diff --git a/ryu.go b/ryu.go
index f149243..833fe7b 100644
--- a/ryu.go
+++ b/ryu.go
@@ -78,17 +78,17 @@ func AppendFloat32(b []byte, f float32) []byte {
 func FormatFloat64(f float64) string {
 	b := make([]byte, 0, 24)
 	b = AppendFloat64(b, f)
+	return byteSliceToString(b)
+}
 
-	// Convert the output to a string without copying.
-	var s string
-	sh := (*reflect.StringHeader)(unsafe.Pointer(&s))
-	sh.Data = uintptr(unsafe.Pointer(&b[0]))
-	sh.Len = len(b)
-	return s
+func byteSliceToString(b []byte) string {
+	// Zero alloc conversion following pattern found in stdlib strings.Builder.
+	return *(*string)(unsafe.Pointer(&b))
 }
 
 // AppendFloat64 appends the string form of the 64-bit floating point number f,
 // as generated by FormatFloat64, to b and returns the extended buffer.
+// It behaves like strconv.AppendFloat(b, f, 'e', -1, 64).
 func AppendFloat64(b []byte, f float64) []byte {
 	// Step 1: Decode the floating-point number.
 	// Unify normalized and subnormal cases.
@@ -126,6 +126,54 @@ func appendSpecial(b []byte, neg, expZero, mantZero bool) []byte {
 	return append(b, "0e+00"...)
 }
 
+// FormatFloat64 converts a 64-bit floating point number f to a string.
+// It behaves like strconv.FormatFloat(f, 'f', -1, 64).
+func FormatFloat64f(f float64) string {
+	b := make([]byte, 0, 24)
+	b = AppendFloat64f(b, f)
+	return byteSliceToString(b)
+}
+
+// AppendFloat64 appends the string form of the 64-bit floating point number f,
+// as generated by FormatFloat64, to b and returns the extended buffer.
+// It behaves like strconv.AppendFloat(b, f, 'f', -1, 64).
+func AppendFloat64f(b []byte, f float64) []byte {
+	// Step 1: Decode the floating-point number.
+	// Unify normalized and subnormal cases.
+	u := math.Float64bits(f)
+	neg := u>>(mantBits64+expBits64) != 0
+	mant := u & (uint64(1)<<mantBits64 - 1)
+	exp := (u >> mantBits64) & (uint64(1)<<expBits64 - 1)
+
+	// Exit early for easy cases.
+	if exp == uint64(1)<<expBits64-1 || (exp == 0 && mant == 0) {
+		return appendSpecialf(b, neg, exp == 0, mant == 0)
+	}
+
+	d, ok := float64ToDecimalExactInt(mant, exp)
+	if !ok {
+		d = float64ToDecimal(mant, exp)
+	}
+	return d.appendF(b, neg)
+}
+
+func appendSpecialf(b []byte, neg, expZero, mantZero bool) []byte {
+	if !mantZero {
+		return append(b, "NaN"...)
+	}
+	if !expZero {
+		if neg {
+			return append(b, "-Inf"...)
+		} else {
+			return append(b, "+Inf"...)
+		}
+	}
+	if neg {
+		b = append(b, '-')
+	}
+	return append(b, '0')
+}
+
 func assert(t bool, msg string) {
 	if !t {
 		panic(msg)
diff --git a/ryu64.go b/ryu64.go
index 87dfb8b..9c49c3b 100644
--- a/ryu64.go
+++ b/ryu64.go
@@ -102,6 +102,77 @@ func (d dec64) append(b []byte, neg bool) []byte {
 	return b
 }
 
+func sizeSlice(b []byte, bufLen int) []byte {
+	if cap(b)-len(b) >= bufLen {
+		// Avoid function call in the common case.
+		return b[:len(b)+bufLen]
+	}
+
+	return append(b, make([]byte, bufLen)...)
+}
+
+func (d dec64) appendF(b []byte, neg bool) []byte {
+	// Step 5: Print the decimal representation.
+	if neg {
+		b = append(b, '-')
+	}
+
+	out := d.m
+	outLen := decimalLen64(out)
+
+	dE := int(d.e)
+	if dE >= 0 {
+		// XYZ
+		n := len(b)
+		b = sizeSlice(b, dE+outLen)
+		for i := n; i < dE+n; i++ {
+			b[outLen+i] = '0'
+		}
+
+		for i := n + outLen - 1; i >= n; i-- {
+			b[i] = '0' + byte(out%10)
+			out /= 10
+		}
+
+		return b
+	}
+
+	ePos := -dE
+	if ePos >= outLen {
+		// 0.XYZ
+		b := append(b, "0."...)
+		n := len(b)
+		b = sizeSlice(b, ePos)
+		for i := n + ePos - 1; i >= n; i-- {
+			b[i] = '0' + byte(out%10)
+			out /= 10
+		}
+
+		return b
+	}
+
+	// Y.XZ
+	b = sizeSlice(b, outLen+1) // + "."
+	n := len(b)
+	i := n - 1
+	end := i - outLen
+	for ; ePos > 0; i-- {
+		b[i] = '0' + byte(out%10)
+		out /= 10
+		ePos--
+	}
+
+	b[i] = '.'
+	i--
+
+	for ; i >= end; i-- {
+		b[i] = '0' + byte(out%10)
+		out /= 10
+	}
+
+	return b
+}
+
 func float64ToDecimalExactInt(mant, exp uint64) (d dec64, ok bool) {
 	e := exp - bias64
 	if e > mantBits64 {
diff --git a/ryu_test.go b/ryu_test.go
index e897c56..a85999b 100644
--- a/ryu_test.go
+++ b/ryu_test.go
@@ -44,6 +44,7 @@ var genericTestCases = []float64{
 	-0.3,
 	1000000,
 	123456.7,
+	10.01,
 	123e45,
 	-123.45,
 	1e23,
@@ -191,8 +192,10 @@ var benchCases = []float64{
 	0,
 	1,
 	0.3,
+	0.0000000003,
 	1000000,
 	-123.45,
+	-123456789.123456789,
 }
 
 func BenchmarkAppendFloat32(b *testing.B) {
@@ -319,3 +322,49 @@ func measureCall(b []byte, f float64, format func([]byte, float64) []byte, times
 	elapsed := time.Since(start)
 	return elapsed / time.Duration(times)
 }
+
+func TestFormatFloat64f(t *testing.T) {
+	for _, f := range append(genericTestCases, float64TestCases...) {
+		got := FormatFloat64f(f)
+		want := strconv.FormatFloat(f, 'f', -1, 64)
+		if got != want {
+			t.Errorf("FormatFloat64f(%g): got %q; want %q", f, got, want)
+		}
+	}
+}
+
+func TestAppendFloat64f(t *testing.T) {
+	for _, f := range append(genericTestCases, float64TestCases...) {
+		// Test with under sized and over sized buffer since the implementation
+		// differs a bit between the two cases.
+		bigBufResult := string(AppendFloat64f(make([]byte, 0, 1000), f))
+		smallBufResult := string(AppendFloat64f(make([]byte, 0), f))
+		if bigBufResult != smallBufResult {
+			t.Errorf("AppendFloat64f(%g): big %q; small %q", f, bigBufResult, smallBufResult)
+		}
+	}
+}
+
+func BenchmarkStrconvAppendFloat64f(b *testing.B) {
+	for _, f := range append(benchCases, benchCases64...) {
+		b.Run(FormatFloat64(f), func(b *testing.B) {
+			var buf []byte
+			for i := 0; i < b.N; i++ {
+				buf = strconv.AppendFloat(buf[:0], f, 'f', -1, 64)
+			}
+			sinkb = buf
+		})
+	}
+}
+
+func BenchmarkAppendFloat64f(b *testing.B) {
+	for _, f := range append(benchCases, benchCases64...) {
+		b.Run(FormatFloat64(f), func(b *testing.B) {
+			var buf []byte
+			for i := 0; i < b.N; i++ {
+				buf = AppendFloat64f(buf[:0], f)
+			}
+			sinkb = buf
+		})
+	}
+}