From 3f6874f4d7f1a6b3903df5986b823faac127fd54 Mon Sep 17 00:00:00 2001
From: Christoph Heinrich <christoph.heinrich@student.tugraz.at>
Date: Fri, 29 Sep 2023 20:30:41 +0200
Subject: [PATCH] af_scaletempo: don't use a window for offset search

This might seem counter intuitive at first, but we want to change the
sound in total as little as possible, not only the middle part of the
overlap.

This also removes the loop unrolling from the integer path to keep it as
close to the float path as possible. The difference in performance is
fairly small and if such an optimization is deemed desirable in the
future it should be implemented for both float and integer
---
 audio/filter/af_scaletempo.c | 73 ++++--------------------------------
 1 file changed, 8 insertions(+), 65 deletions(-)

diff --git a/audio/filter/af_scaletempo.c b/audio/filter/af_scaletempo.c
index c947bbb22e..29b692b9ac 100644
--- a/audio/filter/af_scaletempo.c
+++ b/audio/filter/af_scaletempo.c
@@ -88,8 +88,6 @@ struct priv {
     // best overlap
     int frames_search;
     int num_channels;
-    void *buf_pre_corr;
-    void *table_window;
     int (*best_overlap_offset)(struct priv *s);
 };
 
@@ -136,27 +134,19 @@ static bool fill_queue(struct priv *s)
     return bytes_needed == 0;
 }
 
-#define UNROLL_PADDING (4 * 4)
-
 static int best_overlap_offset_float(struct priv *s)
 {
     float best_corr = INT_MIN;
     int best_off = 0;
 
-    float *pw  = s->table_window;
-    float *po  = s->buf_overlap;
-    po += s->num_channels;
-    float *ppc = s->buf_pre_corr;
-    for (int i = s->num_channels; i < s->samples_overlap; i++)
-        *ppc++ = *pw++ **po++;
-
     float *search_start = (float *)s->buf_queue + s->num_channels;
     for (int off = 0; off < s->frames_search; off++) {
         float corr = 0;
         float *ps = search_start;
-        ppc = s->buf_pre_corr;
+        float *po = s->buf_overlap;
+        po += s->num_channels;
         for (int i = s->num_channels; i < s->samples_overlap; i++)
-            corr += *ppc++ **ps++;
+            corr += *po++ * *ps++;
         if (corr > best_corr) {
             best_corr = corr;
             best_off  = off;
@@ -172,28 +162,14 @@ static int best_overlap_offset_s16(struct priv *s)
     int64_t best_corr = INT64_MIN;
     int best_off = 0;
 
-    int32_t *pw  = s->table_window;
-    int16_t *po  = s->buf_overlap;
-    po += s->num_channels;
-    int32_t *ppc = s->buf_pre_corr;
-    for (long i = s->num_channels; i < s->samples_overlap; i++)
-        *ppc++ = (*pw++ **po++) >> 15;
-
     int16_t *search_start = (int16_t *)s->buf_queue + s->num_channels;
     for (int off = 0; off < s->frames_search; off++) {
         int64_t corr = 0;
         int16_t *ps = search_start;
-        ppc = s->buf_pre_corr;
-        ppc += s->samples_overlap - s->num_channels;
-        ps  += s->samples_overlap - s->num_channels;
-        long i  = -(s->samples_overlap - s->num_channels);
-        do {
-            corr += ppc[i + 0] * (int64_t)ps[i + 0];
-            corr += ppc[i + 1] * (int64_t)ps[i + 1];
-            corr += ppc[i + 2] * (int64_t)ps[i + 2];
-            corr += ppc[i + 3] * (int64_t)ps[i + 3];
-            i += 4;
-        } while (i < 0);
+        int16_t *po = s->buf_overlap;
+        po += s->num_channels;
+        for (int i = s->num_channels; i < s->samples_overlap; i++)
+            corr += *po++ * (int32_t)*ps++;
         if (corr > best_corr) {
             best_corr = corr;
             best_off  = off;
@@ -449,39 +425,8 @@ static bool reinit(struct mp_filter *f)
         s->best_overlap_offset = NULL;
     else {
         if (use_int) {
-            int64_t t = frames_overlap;
-            int32_t n = 8589934588LL / (t * t); // 4 * (2^31 - 1) / t^2
-            s->buf_pre_corr = realloc(s->buf_pre_corr,
-                                        s->bytes_overlap * 2 + UNROLL_PADDING);
-            s->table_window = realloc(s->table_window,
-                                        s->bytes_overlap * 2 - nch * bps * 2);
-            if (!s->buf_pre_corr || !s->table_window) {
-                MP_FATAL(f, "Out of memory\n");
-                return false;
-            }
-            memset((char *)s->buf_pre_corr + s->bytes_overlap * 2, 0,
-                    UNROLL_PADDING);
-            int32_t *pw = s->table_window;
-            for (int i = 1; i < frames_overlap; i++) {
-                int32_t v = (i * (t - i) * n) >> 15;
-                for (int j = 0; j < nch; j++)
-                    *pw++ = v;
-            }
             s->best_overlap_offset = best_overlap_offset_s16;
         } else {
-            s->buf_pre_corr = realloc(s->buf_pre_corr, s->bytes_overlap);
-            s->table_window = realloc(s->table_window,
-                                        s->bytes_overlap - nch * bps);
-            if (!s->buf_pre_corr || !s->table_window) {
-                MP_FATAL(f, "Out of memory\n");
-                return false;
-            }
-            float *pw = s->table_window;
-            for (int i = 1; i < frames_overlap; i++) {
-                float v = i * (frames_overlap - i);
-                for (int j = 0; j < nch; j++)
-                    *pw++ = v;
-            }
             s->best_overlap_offset = best_overlap_offset_float;
         }
     }
@@ -491,7 +436,7 @@ static bool reinit(struct mp_filter *f)
 
     s->bytes_queue = (s->frames_search + s->frames_stride + frames_overlap)
                         * bps * nch;
-    s->buf_queue = realloc(s->buf_queue, s->bytes_queue + UNROLL_PADDING);
+    s->buf_queue = realloc(s->buf_queue, s->bytes_queue);
     if (!s->buf_queue) {
         MP_FATAL(f, "Out of memory\n");
         return false;
@@ -553,9 +498,7 @@ static void af_scaletempo_destroy(struct mp_filter *f)
     struct priv *s = f->priv;
     free(s->buf_queue);
     free(s->buf_overlap);
-    free(s->buf_pre_corr);
     free(s->table_blend);
-    free(s->table_window);
     TA_FREEP(&s->in);
     mp_filter_free_children(f);
 }