base64: add encode

base64/base64.v

@@ -47,3 +47,49 @@ fn decode(data string) string {
 	return tos(str, str_len+2)
 }
 
+const (
+	EncodingTable = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
+)
+
+fn encode(data string) string {
+	input_length := data.len
+	output_length := 4 * ((input_length + 2) / 3)
+
+	mut i := 0
+	mut j := 0
+	mut str := malloc(output_length)
+
+	for i < input_length {
+		mut octet_a := 0
+		mut octet_b := 0
+		mut octet_c := 0
+
+		if i < input_length {
+			octet_a = int(data[i])
+			i++
+		}
+		if i < input_length {
+			octet_b = int(data[i])
+			i++
+		}
+		if i < input_length {
+			octet_c = int(data[i])
+			i++
+		}
+
+		triple := ((octet_a << 0x10) + (octet_b << 0x08) + octet_c)
+
+		str[j+0] = EncodingTable[(triple >> 3 * 6) & 63] // 63 is 0x3F
+		str[j+1] = EncodingTable[(triple >> 2 * 6) & 63]
+		str[j+2] = EncodingTable[(triple >> 1 * 6) & 63]
+		str[j+3] = EncodingTable[(triple >> 0 * 6) & 63]
+		j += 4
+	}
+
+	mod_table := [0, 2, 1]
+	for i = 0; i < mod_table[input_length % 3]; i++ {
+		str[output_length - 1 - i] = `=`
+	}
+
+	return tos(str, output_length)
+}