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.

decoder/dsf: simplify dsf_to_pcm_order()
d8782ce5 · Max Kellermann · dedc2986 · d8782ce5
Commit d8782ce5 authored Aug 22, 2014 by Max Kellermann
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Showing with 5 additions and 10 deletions

DsfDecoderPlugin.cxx src/decoder/plugins/DsfDecoderPlugin.cxx +5 -10

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--- 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,