cryptobyte: add ReadUint64 and AddUint64

Fixes golang/go#53481.

Change-Id: Ic00eef498d1d3b5b0ca5c9c526fac7c26de30cf2
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/421014
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
Run-TryBot: hopehook <hopehook@qq.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>

cryptobyte/builder.go

@@ -95,6 +95,11 @@ func (b *Builder) AddUint32(v uint32) {
 	b.add(byte(v>>24), byte(v>>16), byte(v>>8), byte(v))
 }
 
+// AddUint64 appends a big-endian, 64-bit value to the byte string.
+func (b *Builder) AddUint64(v uint64) {
+	b.add(byte(v>>56), byte(v>>48), byte(v>>40), byte(v>>32), byte(v>>24), byte(v>>16), byte(v>>8), byte(v))
+}
+
 // AddBytes appends a sequence of bytes to the byte string.
 func (b *Builder) AddBytes(v []byte) {
 	b.add(v...)

cryptobyte/cryptobyte_test.go

@@ -141,7 +141,7 @@ func TestUint24(t *testing.T) {
 	var s String = b.BytesOrPanic()
 	var v uint32
 	if !s.ReadUint24(&v) {
-		t.Error("ReadUint8() = false, want true")
+		t.Error("ReadUint24() = false, want true")
 	}
 	if v != 0xfffefd {
 		t.Errorf("v = %d, want fffefd", v)
@@ -169,7 +169,7 @@ func TestUint32(t *testing.T) {
 	var s String = b.BytesOrPanic()
 	var v uint32
 	if !s.ReadUint32(&v) {
-		t.Error("ReadUint8() = false, want true")
+		t.Error("ReadUint32() = false, want true")
 	}
 	if v != 0xfffefdfc {
 		t.Errorf("v = %x, want fffefdfc", v)
@@ -179,6 +179,26 @@ func TestUint32(t *testing.T) {
 	}
 }
 
+func TestUint64(t *testing.T) {
+	var b Builder
+	b.AddUint64(0xf2fefefcff3cfdfc)
+	if err := builderBytesEq(&b, 242, 254, 254, 252, 255, 60, 253, 252); err != nil {
+		t.Error(err)
+	}
+
+	var s String = b.BytesOrPanic()
+	var v uint64
+	if !s.ReadUint64(&v) {
+		t.Error("ReadUint64() = false, want true")
+	}
+	if v != 0xf2fefefcff3cfdfc {
+		t.Errorf("v = %x, want f2fefefcff3cfdfc", v)
+	}
+	if len(s) != 0 {
+		t.Errorf("len(s) = %d, want 0", len(s))
+	}
+}
+
 func TestUMultiple(t *testing.T) {
 	var b Builder
 	b.AddUint8(23)

cryptobyte/string.go

@@ -81,6 +81,17 @@ func (s *String) ReadUint32(out *uint32) bool {
 	return true
 }
 
+// ReadUint64 decodes a big-endian, 64-bit value into out and advances over it.
+// It reports whether the read was successful.
+func (s *String) ReadUint64(out *uint64) bool {
+	v := s.read(8)
+	if v == nil {
+		return false
+	}
+	*out = uint64(v[0])<<56 | uint64(v[1])<<48 | uint64(v[2])<<40 | uint64(v[3])<<32 | uint64(v[4])<<24 | uint64(v[5])<<16 | uint64(v[6])<<8 | uint64(v[7])
+	return true
+}
+
 func (s *String) readUnsigned(out *uint32, length int) bool {
 	v := s.read(length)
 	if v == nil {