	}{
+		{OpConstant, []int{65535}, 2},
+	}
+
+	for _, tt := range tests {
+		instruction := Make(tt.op, tt.operands...)
+
+		def, err := Lookup(byte(tt.op))
+		if err != nil {
+			t.Fatalf("definition not found: %q\n", err)
+		}
+
+		operandsRead, n := ReadOperands(def, instruction[1:])
+		if n != tt.bytesRead {
+			t.Fatalf("n wrong. want=%d, got=%d", tt.bytesRead, n)
+		}
+
+		for i, want := range tt.operands {
+			if operandsRead[i] != want {
+				t.Errorf("operand wrong. want=%d, got=%d", want, operandsRead[i])
+			}
+		}
+	}
+}