[FFmpeg-devel] [PATCH v2] avcodec/fft_template: libavcodec/fft_template: improve performance of the ff_fft_init in fft_template

Steven Liu lq at chinaffmpeg.org
Fri Dec 21 12:09:50 EET 2018


Before patch:
init nbits = 17, get 10000 samples, average cost: 16105 us
After patch:
init nbits = 17, get 10000 samples, average cost: 15221 us

Signed-off-by: Steven Liu <lq at chinaffmpeg.org>
---
 libavcodec/fft_template.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/libavcodec/fft_template.c b/libavcodec/fft_template.c
index 762c014bc8..2b528be882 100644
--- a/libavcodec/fft_template.c
+++ b/libavcodec/fft_template.c
@@ -261,17 +261,21 @@ av_cold int ff_fft_init(FFTContext *s, int nbits, int inverse)
     if (s->fft_permutation == FF_FFT_PERM_AVX) {
         fft_perm_avx(s);
     } else {
-        for(i=0; i<n; i++) {
-            int k;
-            j = i;
-            if (s->fft_permutation == FF_FFT_PERM_SWAP_LSBS)
-                j = (j&~3) | ((j>>1)&1) | ((j<<1)&2);
-            k = -split_radix_permutation(i, n, s->inverse) & (n-1);
-            if (s->revtab)
-                s->revtab[k] = j;
-            if (s->revtab32)
-                s->revtab32[k] = j;
-        }
+#define SPLIT_RADIX_PERMUTATION(num) do { \
+    for(i=0; i<n; i++) {\
+        int k;\
+        j = i;\
+        if (s->fft_permutation == FF_FFT_PERM_SWAP_LSBS)\
+        j = (j&~3) | ((j>>1)&1) | ((j<<1)&2);\
+        k = -split_radix_permutation(i, n, s->inverse) & (n-1);\
+        s->revtab##num[k] = j;\
+    }\
+} while(0);
+    if (s->revtab)
+        SPLIT_RADIX_PERMUTATION()
+    if (s->revtab32)
+        SPLIT_RADIX_PERMUTATION(32)
+#undef SPLIT_RADIX_PERMUTATION
     }
 
     return 0;
-- 
2.15.2 (Apple Git-101.1)





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