pcm/Traits: add typedef "sum_type"

src/pcm/PcmChannels.cxx

@@ -44,8 +44,8 @@ static typename Traits::value_type
 StereoToMono(typename Traits::value_type _a,
 	     typename Traits::value_type _b)
 {
-	typename Traits::long_type a(_a);
-	typename Traits::long_type b(_b);
+	typename Traits::sum_type a(_a);
+	typename Traits::sum_type b(_b);
 
 	return typename Traits::value_type((a + b) / 2);
 }
@@ -76,7 +76,7 @@ NToStereo(typename Traits::pointer_type dest,
 	assert((end - src) % src_channels == 0);
 
 	while (src != end) {
-		typename Traits::long_type sum = *src++;
+		typename Traits::sum_type sum = *src++;
 		for (unsigned c = 1; c < src_channels; ++c)
 			sum += *src++;
 
@@ -101,7 +101,7 @@ NToM(typename Traits::pointer_type dest,
 	assert((end - src) % src_channels == 0);
 
 	while (src != end) {
-		typename Traits::long_type sum = *src++;
+		typename Traits::sum_type sum = *src++;
 		for (unsigned c = 1; c < src_channels; ++c)
 			sum += *src++;
 

src/pcm/PcmMix.cxx

@@ -125,7 +125,7 @@ template<SampleFormat F, class Traits=SampleTraits<F>>
 static typename Traits::value_type
 PcmAdd(typename Traits::value_type _a, typename Traits::value_type _b)
 {
-	typename Traits::long_type a(_a), b(_b);
+	typename Traits::sum_type a(_a), b(_b);
 
 	return PcmClamp<F, Traits>(a + b);
 }

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 adding
+	 * two values without risking an (integer) overflow or
+	 * (floating point) precision loss.
+	 */
+	typedef int sum_type;
+
+	/**
 	 * A "long" type that is large and accurate enough for
 	 * arithmetic without risking an (integer) overflow or
 	 * (floating point) precision loss.
@@ -75,6 +82,7 @@ struct SampleTraits<SampleFormat::S16> {
 	typedef value_type *pointer_type;
 	typedef const value_type *const_pointer_type;
 
+	typedef int_least32_t sum_type;
 	typedef int_least32_t long_type;
 
 	static constexpr size_t SAMPLE_SIZE = sizeof(value_type);
@@ -87,6 +95,7 @@ struct SampleTraits<SampleFormat::S32> {
 	typedef value_type *pointer_type;
 	typedef const value_type *const_pointer_type;
 
+	typedef int_least64_t sum_type;
 	typedef int_least64_t long_type;
 
 	static constexpr size_t SAMPLE_SIZE = sizeof(value_type);
@@ -99,6 +108,7 @@ struct SampleTraits<SampleFormat::S24_P32> {
 	typedef value_type *pointer_type;
 	typedef const value_type *const_pointer_type;
 
+	typedef int_least32_t sum_type;
 	typedef int_least64_t long_type;
 
 	static constexpr size_t SAMPLE_SIZE = sizeof(value_type);
@@ -111,6 +121,7 @@ struct SampleTraits<SampleFormat::FLOAT> {
 	typedef value_type *pointer_type;
 	typedef const value_type *const_pointer_type;
 
+	typedef float sum_type;
 	typedef float long_type;
 
 	static constexpr size_t SAMPLE_SIZE = sizeof(value_type);