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

Message ID 20220919161044.19545-3-remi@remlab.net
State Accepted
Commit 5c15cb138eb1292bc16e64d3cb39953f1c09ce97
Headers show
Series [FFmpeg-devel,PATCHv3,1/3] lavc/vorbisdec: use ptrdiff_t to iterate over intptr_t | expand

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Commit Message

Rémi Denis-Courmont Sept. 19, 2022, 4:10 p.m. UTC 
From: Rémi Denis-Courmont <remi@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(-)
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Patch

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;
             }
         }
     }