Add compactfloats directive

Add `//msgp:compactfloats` file directive, that will store float64 as float32, if it can be done so losslessly.

Boring, but correct replacement of #365

_generated/compactfloats.go

@@ -0,0 +1,19 @@
+package _generated
+
+//go:generate msgp
+
+//msgp:compactfloats
+
+//msgp:ignore F64
+type F64 float64
+
+//msgp:replace F64 with:float64
+
+type Floats struct {
+	A     float64
+	B     float32
+	Slice []float64
+	Map   map[string]float64
+	F     F64
+	OE    float64 `msg:",omitempty"`
+}

_generated/compactfloats_test.go

@@ -0,0 +1,78 @@
+package _generated
+
+import (
+	"bytes"
+	"reflect"
+	"testing"
+
+	"github.com/tinylib/msgp/msgp"
+)
+
+func TestCompactFloats(t *testing.T) {
+	// Constant that can be represented in f32 without loss
+	const f32ok = -1e2
+	allF32 := Floats{
+		A:     f32ok,
+		B:     f32ok,
+		Slice: []float64{f32ok, f32ok},
+		Map:   map[string]float64{"a": f32ok},
+		F:     f32ok,
+		OE:    f32ok,
+	}
+	asF32 := float32(f32ok)
+	wantF32 := map[string]any{"A": asF32, "B": asF32, "F": asF32, "Map": map[string]any{"a": asF32}, "OE": asF32, "Slice": []any{asF32, asF32}}
+
+	enc, err := allF32.MarshalMsg(nil)
+	if err != nil {
+		t.Error(err)
+	}
+	i, _, _ := msgp.ReadIntfBytes(enc)
+	got := i.(map[string]any)
+	if !reflect.DeepEqual(got, wantF32) {
+		t.Errorf("want: %v, got: %v (diff may be types)", wantF32, got)
+	}
+
+	var buf bytes.Buffer
+	en := msgp.NewWriter(&buf)
+	allF32.EncodeMsg(en)
+	en.Flush()
+	enc = buf.Bytes()
+	i, _, _ = msgp.ReadIntfBytes(enc)
+	got = i.(map[string]any)
+	if !reflect.DeepEqual(got, wantF32) {
+		t.Errorf("want: %v, got: %v (diff may be types)", wantF32, got)
+	}
+
+	const f64ok = -10e64
+	allF64 := Floats{
+		A:     f64ok,
+		B:     f32ok,
+		Slice: []float64{f64ok, f64ok},
+		Map:   map[string]float64{"a": f64ok},
+		F:     f64ok,
+		OE:    f64ok,
+	}
+	asF64 := float64(f64ok)
+	wantF64 := map[string]any{"A": asF64, "B": asF32, "F": asF64, "Map": map[string]any{"a": asF64}, "OE": asF64, "Slice": []any{asF64, asF64}}
+
+	enc, err = allF64.MarshalMsg(nil)
+	if err != nil {
+		t.Error(err)
+	}
+	i, _, _ = msgp.ReadIntfBytes(enc)
+	got = i.(map[string]any)
+	if !reflect.DeepEqual(got, wantF64) {
+		t.Errorf("want: %v, got: %v (diff may be types)", wantF64, got)
+	}
+
+	buf.Reset()
+	en = msgp.NewWriter(&buf)
+	allF64.EncodeMsg(en)
+	en.Flush()
+	enc = buf.Bytes()
+	i, _, _ = msgp.ReadIntfBytes(enc)
+	got = i.(map[string]any)
+	if !reflect.DeepEqual(got, wantF64) {
+		t.Errorf("want: %v, got: %v (diff may be types)", wantF64, got)
+	}
+}

gen/decode.go

@@ -29,7 +29,8 @@ func (d *decodeGen) needsField() {
 	d.hasfield = true
 }
 
-func (d *decodeGen) Execute(p Elem) error {
+func (d *decodeGen) Execute(p Elem, ctx Context) error {
+	d.ctx = &ctx
 	p = d.applyall(p)
 	if p == nil {
 		return nil
@@ -43,8 +44,6 @@ func (d *decodeGen) Execute(p Elem) error {
 		return nil
 	}
 
-	d.ctx = &Context{}
-
 	d.p.comment("DecodeMsg implements msgp.Decodable")
 
 	d.p.printf("\nfunc (%s %s) DecodeMsg(dc *msgp.Reader) (err error) {", p.Varname(), methodReceiver(p))

gen/encode.go

@@ -28,6 +28,10 @@ func (e *encodeGen) Apply(dirs []string) error {
 }
 
 func (e *encodeGen) writeAndCheck(typ string, argfmt string, arg interface{}) {
+	if e.ctx.compFloats && typ == "Float64" {
+		typ = "Float"
+	}
+
 	e.p.printf("\nerr = en.Write%s(%s)", typ, fmt.Sprintf(argfmt, arg))
 	e.p.wrapErrCheck(e.ctx.ArgsStr())
 }
@@ -47,7 +51,8 @@ func (e *encodeGen) Fuse(b []byte) {
 	}
 }
 
-func (e *encodeGen) Execute(p Elem) error {
+func (e *encodeGen) Execute(p Elem, ctx Context) error {
+	e.ctx = &ctx
 	if !e.p.ok() {
 		return e.p.err
 	}
@@ -59,8 +64,6 @@ func (e *encodeGen) Execute(p Elem) error {
 		return nil
 	}
 
-	e.ctx = &Context{}
-
 	e.p.comment("EncodeMsg implements msgp.Encodable")
 	rcv := imutMethodReceiver(p)
 	ogVar := p.Varname()

gen/marshal.go

@@ -27,7 +27,8 @@ func (m *marshalGen) Apply(dirs []string) error {
 	return nil
 }
 
-func (m *marshalGen) Execute(p Elem) error {
+func (m *marshalGen) Execute(p Elem, ctx Context) error {
+	m.ctx = &ctx
 	if !m.p.ok() {
 		return m.p.err
 	}
@@ -39,8 +40,6 @@ func (m *marshalGen) Execute(p Elem) error {
 		return nil
 	}
 
-	m.ctx = &Context{}
-
 	m.p.comment("MarshalMsg implements msgp.Marshaler")
 
 	// save the vname before
@@ -64,6 +63,9 @@ func (m *marshalGen) Execute(p Elem) error {
 }
 
 func (m *marshalGen) rawAppend(typ string, argfmt string, arg interface{}) {
+	if m.ctx.compFloats && typ == "Float64" {
+		typ = "Float"
+	}
 	m.p.printf("\no = msgp.Append%s(o, %s)", typ, fmt.Sprintf(argfmt, arg))
 }
 

gen/size.go

@@ -69,7 +69,8 @@ func (s *sizeGen) addConstant(sz string) {
 	panic("unknown size state")
 }
 
-func (s *sizeGen) Execute(p Elem) error {
+func (s *sizeGen) Execute(p Elem, ctx Context) error {
+	s.ctx = &ctx
 	if !s.p.ok() {
 		return s.p.err
 	}
@@ -81,7 +82,6 @@ func (s *sizeGen) Execute(p Elem) error {
 		return nil
 	}
 
-	s.ctx = &Context{}
 	s.ctx.PushString(p.TypeName())
 
 	s.p.comment("Msgsize returns an upper bound estimate of the number of bytes occupied by the serialized message")

gen/spec.go

@@ -75,7 +75,8 @@ const (
 )
 
 type Printer struct {
-	gens []generator
+	gens          []generator
+	CompactFloats bool
 }
 
 func NewPrinter(m Method, out io.Writer, tests io.Writer) *Printer {
@@ -144,7 +145,7 @@ func (p *Printer) Print(e Elem) error {
 		// collisions between idents created during SetVarname and idents created during Print,
 		// hence the separate prefixes.
 		resetIdent("zb")
-		err := g.Execute(e)
+		err := g.Execute(e, Context{compFloats: p.CompactFloats})
 		resetIdent("za")
 
 		if err != nil {
@@ -171,7 +172,8 @@ func (c contextVar) Arg() string {
 }
 
 type Context struct {
-	path []contextItem
+	path       []contextItem
+	compFloats bool
 }
 
 func (c *Context) PushString(s string) {
@@ -202,7 +204,7 @@ func (c *Context) ArgsStr() string {
 type generator interface {
 	Method() Method
 	Add(p TransformPass)
-	Execute(Elem) error // execute writes the method for the provided object.
+	Execute(Elem, Context) error // execute writes the method for the provided object.
 }
 
 type passes []TransformPass

gen/testgen.go

@@ -26,7 +26,7 @@ type mtestGen struct {
 	w io.Writer
 }
 
-func (m *mtestGen) Execute(p Elem) error {
+func (m *mtestGen) Execute(p Elem, _ Context) error {
 	p = m.applyall(p)
 	if p != nil && IsPrintable(p) {
 		switch p.(type) {
@@ -48,7 +48,7 @@ func etest(w io.Writer) *etestGen {
 	return &etestGen{w: w}
 }
 
-func (e *etestGen) Execute(p Elem) error {
+func (e *etestGen) Execute(p Elem, _ Context) error {
 	p = e.applyall(p)
 	if p != nil && IsPrintable(p) {
 		switch p.(type) {

gen/unmarshal.go

@@ -28,8 +28,9 @@ func (u *unmarshalGen) needsField() {
 	u.hasfield = true
 }
 
-func (u *unmarshalGen) Execute(p Elem) error {
+func (u *unmarshalGen) Execute(p Elem, ctx Context) error {
 	u.hasfield = false
+	u.ctx = &ctx
 	if !u.p.ok() {
 		return u.p.err
 	}
@@ -41,8 +42,6 @@ func (u *unmarshalGen) Execute(p Elem) error {
 		return nil
 	}
 
-	u.ctx = &Context{}
-
 	u.p.comment("UnmarshalMsg implements msgp.Unmarshaler")
 
 	u.p.printf("\nfunc (%s %s) UnmarshalMsg(bts []byte) (o []byte, err error) {", p.Varname(), methodReceiver(p))

msgp/write.go

@@ -346,6 +346,16 @@ func (mw *Writer) WriteNil() error {
 	return mw.push(mnil)
 }
 
+// WriteFloat writes a float to the writer as either float64
+// or float32 when it represents the exact same value
+func (mw *Writer) WriteFloat(f float64) error {
+	f32 := float32(f)
+	if float64(f32) == f {
+		return mw.prefix32(mfloat32, math.Float32bits(f32))
+	}
+	return mw.prefix64(mfloat64, math.Float64bits(f))
+}
+
 // WriteFloat64 writes a float64 to the writer
 func (mw *Writer) WriteFloat64(f float64) error {
 	return mw.prefix64(mfloat64, math.Float64bits(f))

msgp/write_bytes.go

@@ -60,6 +60,16 @@ func AppendArrayHeader(b []byte, sz uint32) []byte {
 // AppendNil appends a 'nil' byte to the slice
 func AppendNil(b []byte) []byte { return append(b, mnil) }
 
+// AppendFloat appends a float to the slice as either float64
+// or float32 when it represents the exact same value
+func AppendFloat(b []byte, f float64) []byte {
+	f32 := float32(f)
+	if float64(f32) == f {
+		return AppendFloat32(b, f32)
+	}
+	return AppendFloat64(b, f)
+}
+
 // AppendFloat64 appends a float64 to the slice
 func AppendFloat64(b []byte, f float64) []byte {
 	o, n := ensure(b, Float64Size)

msgp/write_bytes_test.go

@@ -3,6 +3,7 @@ package msgp
 import (
 	"bytes"
 	"math"
+	"math/rand"
 	"reflect"
 	"strings"
 	"testing"
@@ -134,6 +135,74 @@ func TestAppendNil(t *testing.T) {
 	}
 }
 
+func TestAppendFloat(t *testing.T) {
+	rng := rand.New(rand.NewSource(0))
+	const n = 1e7
+	src := make([]float64, n)
+	for i := range src {
+		// ~50% full float64, 50% converted from float32.
+		if rng.Uint32()&1 == 1 {
+			src[i] = rng.NormFloat64()
+		} else {
+			src[i] = float64(math.MaxFloat32 * (0.5 - rng.Float32()))
+		}
+	}
+
+	var buf bytes.Buffer
+	en := NewWriter(&buf)
+
+	var bts []byte
+	for _, f := range src {
+		en.WriteFloat(f)
+		bts = AppendFloat(bts, f)
+	}
+	en.Flush()
+	if buf.Len() != len(bts) {
+		t.Errorf("encoder wrote %d; append wrote %d bytes", buf.Len(), len(bts))
+	}
+	t.Logf("%f bytes/value", float64(buf.Len())/n)
+	a, b := bts, buf.Bytes()
+	for i := range a {
+		if a[i] != b[i] {
+			t.Errorf("mismatch at byte %d, %d != %d", i, a[i], b[i])
+			break
+		}
+	}
+
+	for i, want := range src {
+		var got float64
+		var err error
+		got, a, err = ReadFloat64Bytes(a)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if want != got {
+			t.Errorf("value #%d: want %v; got %v", i, want, got)
+		}
+	}
+}
+
+func BenchmarkAppendFloat(b *testing.B) {
+	rng := rand.New(rand.NewSource(0))
+	const n = 1 << 16
+	src := make([]float64, n)
+	for i := range src {
+		// ~50% full float64, 50% converted from float32.
+		if rng.Uint32()&1 == 1 {
+			src[i] = rng.NormFloat64()
+		} else {
+			src[i] = float64(math.MaxFloat32 * (0.5 - rng.Float32()))
+		}
+	}
+	buf := make([]byte, 0, 9)
+	b.SetBytes(8)
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		AppendFloat64(buf, src[i&(n-1)])
+	}
+}
+
 func TestAppendFloat64(t *testing.T) {
 	f := float64(3.14159)
 	var buf bytes.Buffer