Partial Revert "audio: simplified samples storing/loading"

The loading of samples with negative value was not working properly
because of sign expansion. The storing works fine, because samples are
only ever written with the same or less BPS.

This reverts commit 586c3fc.

src/audio/utils.cpp

@@ -76,23 +76,34 @@ static void format_to_out_bps(char *out, int bps, int32_t out_value);
  * Loads sample with BPS width and returns it cast to
  * int32_t.
  */
-template <int BPS>
-static int32_t
-load_sample(const char *data)
-{
-        int32_t ret = 0;
-#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
-        memcpy(&ret, data, BPS);
-#else
-        memcpy((char *) &ret + 4 - BPS, data, BPS);
-#endif
-        return ret;
+template<int BPS> static int32_t load_sample(const char *data);
+
+template<> int32_t load_sample<1>(const char *data) {
+        return *reinterpret_cast<const int8_t *>(data);
+}
+
+template<> int32_t load_sample<2>(const char *data) {
+        return *reinterpret_cast<const int16_t *>(data);
+}
+
+template<> int32_t load_sample<3>(const char *data) {
+        int32_t in_value = 0;
+        memcpy(&in_value, data, 3);
+
+        if ((in_value & 1U<<23U) != 0U) { // negative
+                in_value |= 0xFF000000U;
+        }
+
+        return in_value;
+}
+
+template<> int32_t load_sample<4>(const char *data) {
+        return *reinterpret_cast<const int32_t *>(data);
 }
 
 /**
  * @brief Calculates mean and peak RMS from audio samples
  *
- *
  * @param[in]  frame   audio frame
  * @param[in]  channel channel index to calculate RMS to
  * @param[out] peak    peak RMS