lzx-decompress.c: Simplify handling of recent offsets

The recent offsets can all be handled by the same code.  This should
remove at least one branch from the generated code.

diff --git a/src/lzx-decompress.c b/src/lzx-decompress.c
index e1c0160cdfef246ab8e2eba26c2054dc5ea490d0..7389c7c419f9cf23f9b4c56770d84785078f0693 100644 (file)
--- a/src/lzx-decompress.c
+++ b/src/lzx-decompress.c
@@ -552,22 +552,15 @@ lzx_decode_match(unsigned main_element, int block_type,
        /* If the position_slot is 0, 1, or 2, the match offset is retrieved
         * from the LRU queue.  Otherwise, the match offset is not in the LRU
         * queue. */
        /* If the position_slot is 0, 1, or 2, the match offset is retrieved
         * from the LRU queue.  Otherwise, the match offset is not in the LRU
         * queue. */

-       switch (position_slot) {
-       case 0:
-               match_offset = queue->R[0];
-               break;
-       case 1:
-               match_offset = queue->R[1];
-               swap(queue->R[0], queue->R[1]);
-               break;
-       case 2:
-               /* The queue doesn't work quite the same as a real LRU queue,
-                * since using the R2 offset doesn't bump the R1 offset down to
-                * R2. */
-               match_offset = queue->R[2];
-               swap(queue->R[0], queue->R[2]);
-               break;
-       default:
+       if (position_slot <= 2) {
+               /* Note: This isn't a real LRU queue, since using the R2 offset
+                * doesn't bump the R1 offset down to R2.  This quirk allows all
+                * 3 recent offsets to be handled by the same code.  (For R0,
+                * the swap is a no-op.)  */
+               match_offset = queue->R[position_slot];
+               queue->R[position_slot] = queue->R[0];
+               queue->R[0] = match_offset;
+       } else {

                /* Otherwise, the offset was not encoded as one the offsets in
                 * the queue.  Depending on the position slot, there is a
                 * certain number of extra bits that need to be read to fully
                /* Otherwise, the offset was not encoded as one the offsets in
                 * the queue.  Depending on the position slot, there is a
                 * certain number of extra bits that need to be read to fully


@@ -612,7 +605,6 @@ lzx_decode_match(unsigned main_element, int block_type,
                queue->R[2] = queue->R[1];
                queue->R[1] = queue->R[0];
                queue->R[0] = match_offset;
                queue->R[2] = queue->R[1];
                queue->R[1] = queue->R[0];
                queue->R[0] = match_offset;

-               break;

        }
 
        /* Verify that the match is in the bounds of the part of the window
        }
 
        /* Verify that the match is in the bounds of the part of the window