decoder/dsf: simplify dsf_to_pcm_order()

Don't pass the buffer size to the function, as it's known at compile
time.  Use "restrict" on the pointer arguments, and merge the two
loops, which allows the compiler to optimize this loop with a few SSE2
instructions.

1 files changed, 5 insertions, 10 deletions

diff --git a/src/decoder/plugins/DsfDecoderPlugin.cxx b/src/decoder/plugins/DsfDecoderPlugin.cxx
index 98538a842..8c6c3a03d 100644
--- a/src/decoder/plugins/DsfDecoderPlugin.cxx
+++ b/src/decoder/plugins/DsfDecoderPlugin.cxx
@@ -195,16 +195,11 @@ bit_reverse_buffer(uint8_t *p, uint8_t *end)
  * order.
  */
 static void
-dsf_to_pcm_order(uint8_t *dest, const uint8_t *src, size_t nrbytes)
+dsf_to_pcm_order(uint8_t *gcc_restrict dest, const uint8_t *gcc_restrict src)
 {
-	for (size_t i = 0, j = 0; i < nrbytes; i += 2) {
-		dest[i] = src[j];
-		j++;
-	}
-
-	for (size_t i = 1, j = 0; i < nrbytes; i += 2) {
-		dest[i] = src[DSF_BLOCK_SIZE + j];
-		j++;
+	for (size_t i = 0; i < DSF_BLOCK_SIZE; ++i) {
+		dest[2 * i] = src[i];
+		dest[2 * i + 1] = src[DSF_BLOCK_SIZE + i];
 	}
 }
 
@@ -236,7 +231,7 @@ dsf_decode_chunk(Decoder &decoder, InputStream &is,
 			bit_reverse_buffer(buffer, buffer + block_size);
 
 		uint8_t interleaved_buffer[DSF_BLOCK_SIZE * 2];
-		dsf_to_pcm_order(interleaved_buffer, buffer, block_size);
+		dsf_to_pcm_order(interleaved_buffer, buffer);
 
 		const auto cmd = decoder_data(decoder, is,
 					      interleaved_buffer, block_size,