From aecd63478e32b17a7896510b50165283c75d6ead Mon Sep 17 00:00:00 2001
From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Date: Mon, 1 Apr 2024 00:03:09 +0200
Subject: [PATCH] avcodec/dsd: Hoist branch out of loop

This is possible by not converting from LSBF to MSBF; instead
add LSBF LUTs.
This approach necessitates reversing the initial values.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavcodec/dsd.c    | 12 ++++++++----
 libavcodec/dsddec.c |  3 ++-
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/libavcodec/dsd.c b/libavcodec/dsd.c
index ec63a706f6..1093c5e2dd 100644
--- a/libavcodec/dsd.c
+++ b/libavcodec/dsd.c
@@ -68,7 +68,8 @@ static const double htaps[HTAPS] = {
      3.423230509967409e-07,  1.244182214744588e-07,  3.130441005359396e-08
 };
 
-static double ctables[CTABLES][256];
+static double ctables_lsbf[CTABLES][256];
+static double ctables_msbf[CTABLES][256];
 
 static av_cold void dsd_ctables_tableinit(void)
 {
@@ -81,8 +82,10 @@ static av_cold void dsd_ctables_tableinit(void)
             for (t = 0; t < CTABLES; ++t)
                 acc[t] += sign * htaps[t * 8 + m];
         }
-        for (t = 0; t < CTABLES; ++t)
-            ctables[CTABLES - 1 - t][e] = acc[t];
+        for (t = 0; t < CTABLES; ++t) {
+            ctables_msbf[CTABLES - 1 - t][e] = acc[t];
+            ctables_lsbf[CTABLES - 1 - t][ff_reverse[e]] = acc[t];
+        }
     }
 }
 
@@ -100,13 +103,14 @@ void ff_dsd2pcm_translate(DSDContext* s, size_t samples, int lsbf,
     unsigned pos, i;
     uint8_t* p;
     double sum;
+    const double (*const ctables)[256] = lsbf ? ctables_lsbf : ctables_msbf;
 
     pos = s->pos;
 
     memcpy(buf, s->buf, sizeof(buf));
 
     while (samples-- > 0) {
-        buf[pos] = lsbf ? ff_reverse[*src] : *src;
+        buf[pos] = *src;
         src += src_stride;
 
         p = buf + ((pos - CTABLES) & FIFOMASK);
diff --git a/libavcodec/dsddec.c b/libavcodec/dsddec.c
index 2bb2e73b75..dd1ea83784 100644
--- a/libavcodec/dsddec.c
+++ b/libavcodec/dsddec.c
@@ -56,7 +56,8 @@ static av_cold int decode_init(AVCodecContext *avctx)
     if (!s)
         return AVERROR(ENOMEM);
 
-    silence = DSD_SILENCE;
+    silence = avctx->codec_id == AV_CODEC_ID_DSD_LSBF_PLANAR ||
+              avctx->codec_id == AV_CODEC_ID_DSD_LSBF ? DSD_SILENCE_REVERSED : DSD_SILENCE;
     for (i = 0; i < avctx->ch_layout.nb_channels; i++) {
         s[i].pos = 0;
         memset(s[i].buf, silence, sizeof(s[i].buf));