[FFmpeg-devel] [PATCH v2 02/13] avfilter/f_ebur128: simplify sample cache array

[Niklas Haas <ffmpeg@haasn.xyz>]

From: Niklas Haas <git@haasn.dev>

We don't need an X sample cache anymore, and we also can simplify the
access macro slightly.
---
 libavfilter/f_ebur128.c | 29 +++++++++++------------------
 1 file changed, 11 insertions(+), 18 deletions(-)

diff --git a/libavfilter/f_ebur128.c b/libavfilter/f_ebur128.c
index 173a4f75ca..d0707e9ef9 100644
--- a/libavfilter/f_ebur128.c
+++ b/libavfilter/f_ebur128.c
@@ -115,7 +115,6 @@ typedef struct EBUR128Context {
 
     /* Filter caches.
      * The mult by 3 in the following is for X[i], X[i-1] and X[i-2] */
-    double *x;                      ///< 3 input samples cache for each channel
     double *y;                      ///< 3 pre-filter samples cache for each channel
     double *z;                      ///< 3 RLB-filter samples cache for each channel
     double pre_b[3];                ///< pre-filter numerator coefficients
@@ -446,11 +445,10 @@ static int config_audio_output(AVFilterLink *outlink)
                    AV_CH_SURROUND_DIRECT_LEFT               |AV_CH_SURROUND_DIRECT_RIGHT)
 
     ebur128->nb_channels  = nb_channels;
-    ebur128->x            = av_calloc(nb_channels, 3 * sizeof(*ebur128->x));
     ebur128->y            = av_calloc(nb_channels, 3 * sizeof(*ebur128->y));
     ebur128->z            = av_calloc(nb_channels, 3 * sizeof(*ebur128->z));
     ebur128->ch_weighting = av_calloc(nb_channels, sizeof(*ebur128->ch_weighting));
-    if (!ebur128->ch_weighting || !ebur128->x || !ebur128->y || !ebur128->z)
+    if (!ebur128->ch_weighting ||  !ebur128->y || !ebur128->z)
         return AVERROR(ENOMEM);
 
 #define I400_BINS(x)  ((x) * 4 / 10)
@@ -673,34 +671,30 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *insamples)
         MOVE_TO_NEXT_CACHED_ENTRY(3000);
 
         for (ch = 0; ch < nb_channels; ch++) {
-            double bin;
-
             if (ebur128->peak_mode & PEAK_MODE_SAMPLES_PEAKS)
                 ebur128->sample_peaks[ch] = FFMAX(ebur128->sample_peaks[ch], fabs(samples[idx_insample * nb_channels + ch]));
 
-            ebur128->x[ch * 3] = samples[idx_insample * nb_channels + ch]; // set X[i]
-
             if (!ebur128->ch_weighting[ch])
                 continue;
 
             /* Y[i] = X[i]*b0 + X[i-1]*b1 + X[i-2]*b2 - Y[i-1]*a1 - Y[i-2]*a2 */
-#define FILTER(Y, X, NUM, DEN) do {                                             \
-            double *dst = ebur128->Y + ch*3;                                    \
-            double src = ebur128->X[ch*3]  ;                                    \
-            double dst0 = NUM[0] * src + dst[1];                                \
-            dst[1] = NUM[1] * src + dst[2] - DEN[1] * dst0;                     \
-            dst[2] = NUM[2] * src - DEN[2] * dst0;                              \
-            dst[0] = dst0;                                                      \
+#define FILTER(DST, SRC, NUM, DEN) do {                                         \
+            const double tmp = DST[0] = NUM[0] * SRC + DST[1];                  \
+            DST[1] = NUM[1] * SRC + DST[2] - DEN[1] * tmp;                      \
+            DST[2] = NUM[2] * SRC - DEN[2] * tmp;                               \
 } while (0)
 
+            const double x = samples[idx_insample * nb_channels + ch];
+            double *restrict y = &ebur128->y[3 * ch];
+            double *restrict z = &ebur128->z[3 * ch];
+
             // TODO: merge both filters in one?
             FILTER(y, x, ebur128->pre_b, ebur128->pre_a);  // apply pre-filter
-            FILTER(z, y, ebur128->rlb_b, ebur128->rlb_a);  // apply RLB-filter
-
-            bin = ebur128->z[ch * 3] * ebur128->z[ch * 3];
+            FILTER(z, *y, ebur128->rlb_b, ebur128->rlb_a);  // apply RLB-filter
 
             /* add the new value, and limit the sum to the cache size (400ms or 3s)
              * by removing the oldest one */
+            double bin = *z * *z;
             ebur128->i400.sum [ch] = ebur128->i400.sum [ch] + bin - ebur128->i400.cache [ch][bin_id_400];
             ebur128->i3000.sum[ch] = ebur128->i3000.sum[ch] + bin - ebur128->i3000.cache[ch][bin_id_3000];
 
@@ -1073,7 +1067,6 @@ static av_cold void uninit(AVFilterContext *ctx)
     }
 
     av_freep(&ebur128->y_line_ref);
-    av_freep(&ebur128->x);
     av_freep(&ebur128->y);
     av_freep(&ebur128->z);
     av_freep(&ebur128->ch_weighting);
-- 
2.49.0

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