updated comments

src/lib.rs

@@ -8,16 +8,16 @@ pub fn encode(bytes: Vec<u8>) -> String {
         let b1 = chunk.get(1).copied().unwrap_or(0) as u32;
         let b2 = chunk.get(2).copied().unwrap_or(0) as u32;
 
-        // 24-bit number
+        // make 24-bit number from 3 Bytes
         let triple = (b0 << 16) | (b1 << 8) | b2;
 
-        // in 6-bit indices
+        // pull out 6-bit indices
         let i0 = ((triple >> 18) & 0x3F) as usize;
         let i1 = ((triple >> 12) & 0x3F) as usize;
         let i2 = ((triple >> 6) & 0x3F) as usize;
         let i3 = (triple & 0x3F) as usize;
 
-        // at least 1 chunk of 8-bit input
+        // at least 1 chunk of 8-bit input is guaranteed valid
         // so at least 2 chunks of 6-bit window is valid
         output.push(BASE64_ALPHABET[i0] as char);
         output.push(BASE64_ALPHABET[i1] as char);
@@ -57,4 +57,5 @@ mod tests {
         let base64 = encode(bytes);
         assert_eq!(base64, String::from("Zg=="));
     }
+    // todo: add more tests
 }