pcm/Traits: add typedef long_type

src/pcm/Traits.hxx

@@ -51,6 +51,13 @@ struct SampleTraits<SampleFormat::S8> {
 	typedef const value_type *const_pointer_type;
 
 	/**
+	 * A "long" type that is large and accurate enough for
+	 * arithmetic without risking an (integer) overflow or
+	 * (floating point) precision loss.
+	 */
+	typedef int long_type;
+
+	/**
 	 * The size of one sample in bytes.
 	 */
 	static constexpr size_t SAMPLE_SIZE = sizeof(value_type);
@@ -68,6 +75,8 @@ struct SampleTraits<SampleFormat::S16> {
 	typedef value_type *pointer_type;
 	typedef const value_type *const_pointer_type;
 
+	typedef int long_type;
+
 	static constexpr size_t SAMPLE_SIZE = sizeof(value_type);
 	static constexpr unsigned BITS = sizeof(value_type) * 8;
 };
@@ -78,6 +87,8 @@ struct SampleTraits<SampleFormat::S32> {
 	typedef value_type *pointer_type;
 	typedef const value_type *const_pointer_type;
 
+	typedef int64_t long_type;
+
 	static constexpr size_t SAMPLE_SIZE = sizeof(value_type);
 	static constexpr unsigned BITS = sizeof(value_type) * 8;
 };
@@ -88,6 +99,8 @@ struct SampleTraits<SampleFormat::S24_P32> {
 	typedef value_type *pointer_type;
 	typedef const value_type *const_pointer_type;
 
+	typedef int long_type;
+
 	static constexpr size_t SAMPLE_SIZE = sizeof(value_type);
 	static constexpr unsigned BITS = 24;
 };