WIP encoding values

Makefile

@@ -1,6 +1,6 @@
 default: test
 
-generated = tokentype_string.go opcode_string.go testapi_test.go
+generated = tokentype_string.go opcode_string.go typecode_string.go testapi_test.go
 
 bcl: stringer $(generated) go.mod go.sum *.go cmd/bcl/*.go
 	go build ./cmd/bcl
@@ -11,6 +11,9 @@ tokentype_string.go: token.go
 opcode_string.go: opcode.go
 	go generate
 
+typecode_string.go: typecode.go
+	go generate
+
 testapi_test.go: test.py basic_test.go
 	go generate && go fmt testapi_test.go
 

encoding.go

@@ -1,6 +1,12 @@
 package bcl
 
-import "github.com/mohae/uvarint"
+import (
+	stdbinary "encoding/binary"
+	"fmt"
+	"math"
+
+	"github.com/mohae/uvarint"
+)
 
 func u16ToBytes(p []byte, x uint16) {
 	p[0] = byte(x >> 8 & 0xff)
@@ -18,3 +24,116 @@ func uvarintToBytes(p []byte, x uint64) int {
 func uvarintFromBytes(p []byte) (uint64, int) {
 	return uvarint.Decode(p)
 }
+
+func varintToBytes(p []byte, x int64) int {
+	return uvarintToBytes(p, i64ToU64(x))
+}
+
+func varintFromBytes(p []byte) (int64, int) {
+	u, n := uvarintFromBytes(p)
+	return u64ToI64(u), n
+}
+
+func i64ToU64(x int64) uint64 {
+	if x < 0 {
+		return uint64(-x) ^ 0xffffffffffffffff + 1
+	}
+	return uint64(x)
+}
+
+func u64ToI64(x uint64) int64 {
+	if x > math.MaxInt64 {
+		return -(int64(x^0xffffffffffffffff) + 1)
+	}
+	return int64(x)
+}
+
+func valueToBytes(p []byte, v value) (n int) {
+	p[0] = byte(typecodeOf(v))
+	p = p[1:] // local copy
+	n++
+
+	switch x := v.(type) {
+	case int:
+		n += varintToBytes(p, int64(x))
+
+	case float64:
+		stdbinary.BigEndian.PutUint64(p, math.Float64bits(x))
+		n += 8
+
+	case string:
+		i := uvarintToBytes(p, uint64(len(x)))
+		p = p[i:]
+		if len(p) < len(x) {
+			n += i
+			panic("no space ")
+		}
+		copy(p, []byte(x))
+		n += i + len(x)
+
+	case bool:
+		if x {
+			p[0] = 1
+		} else {
+			p[0] = 0
+		}
+		n++
+
+	default:
+		// whether it's nil or invalid type, don't emit the value
+	}
+	return n
+}
+
+func valueFromBytes(p []byte) (value, int) {
+	switch c, p := typecode(p[0]), p[1:]; c {
+	case typeINT:
+		x, n := varintFromBytes(p)
+		return int(x), 1 + n
+
+	case typeFLOAT:
+		return math.Float64frombits(stdbinary.BigEndian.Uint64(p)), 1 + 8
+
+	case typeSTR:
+		k, i := uvarintFromBytes(p)
+		return string(p[i : i+int(k)]), 1 + i + int(k)
+
+	case typeBOOL:
+		return p[0] != 0, 1 + 1
+
+	case typeNIL:
+		return nil, 1
+
+	default:
+		panic(errInvalidType{p[0]})
+	}
+}
+
+func typecodeOf(v value) typecode {
+	switch v.(type) {
+	case int:
+		return typeINT
+	case float64:
+		return typeFLOAT
+	case string:
+		return typeSTR
+	case bool:
+		return typeBOOL
+	default:
+		if v == nil {
+			return typeNIL
+		}
+		panic(errInvalidValue{v})
+	}
+}
+
+type errInvalidType struct{ byte }
+type errInvalidValue struct{ value }
+
+func (e errInvalidType) Error() string {
+	return fmt.Sprintf("invalid type: %q", e.byte)
+}
+
+func (e errInvalidValue) Error() string {
+	return fmt.Sprintf("invalid value: %v", e.value)
+}

encoding_test.go

@@ -0,0 +1,111 @@
+package bcl
+
+import (
+	"math"
+	"testing"
+	"testing/quick"
+)
+
+var qcConf = &quick.Config{MaxCount: 1000}
+
+func TestEncodingU16(t *testing.T) {
+	f := func(x uint16) bool {
+		var b [2]byte
+		var p []byte = b[:]
+		u16ToBytes(p, x)
+		return x == u16FromBytes(p)
+	}
+	if err := quick.Check(f, qcConf); err != nil {
+		t.Error(err)
+	}
+}
+
+func TestEncodingUvarint(t *testing.T) {
+	f := func(x uint64) bool {
+		var b [9]byte
+		var p []byte = b[:]
+		n := uvarintToBytes(p, x)
+		y, m := uvarintFromBytes(p)
+		return n == m && x == y
+	}
+	if err := quick.Check(f, qcConf); err != nil {
+		t.Error(err)
+	}
+}
+
+func TestEncodingVarint(t *testing.T) {
+	f := func(x int64) bool {
+		var b [9]byte
+		var p []byte = b[:]
+		n := varintToBytes(p, x)
+		y, m := varintFromBytes(p)
+		return n == m && x == y
+	}
+	if err := quick.Check(f, qcConf); err != nil {
+		t.Error(err)
+	}
+}
+
+func testEncodingValue(t *testing.T, x value) {
+	t.Helper()
+
+	var b [12]byte // for the longest string below
+	var p []byte = b[:]
+
+	n := valueToBytes(p, x)
+	y, m := valueFromBytes(p)
+
+	if n != m {
+		t.Errorf("x=%v: size mismatch n=%d m=%d", x, n, m)
+	}
+	if x != y {
+		t.Errorf("mismatch x=%v y=%v", x, y)
+	}
+}
+
+func TestEncodingValuesTab(t *testing.T) {
+	tab := []value{
+		nil,
+		0, 1, 2, -1, -2, 10, 127, 128, -127, -128,
+		math.MaxInt64, math.MaxInt64 - 1, math.MinInt64, math.MinInt64 + 1,
+		0.0, 0.5, -0.5, 1234.5, -1234.5,
+		math.MaxFloat64, -math.MaxFloat64,
+		true, false,
+		"", "foo", "1234567890",
+	}
+	for _, v := range tab {
+		testEncodingValue(t, v)
+	}
+}
+
+func qcEncodingValue(x value) bool {
+	var b [11]byte
+	var p []byte = b[:]
+
+	n := valueToBytes(p, x)
+	y, m := valueFromBytes(p)
+
+	return n == m && x == y
+}
+
+func qcEncodingString(s string) bool {
+	p := make([]byte, 1+9+len(s))
+
+	n := valueToBytes(p, s)
+	y, m := valueFromBytes(p)
+
+	return n == m && s == y
+}
+
+func TestEncodingValuesQC(t *testing.T) {
+	var (
+		fInt    = func(x int) bool { return qcEncodingValue(x) }
+		fFloat  = func(x float64) bool { return qcEncodingValue(x) }
+		fString = func(x string) bool { return qcEncodingString(x) }
+	)
+	for _, f := range []any{fInt, fFloat, fString} {
+		if err := quick.Check(f, qcConf); err != nil {
+			t.Error(err)
+		}
+	}
+}

typecode.go

@@ -0,0 +1,13 @@
+package bcl
+
+type typecode byte
+
+const (
+	typeNIL typecode = iota
+	typeINT
+	typeFLOAT
+	typeSTR
+	typeBOOL
+)
+
+//go:generate stringer -type typecode -trimprefix type