[FFmpeg-devel] [PATCH 1/2] libswresample: Avoid needlessly large on-stack array.

[Reimar Döffinger]

We only actually need to use a tiny part of it.
Unfortunately we seem to have no real test coverage on
the code, so this is a bit risky.

Signed-off-by: Reimar Döffinger <reimar.doeffin...@gmx.de>
---
 libswresample/rematrix.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/libswresample/rematrix.c b/libswresample/rematrix.c
index bf2abcf..01276b1 100644
--- a/libswresample/rematrix.c
+++ b/libswresample/rematrix.c
@@ -56,6 +56,7 @@
 #define TOP_BACK_LEFT          15
 #define TOP_BACK_CENTER        16
 #define TOP_BACK_RIGHT         17
+#define NUM_NAMED_CHANNELS     18
 
 int swr_set_matrix(struct SwrContext *s, const double *matrix, int stride)
 {
@@ -111,8 +112,8 @@ static int sane_layout(int64_t layout){
 
 av_cold static int auto_matrix(SwrContext *s)
 {
-    int i, j, out_i;
-    double matrix[64][64]={{0}};
+    int i, j, out_i, in_i;
+    double matrix[NUM_NAMED_CHANNELS][NUM_NAMED_CHANNELS]={{0}};
     int64_t unaccounted, in_ch_layout, out_ch_layout;
     double maxcoef=0;
     char buf[128];
@@ -145,7 +146,7 @@ av_cold static int auto_matrix(SwrContext *s)
     }
 
     memset(s->matrix, 0, sizeof(s->matrix));
-    for(i=0; i<64; i++){
+    for(i=0; i<FF_ARRAY_ELEMS(matrix); i++){
         if(in_ch_layout & out_ch_layout & (1ULL<<i))
             matrix[i][i]= 1.0;
     }
@@ -295,10 +296,10 @@ av_cold static int auto_matrix(SwrContext *s)
             av_assert0(0);
     }
 
-    for(out_i=i=0; i<64; i++){
+    for(out_i=i=0; i<FF_ARRAY_ELEMS(matrix); i++){
         double sum=0;
-        int in_i=0;
-        for(j=0; j<64; j++){
+        in_i=0;
+        for(j=0; j<FF_ARRAY_ELEMS(matrix[0]); j++){
             s->matrix[out_i][in_i]= matrix[i][j];
             if(matrix[i][j]){
                 sum += fabs(matrix[i][j]);
@@ -310,6 +311,16 @@ av_cold static int auto_matrix(SwrContext *s)
         if(out_ch_layout & (1ULL<<i))
             out_i++;
     }
+    for (; i < 64; i++) {
+        if (in_ch_layout & out_ch_layout & (1ULL<<i)) {
+            s->matrix[out_i][in_i] = 1.0;
+            maxcoef = FFMAX(maxcoef, 1.0);
+        }
+        if (in_ch_layout & (1ULL<<i))
+            in_i++;
+        if (out_ch_layout & (1ULL<<i))
+            out_i++;
+    }
     if(s->rematrix_volume  < 0)
         maxcoef = -s->rematrix_volume;
 
-- 
2.1.0

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