lib/bytes: add function to convert hexadecimal into byte

2 files changed, 76 insertions, 0 deletions

diff --git a/lib/bytes/bytes.go b/lib/bytes/bytes.go
index d1fee2c4..55c8a308 100644
--- a/lib/bytes/bytes.go
+++ b/lib/bytes/bytes.go
@@ -254,6 +254,36 @@ func PrintHex(title string, data []byte, col int) {
 }
 
 //
+// ReadHexByte read two characters from data start from index "x" and convert
+// them to byte.
+//
+func ReadHexByte(data []byte, x int) (b byte, ok bool) {
+	if len(data) < x+2 {
+		return 0, false
+	}
+	var y uint = 4
+	for {
+		switch {
+		case data[x] >= '0' && data[x] <= '9':
+			b |= byte(data[x]-'0') << y
+		case data[x] >= 'A' && data[x] <= 'F':
+			b |= byte(data[x]-('A'-10)) << y
+		case data[x] >= 'a' && data[x] <= 'f':
+			b |= byte(data[x]-('a'-10)) << y
+		default:
+			return b, false
+		}
+		if y == 0 {
+			break
+		}
+		y -= 4
+		x++
+	}
+
+	return b, true
+}
+
+//
 // ReadInt16 will convert two bytes from data start at `x` into int16 and
 // return it.
 //
diff --git a/lib/bytes/bytes_test.go b/lib/bytes/bytes_test.go
index 3b79aced..2e1b3a24 100644
--- a/lib/bytes/bytes_test.go
+++ b/lib/bytes/bytes_test.go
@@ -164,6 +164,52 @@ func TestIsTokenAt(t *testing.T) {
 	}
 }
 
+func TestReadHexByte(t *testing.T) {
+	cases := []struct {
+		in    []byte
+		exp   byte
+		expOK bool
+	}{{
+		in: []byte{},
+	}, {
+		in: []byte("x0"),
+	}, {
+		in: []byte("0x"),
+	}, {
+		in:    []byte("00"),
+		expOK: true,
+	}, {
+		in:    []byte("01"),
+		exp:   1,
+		expOK: true,
+	}, {
+		in:    []byte("10"),
+		exp:   16,
+		expOK: true,
+	}, {
+		in:    []byte("1A"),
+		exp:   26,
+		expOK: true,
+	}, {
+		in:    []byte("1a"),
+		exp:   26,
+		expOK: true,
+	}, {
+		in:    []byte("a1"),
+		exp:   161,
+		expOK: true,
+	}}
+
+	for _, c := range cases {
+		t.Log(c.in)
+
+		got, ok := ReadHexByte(c.in, 0)
+
+		test.Assert(t, "b", c.exp, got, true)
+		test.Assert(t, "ok", c.expOK, ok, true)
+	}
+}
+
 func TestSkipAfterToken(t *testing.T) {
 	line := []byte(`abc \def ghi`)