pcm_channels: added 24 bit implementations

The 24 bit implementation is mostly copy'n'paste of the 16 bit
version, except that the data type is int32_t instead of int16_t.

src/pcm_channels.c

@@ -100,3 +100,82 @@ pcm_convert_channels_16(int8_t dest_channels,
 
 	return buf;
 }
+
+static void
+pcm_convert_channels_24_1_to_2(int32_t *dest, const int32_t *src,
+			       unsigned num_frames)
+{
+	while (num_frames-- > 0) {
+		int32_t value = *src++;
+
+		*dest++ = value;
+		*dest++ = value;
+	}
+}
+
+static void
+pcm_convert_channels_24_2_to_1(int32_t *dest, const int32_t *src,
+			       unsigned num_frames)
+{
+	while (num_frames-- > 0) {
+		int32_t a = *src++, b = *src++;
+
+		*dest++ = (a + b) / 2;
+	}
+}
+
+static void
+pcm_convert_channels_24_n_to_2(int32_t *dest,
+			       unsigned src_channels, const int32_t *src,
+			       unsigned num_frames)
+{
+	unsigned c;
+
+	assert(src_channels > 0);
+
+	while (num_frames-- > 0) {
+		int32_t sum = 0;
+		int32_t value;
+
+		for (c = 0; c < src_channels; ++c)
+			sum += *src++;
+		value = sum / (int)src_channels;
+
+		/* XXX this is actually only mono ... */
+		*dest++ = value;
+		*dest++ = value;
+	}
+}
+
+const int32_t *
+pcm_convert_channels_24(int8_t dest_channels,
+			int8_t src_channels, const int32_t *src,
+			size_t src_size, size_t *dest_size_r)
+{
+	static int32_t *buf;
+	static size_t len;
+	unsigned num_frames = src_size / src_channels / sizeof(*src);
+	unsigned dest_size = num_frames * dest_channels * sizeof(*src);
+
+	if (dest_size > len) {
+		len = dest_size;
+		buf = xrealloc(buf, len);
+	}
+
+	*dest_size_r = dest_size;
+
+	if (src_channels == 1 && dest_channels == 2)
+		pcm_convert_channels_24_1_to_2(buf, src, num_frames);
+	else if (src_channels == 2 && dest_channels == 1)
+		pcm_convert_channels_24_2_to_1(buf, src, num_frames);
+	else if (dest_channels == 2)
+		pcm_convert_channels_24_n_to_2(buf, src_channels, src,
+					       num_frames);
+	else {
+		ERROR("conversion %u->%u channels is not supported\n",
+		      src_channels, dest_channels);
+		return NULL;
+	}
+
+	return buf;
+}

src/pcm_channels.h

@@ -27,4 +27,9 @@ pcm_convert_channels_16(int8_t dest_channels,
 			int8_t src_channels, const int16_t *src,
 			size_t src_size, size_t *dest_size_r);
 
+const int32_t *
+pcm_convert_channels_24(int8_t dest_channels,
+			int8_t src_channels, const int32_t *src,
+			size_t src_size, size_t *dest_size_r);
+
 #endif