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[FFmpeg-devel,PATCHv2,2/2] lavc/vorbisdec: use intermediate variables

Message ID 20220919153551.11377-2-remi@remlab.net
State New
Headers show
Series [FFmpeg-devel,PATCHv2,1/2] lavc/vorbisdec: use ptrdiff_t to iterate over intptr_t | expand

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Commit Message

Rémi Denis-Courmont Sept. 19, 2022, 3:35 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 bfc4be6fc6..e59d6e40f0 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, intptr_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;
             }
         }
     }