Cleanup and add tests for convert_channels

src/conversions.rs

@@ -39,9 +39,21 @@ pub fn convert_samples_rate<T>(input: &[T], from: ::SamplesRate, to: ::SamplesRa
     unimplemented!()
 }
 
+/// Converts between a certain number of channels.
+///
+/// If the target number is inferior to the source number, additional channels are removed.
+///
+/// If the target number is superior to the source number, the value of channel `N` is equal
+/// to the value of channel `N % source_channels`.
+///
+/// ## Panic
+///
+/// Panics if `from` is 0, `to` is 0, or if the data length is not a multiple of `from`.
 pub fn convert_channels<T>(input: &[T], from: ::ChannelsCount, to: ::ChannelsCount) -> Vec<T>
                            where T: Copy
 {
+    assert!(from != 0);
+    assert!(to != 0);
     assert!(input.len() % from as uint == 0);
 
     let mut result = Vec::new();
@@ -53,18 +65,41 @@ pub fn convert_channels<T>(input: &[T], from: ::ChannelsCount, to: ::ChannelsCou
         }
 
         // adding extra ones
-        for i in range(0, ::std::cmp::max(0, to - from)) {
+        if to > from {
+            for i in range(0, to - from) {
                 result.push(element[i as uint % element.len()]);
             }
         }
+    }
 
     result
 }
 
-/*#[cfg(test)]
+#[cfg(test)]
 mod test {
-    #[test]
-    fn test_convert_channels() {
+    use super::convert_channels;
 
+    #[test]
+    fn remove_channels() {
+        let result = convert_channels(&[1u16, 2, 3, 1, 2, 3], 3, 2);
+        assert_eq!(result.as_slice(), [1, 2, 1, 2]);
+
+        let result = convert_channels(&[1u16, 2, 3, 4, 1, 2, 3, 4], 4, 1);
+        assert_eq!(result.as_slice(), [1, 1]);
     }
-}*/
+
+    #[test]
+    fn add_channels() {
+        let result = convert_channels(&[1u16, 2, 1, 2], 2, 3);
+        assert_eq!(result.as_slice(), [1, 2, 1, 1, 2, 1]);
+
+        let result = convert_channels(&[1u16, 2, 1, 2], 2, 4);
+        assert_eq!(result.as_slice(), [1, 2, 1, 2, 1, 2, 1, 2]);
+    }
+
+    #[test]
+    #[should_fail]
+    fn convert_channels_wrong_data_len() {
+        convert_channels(&[1u16, 2, 3], 2, 1);
+    }
+}