From 2358fabb709bcadd300c46e11e74d48f2b115d8e Mon Sep 17 00:00:00 2001
From: Andree Buschmann <AndreeBuschmann@t-online.de>
Date: Tue, 19 Apr 2011 05:55:54 +0000
Subject: Optimization to latest aac decoder changes. Significantly reduce loop
 count in m4a_check_sample_offset() during standard playback. Before this
 change the loop count increased with each decoded chunk and for each frame.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@29750 a1c6a512-1295-4272-9138-f99709370657
---
 apps/codecs/aac.c        |  8 +++++---
 apps/codecs/libm4a/m4a.c | 11 ++++++++---
 apps/codecs/libm4a/m4a.h |  2 +-
 3 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/apps/codecs/aac.c b/apps/codecs/aac.c
index 6bb5ac50ae..8eb2dfd8ce 100644
--- a/apps/codecs/aac.c
+++ b/apps/codecs/aac.c
@@ -61,6 +61,7 @@ enum codec_status codec_main(void)
     NeAACDecFrameInfo frame_info;
     NeAACDecHandle decoder;
     int err;
+    uint32_t seek_idx = 0;
     uint32_t s = 0;
     uint32_t sbr_fac = 1;
     unsigned char c = 0;
@@ -201,7 +202,8 @@ next_track:
                 sound_samples_done *= sbr_fac;
                 elapsed_time = (sound_samples_done * 10) / (ci->id3->frequency / 100);
                 ci->set_elapsed(elapsed_time);
-            
+                seek_idx = 0;
+
                 if (i == 0) 
                 {
                     lead_trim = ci->id3->lead_trim;
@@ -215,8 +217,8 @@ next_track:
          * "proper" file can have chunks out of order. Why one would want
          * that an good question (but files with gaps do exist, so who 
          * knows?), so we don't support that - for now, at least.
-         */    
-        file_offset = m4a_check_sample_offset(&demux_res, i);
+         */
+        file_offset = m4a_check_sample_offset(&demux_res, i, &seek_idx);
 
         if (file_offset > ci->curpos)
         {
diff --git a/apps/codecs/libm4a/m4a.c b/apps/codecs/libm4a/m4a.c
index 836cdafda3..84144ea76c 100644
--- a/apps/codecs/libm4a/m4a.c
+++ b/apps/codecs/libm4a/m4a.c
@@ -124,10 +124,14 @@ void stream_create(stream_t *stream,struct codec_api* ci)
 
 /* Check if there is a dedicated byte position contained for the given frame.
  * Return this byte position in case of success or return -1. This allows to
- * skip empty samples. */
-int m4a_check_sample_offset(demux_res_t *demux_res, uint32_t frame)
+ * skip empty samples. 
+ * During standard playback the search result (index i) will always increase. 
+ * Therefor we save this index and let the caller set this value again as start
+ * index when calling m4a_check_sample_offset() for the next frame. This 
+ * reduces the overall loop count significantly. */
+int m4a_check_sample_offset(demux_res_t *demux_res, uint32_t frame, uint32_t *start)
 {
-    uint32_t i = 0;
+    uint32_t i = *start;
     for (i=0; i<demux_res->num_lookup_table; ++i)
     {
         if (demux_res->lookup_table[i].sample > frame ||
@@ -136,6 +140,7 @@ int m4a_check_sample_offset(demux_res_t *demux_res, uint32_t frame)
         if (demux_res->lookup_table[i].sample == frame)
             break;
     }
+    *start = i;
     return demux_res->lookup_table[i].offset;
 }
 
diff --git a/apps/codecs/libm4a/m4a.h b/apps/codecs/libm4a/m4a.h
index e49d14b832..da5401dba4 100644
--- a/apps/codecs/libm4a/m4a.h
+++ b/apps/codecs/libm4a/m4a.h
@@ -137,6 +137,6 @@ unsigned int m4a_seek (demux_res_t* demux_res, stream_t* stream,
     int* current_sample);
 unsigned int m4a_seek_raw (demux_res_t* demux_res, stream_t* stream,
     uint32_t file_loc, uint32_t* sound_samples_done, int* current_sample);
-int m4a_check_sample_offset(demux_res_t *demux_res, uint32_t frame);
+int m4a_check_sample_offset(demux_res_t *demux_res, uint32_t frame, uint32_t *start);
 
 #endif /* STREAM_H */
-- 
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