[FFmpeg-devel] [PATCHv3 3/3] lavc/vorbisdec: use intermediate variables

[remi at remlab.net]

From: Rémi Denis-Courmont <remi at remlab.net>

The compiler cannot infer that the two float vectors do not alias,
causing unnecessary extra loads and serialisation. This patch caches
the two input values in local variables so that compiler can optimise
individual loop iterations.
---
 libavcodec/vorbisdec.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/libavcodec/vorbisdec.c b/libavcodec/vorbisdec.c
index 10d187b82a..72b8e8e15b 100644
--- a/libavcodec/vorbisdec.c
+++ b/libavcodec/vorbisdec.c
@@ -1581,22 +1581,22 @@ static inline int vorbis_residue_decode(vorbis_context *vc, vorbis_residue *vr,
 
 void ff_vorbis_inverse_coupling(float *mag, float *ang, ptrdiff_t blocksize)
 {
-    for (ptrdiff_t i = 0; i < blocksize; i++) {
-        if (mag[i] > 0.0) {
-            if (ang[i] > 0.0) {
-                ang[i] = mag[i] - ang[i];
+    for (ptrdiff_t i = 0;  i < blocksize;  i++) {
+        float angi = ang[i], magi = mag[i];
+
+        if (magi > 0.f) {
+            if (angi > 0.f) {
+                ang[i] = magi - angi;
             } else {
-                float temp = ang[i];
-                ang[i]     = mag[i];
-                mag[i]    += temp;
+                ang[i] = magi;
+                mag[i] = magi + angi;
             }
         } else {
-            if (ang[i] > 0.0) {
-                ang[i] += mag[i];
+            if (angi > 0.f) {
+                ang[i] = magi + angi;
             } else {
-                float temp = ang[i];
-                ang[i]     = mag[i];
-                mag[i]    -= temp;
+                ang[i] = magi;
+                mag[i] = magi - angi;
             }
         }
     }
-- 
2.37.2